• Volume 129, All articles

      Continuous Article Publishing mode

    • Observational study of a severe snowfall avalanche over a state in North India in November 2019 using GIS

      SUHAIL MEER MOHAMMAD ANOOP KUMAR MISHRA

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      Heavy snowfall in the first week of November 2019 caused snow avalanche that resulted in huge loss in the form of lives and properties over Kashmir Valley in North India. About 17 people were killed including 11 soldiers by the snow avalanche resulting from heavy snowfall. Data from seven stations of India Meteorological Department (IMD) have been used to study the snowfall events. These stations include Kupwara, Gulmarg, Sher-e-Kashmir University of Agricultural Sciences & Technology (SKUAST), Pahalgam, Kokernag, Qazigund and Konibal. Kokernag recorded the highest snowfall of about 120 mm on November 8. SKUAST recorded snowfall of about 80 mm on November 8. Heavy snowfall started on November 6 and lasted up to November 8, 2019. Gulmarg, Kokernag and Kupwara reported cumulative snowfall of more than 100 mm during November 6–8, 2019. These stations are located in hilly region. Heavy snowfall combined with steep slope resulted in heavy snow avalanche causing heavy damage. An army camp situated in northern Gulmarg was swept away due to avalanche resulting in four causalities. Heavy snowfall also affected agriculture, horticulture, transportations and economy of the valley.

      $\bf{Highlights}$

      $\bullet$ A snowfall avalanche event has been explored using GIS over Kashmir Valley.

      $\bullet$ Heavy snowfall combined with steep slope resulted in heavy snow avalanche causing extreme damage.

      $\bullet$ This extreme event affected transportation, agriculture and horticulture.

    • Estimation of Coda Q for northeast India using nonlinear regression

      PARDEEP SANGWAN DINESH KUMAR

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      Classical logarithmic linearization of the single backscattering model to estimate the coda Q ($Q_{c}$) leads to biased results in the presence of low signal-to-noise ratio. Non-linear regression using the Levenberg–Marquardt (L–M) method has been proposed to estimate the $Q_{c}$ in the frequency range of 3–24 Hz on local earthquakes recorded in northeast region of India. Results of both classical log-linear and non-linear approaches to the single backscattering model are compared. On datasets with good signal-to-noise ratio both the approaches lead to almost the same results. However, for datasets having low signal-to-noise ratio, we found that the log-linear technique estimates are biased. Results demonstrate that the log-linear approach overestimates the $Q_{c}$ in comparison to the non-linear approach. Frequency dependence parameter ‘${\eta}$’ for the L–M method is slightly higher than the conventional log-linear approach. The $Q_{c}$ variation with lapse-time is also studied with both the approaches. The biased results of log-linear approach were observed at different frequencies at all lapse times. Significantly lower $Q_{0}$ (1 Hz) estimates of non-linear approach indicated more heterogeneous lithosphere than the log-linear approach.

      $\bf{Highlights}$

      $\bullet$ A novel approach to the single scattering model is proposed wherein nonlinear regression is performed to estimate coda $Q_{c}$.

      $\bullet$ Coda attenuation and its variation with lapse time is analysed (3–24 Hz) from local earthquakes of North East India

      $\bullet$ For datasets having a low signal-to-noise ratio the estimates of the conventional log-linear regression were biased.

      $\bullet$ Significantly lower $Q_{0}$ estimates of the non-linear approach indicated a more heterogeneous lithosphere than a log-linear approach.

    • Analysis of spatio-temporal trend in groundwater elevation data from arsenic affected alluvial aquifers – Case study from Murshidabad district, West Bengal, Eastern India

      RHITWIK CHATTERJEE SWETADRI SAMADDER DEBABRATA MONDAL KALYAN ADHIKARI

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      Fluctuation in groundwater level is a time-dependent stochastic process. It is also a function of various inflow and outflow components to and from the hydrologic system concerned. Depth to water level data are measured through a network of observation wells or hydrograph stations to ascertain the degree of fluctuation in groundwater level at the desired scale, on a long-term basis. Basically, these depths to water level data are point measurements, which can be regarded as random variables furnishing changes in groundwater storage over time. The intrinsic in-homogeneity in aquifer materials introduces variations like jumps, trends, and periodicities in such hydrologic time series data. Thus, trending results from certain gradual, natural and/or anthropogenic interventions in the hydrologic environment and analyses of their trends are imperative for assessment of groundwater level scenario in the area of interest. This in turn, is essential for strategic planning and management for exploitation of the precious groundwater resource in the same area. The area of interest in this article, i.e., Murshidabad is one of the nine arsenic affected districts of West Bengal. Here, contamination persist within, shallow, arseniferous, alluvial aquifers, which are otherwise widely exploited for irrigation purposes. According to many researchers working in this area, over-exploitation of groundwater is the root cause for the plummeting water level and the widespread arsenic contamination as well. The present study intends to detect and analyze the trends persisting in the depth to water level data measured over a period from 1996 to 2016, in Murshidabad district of West Bengal, India, amidst its complex and contrasting hydrogeologic set-up and interpret the results in terms of the hydrologic attributes of the Bengal basin as a whole. The non-parametric Mann–Kendall test and the Sen’s slope estimator have been used to identify the linear trend persisting in the time series pre- and post-monsoon groundwater elevation values. The analysis indicates statistically significant decline in water level across the study area especially during the post-monsoon season. This can be attributed to the recharge–discharge disparity within the hydrologic regime; brought through intense pumping over the study area. Its ill effect being particularly observed in the western part of river Bhagirathi. Findings of such study are crucial for assessment of dynamic groundwater resources of the district and subsequently can be utilized as a decision support tool for groundwater management at micro-level.

      $\bf{Highlights}$

      $\bullet$ Declining trend in ground water level elevation is indicative of startling water crisis over a region; however, assessment of such trend should be performed over a quantitative basis, as; fluctuation in groundwater level is a time-dependent stochastic process.

      $\bullet$ A well-knit methodology (including RL correction, spatial interpolation of data, analyses and quantification of trend present in the data) needs to be followed by the groundwater managers operating at the micro-level to keep an account of aquifer storage conditions.

      $\bullet$ Statistically significant declining trend in water level elevation is observed in the Arsenic affected shallow alluvial aquifers, on either sides of river Bhagirathi.

      $\bullet$ Lack of groundwater replenishment within recoverable recharge, coupled with over extraction causes such drop in groundwater elevation.

      $\bullet$ To combat similar situation groundwater extraction should be restricted within the limit of sustainability and should not exceed natural recharge potential.

    • Study of small-scale structures and their significance in unravelling the accretionary character of Singhbhum shear zone, Jharkhand, India

      ABHINABA ROY ABDUL MATIN

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      Localized strain within tabular ductile shear zones is developed from micro- to meso- to even large scales to form complex structures. They grow in width and length through linkage of segments with progressive accumulation of strain and displacement, and finally produce shear zone networks characterized by anastomosing patterns. Singhbhum shear zone (SSZ) represents a large composite zone characterized by a collage of different dismembered lithotectonic segments, with heterogeneous structural features, within a matrix typical of a shear zone. Structural features indicate that the material properties of protoliths have a great role in controlling the mechanics of deformation. Meso- and micro-scale structural studies of the east-central part of the SSZ reveal ‘tectonic complex like’ (? deeper level equivalent of mélange type complex) assemblage of dismembered lithoteconic units. Shear-induced foliations, S, C and C$^{\prime}$, were developed while the main mylonitic foliation is represented by C-plane. Apart from that, shear lenses are exceptionally well developed in both meso- and micro-scale in most of the units, particularly in schistose rocks. They were formed from different processes during progressive simple shear, which includes (1) anastomosing C-planes, (2) intersection between C- and C$^{\prime}$-planes, (3) disruption of stretched out longer limbs of asymmetric folds, and (4) cleavage duplex. Fabrics recorded in rocks indicate that there was a progressive change in the development of predominantly flattening fabric (coaxial pure shear) in the northern part (outside the SSZ), to simple-shear non-coaxial type deformation producing shear fabric, dominating over the flattening fabric, in the southern part (within the SSZ) that is in close proximity with the Singhbhum Craton. Although an overall plane strain simple shear model is apparent, occasional presence of extensional features along two directions of the mylonitic foliation, demonstrative of three-dimensional deformation (simple shear and flattening: X > Y > 1 > Z), may indicate the stretching nature of the SSZ. From the orientation of oblique grain shape fabric [ISA$_{max}$ (${\theta}$ < 45$^{\circ}$)], there is slight deviation from simple shear, i.e., a sub-simple nature of plane strain shear could be inferred. However, in conformity with simple shear model the ubiquitously developed stretching lineation shows consistency in orientation being parallel to the movement direction. There is no evidence of transpression. Shear sense indicators invariably indicate up-dip ductile thrust movement with vergence top-to-the south. Microstructural deformational characteristics indicate that peak temperature attained during the deformation in shear zone was ${\sim}$600$^{\circ}$C. Prolonged period of metasomatism, induced by fluid influx, played an important role in strain softening during the development of SSZ.

      $\bf{Highlights}$

      $\bullet$ Meso- to micro-scale structures in Singhbhum Shear Zone (SSZ) show imprints of shear induced foliations, S, C and C$^{\prime}$ and formation of shear lenses attesting protracted progressive deformation.

      $\bullet$ SSZ characterizes accretionary character with dismembered heterogeneous lithotectonic units similar to tectonic complex zone.

      $\bullet$ Shear sense criteria consistently show top-to-south movement of the hanging wall of SSZ.

      $\bullet$ A gradual transition from predominantly flattening deformation in the northern hanging wall to dominantly simple shear with subordinate flattening in the SSZ. Boundary conditions suggest stretching nature of SSZ.

      $\bullet$ Fluid influx played immense role in strain softening during deformation.

    • Fine particulate pollution and ambient air quality: A case study over an urban site in Delhi, India

      JANHAVI SINGH PRIYANSHU GUPTA DEEPAK GUPTA SUNITA VERMA DIVYA PRAKASH SWAGATA PAYRA

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      The current study discourses the impact of variation in PM$_{2.5}$ concentration on the ambient air quality of Delhi. The 24-hourly PM$_{2.5}$ concentration dataset was obtained from air quality measurement site (Anand Vihar) of Delhi Pollution Control Committee (DPCC) for the duration of April 2015 to December 2018. The annual and seasonal variability in the trend of ambient PM$_{2.5}$ along with cumulative impact of meteorological parameters have been analyzed. The overall percentage increase in annual PM$_{2.5}$ concentration, compared to National Ambient Air Quality Standards (NAAQS) guidelines, is observed to be 286.09%. The maximum concentration of fine particulate matter was recorded to be 788.6 $\mu$g/m$^{3}$ during post-monsoon season and it was found to be associated with lower ambient temperature of 21.34${\circ}$C and wind speed of 0.33 m/sec. Further, PM$_{2.5}$ concentration was found to be correlated with CO (R= 0.6515) and NH$_{3}$ (R= 0.6396) indicating similar sources of emission. Further, backward trajectory analysis revealed contribution in PM$_{2.5}$ concentration from the states of Punjab and Haryana. The results indicated that particulate pollution is likely to occur in urban atmospheric environments with low temperatures and low wind speeds.

      $\bf{Highlights}$

      $\bullet$ PM$_{2.5}$/PM$_{10}$ ratio was observed to be highest in November, December and January, attributing aggravated levels of particle pollution to anthropogenic sources.

      $\bullet$ Seasonal analysis of PM$_{2.5}$ concentration indicated that particulate pollution was severe during post monsoon and winter months.

      $\bullet$ Carbon monoxide (R = 0.6515; $R^{2}$ = 0.4244) and Ammonia (R = 0.6396; $R^{2}$ = 0.4088) were found to be correlated with PM$_{2.5}$.

    • Provenance and palaeoenvironmental significance of microtextures in quartz and zircon grains from the Paseo del Mar and Bosque beaches, Gulf of Mexico

      MAYLA A RAMOS-VAZQUEZ JOHN S ARMSTRONG-ALTRIN

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      Microtextures of quartz and zircon grains from the Bosque and Paseo del Mar beaches in the Gulf of Mexico were examined using a Scanning Electron Microscopy (SEM), to infer their provenance and palaeoenvironment. A total of 16 microtextures from 200 grains were identified and were grouped into mechanical, chemical, and mechanical/chemical origin. Microtextures of mechanical origin represent parallel striations (ps), cracks due to collision (ck), conchoidal fractures (cf), v-shaped marks (vs), abrasion fatigue (af), meandering ridges (mr), chattermarks (ch), curved (cg) and straight grooves (sg), which are attributed to a high-energy fluvial and sub-aqueous marine environment. Solution pits (sp), crystal overgrowth (cro), and silica globules (sgl) of chemical origin indicated precipitation and dissolution in a silica saturated marine environment. Adhered particles (ap), elongated depressions (dp), and relief are grouped as mechanical/chemical origin, suggested a sub-aqueous nearshore marine environment. Although zircon is considered as a resistant mineral, the frequency of microtextures observed was higher in zircon than in quartz. The results of this study revealed that the Los Tuxtlas volcanic field, Chiapas Massif and Oaxacan Complexes in the SW Gulf of Mexico are the potential source areas, which supplied sediments to the Paseo del Mar and Bosque beach areas.

      $\bf{Highlights}$

      $\bullet$ Microtextures of quartz and zircon grains in the Bosque and Paseo del Mar beaches in the SW Gulf of Mexico were analyzed.

      $\bullet$ Frequency of microtextures are higher in zircon than in quartz grains revealed that microtextures are independent of grain hardness.

      $\bullet$ The dominance of microtextures of chemical origin in the Paseo del Mar beach suggested a low-energy environment with carbonate rich sediments.

      $\bullet$ Chiapas Massif and Oaxacan Complexes are identified as the potential source areas, which supplied sediments to the beach areas.

    • Tectonics of the Indian subcontinent

      RAM S SHARMA

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    • Uncertainty in hydrological analysis using multi-GCM predictions and multi-parameters under RCP 2.6 and 8.5 scenarios in Manipur River basin, India

      VICKY ANAND BAKIMCHANDRA OINAM BIKASH RANJAN PARIDA

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      Climate change is likely to have adverse impacts on hydrological processes in a river basin, by altered runoff due to modifications in land use/land cover (LULC) and catchment hydrology. Substantial uncertainty exists to evaluate impacts of climate change on river catchment due to uncertainty in general circulation model (GCM) projections. In this study, impact of climate change on water balance and hydrological regime of Manipur River basin was investigated using SWAT model. A comprehensive semi-distributed soil and water assessment tool (SWAT) was used for future projection of changes in hydrological regime of Manipur River basin based on two representative concentration pathways (RCP 2.6 and RCP 8.5). A coupled model intercomparison project’s (CMIP5) based GCM downscaled outputs and future LULC projected data were used in the analysis. The projected temperature is likely to be increased by 2.84$^{\circ}$C and increase of 836 mm in annual average precipitation is projected under RCP 8.5 by 2090s. Change in meteorological condition and LULC will lead to increase in runoff, evapotranspiration and water yield by 57.79 m$^{3}$/s (38.32%), 318.7 mm (54.59%) and 629.72 mm (89.82%), respectively, by the end of 21st century. This study demonstrates the importance of water balance components and its spatial and temporal variation in the Manipur River basin. The key findings of this study reveals that the runoff, evapotranspiration and water yield will increase in the coming decades. Increase in water yield may lead to landslides in the hilly region and flooding in low lying areas in future.

      $\bf{Highlights}$

      $\bullet$ Both precipitation and temperature is likely to increase in Manipur River basin.

      $\bullet$ There is high risk of floods in the lower regions near Loktak Lake and landslides in the northern part of the basin.

      $\bullet$ There is no major concern with regard to water scarcity in the coming decades in Manipur River basin.

      $\bullet$ There is good potential of hydro-power generation in the Manipur River basin because of increase in discharge especially during monsoon and post-monsoon season.

    • New paleomagnetic pole and magnetostratigraphy of the Cauvery Basin sediments, southern India

      VENKATESHWARLU M

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      Magnetostratigraphy or magnetic polarity stratigraphy (MPS) is constructed with paleomagnetic parameters for the Campanian–Maastrichtian (Upper Cretaceous) onshore sediment sequences of the Cauvery Basin, southern India. Twenty-nine sedimentary outcrops in the vicinity of Ariyalur district of Tamil Nadu, India were studied using AF (5–150 mT) and thermal demagnetization (100–700$^{\circ}$C). The observed remanence carrier is attributed to hematite through rock magnetic experiments. The virtual geomagnetic pole (VGP) latitudes were computed using the acquired characteristic remanent magnetization (ChRM) directions. The mean ChRM produce Dm= 338, Im= –38, (${\alpha}_{95}$=23.91$^{\circ}$, k = 15.73, N=60). The mean VGP is estimated at 51.33$^{\circ}$N, 292.71$^{\circ}$E deriving a paleolatitude of 21.3$^{\circ}$S. The constructed magnetic polarity stratigraphy (MPS) is correlated with the standard geomagnetic polarity time scale (GPTS). The composite MPS of these sequences comprises of 12 magnetozones (6 normal and 6 reversed events) that are corroborated with Chron C33n to Chron C30n of the GPTS. The derived paleolatitude position from the present study places Indian subcontinent at little shallow southern latitudes indicating moderately higher drift velocities during Upper Cretaceous.

      $\bf{Highlights}$

      $\bullet$ Magnetic polarity stratigraphy (MPS) is constructed with paleomagnetic parameters for the Campanian–Maastrichtian (Upper Cretaceous) onshore sediment sequences of the Cauvery Basin, southern India.

      $\bullet$ The mean direction results in the declination at 338$^{\circ}$ and inclination at –38$^{\circ}$ ((${\alpha}_{95}$= 23.91) and the pole position at 51$^{\circ}$N, 293$^{\circ}$E with a paleolatitude of 21.3$^{\circ}$S.

      $\bullet$ The MPS of Ariyalur Group sequences of Cauvery Basin recorded 12 magnetozones (6 normal and 6 reversed events) and correlated with GPTS of LaBrecque et al. (1977) from Chron C33n to Chron C30n.

      $\bullet$ The paleolatitude position highlights the higher velocities of the drift of the Indian subcontinent during Upper Cretaceous period.

    • Spatial variability of ground water quality: a case study of Udupi district, Karnataka State, India

      DEEPIKA B V RAMAKRISHNAIAH C R SUJAY RAGHAVENDRA NAGANNA

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      Groundwater is a reliable source of fresh water for domestic and agricultural water users. It supports subsurface ecosystem by balancing the geo-biological and bio-geochemical processes at micro- and macro-scales of the ecosystem. Overexploitation, anthropogenic activities and improper agricultural practices have contributed to the pollution of groundwater sources all around the globe. The water quality index (WQI) is the most extensively used indicator which transforms the water quality information derived from several parameters into a single value/rating to categorize and provide a general perception of water quality standard. Groundwater quality analysis and mapping via geographical information system (GIS) proves to be beneficial in identifying the locations where the groundwater quality is deteriorating. In the current study, the WQI of groundwater was determined for the samples collected from open and tube wells located within the Udupi district of Karnataka state, India. The groundwater quality parameters such as pH, hardness, calcium, chlorides, nitrates, iron, fluoride, sulfates, manganese, sodium, magnesium, potassium, turbidity, and phosphate were analyzed for water samples collected from 112 randomly chosen open/tube wells in order to determine the WQI. Interpolation approaches such as inverse distance weighting (IDW) and kriging were adopted in the GIS environment to quantify the spatial variability of groundwater quality over the entire geographical area. The groundwater quality maps were generated using the best fit models. The results portray that, the accuracy of interpolation using IDW and kriging methods was dependent on the measures of central tendency and variability of water quality data of different parameters. The kriging interpolation was much accurate for most of the groundwater quality parameters compared to IDW maps. The WQI maps, perhaps signposted the poor quality of groundwater quality in about 1.88% of the geographical area of Udupi district. Further, about 21.69% of the area was affected by poor quality of groundwater where suitable strategies for replenishment of groundwater resources should be taken up by the concerned authorities. The spatial distribution maps of groundwater quality aid to locate vulnerable places where immediate action is required.

      $\bf{Highlights}$

      $\bullet$ Water quality index mapping clearly depicts the critical areas that need policy measures for the groundwater sustainability.

      $\bullet$ Current study acts as a decision support system for taking up water quality management activities for groundwater remediation in the study area.

      $\bullet$ Geostatistical methods prove to be ideal for the evaluation of spatial groundwater quality assessment and distribution.

    • Investigation of anomalous propagation conditions in Central and West African stations using high-resolution GPS radiosonde observations

      KAISSASSOU SAMUEL LENOUO A TANESSONG R S KAMSU TAMO VONDOU A POKAM W KANKO J

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      A comprehensive study on the anomalous propagation (AP) conditions occurring over the central and west African stations was made from 2 years (January 2005–December 2006) high-resolution data measured by GPS (Global Positioning System) radio survey observations. Through data quality control and diagnostic analysis, the probability of AP occurrence and characteristic quantities of the three typical anomalous propagation conditions were given. The sub-refraction, super-refraction and ducting cases were investigated statistically using the vertical profile of modified refractivity gradient. Strong diurnal variation in the percentage occurrence of the AP had its peak during the wet months, while the dry months had the lowest values. From 0600 to 1800 local time (LT) at day (1800–0600 LT at night), the total percentage occurrence of super-refraction, sub-refraction and ducting were 82.5% (78.5%), 11% (15.5%) and 6.5% (6%), respectively. Besides statistical results, local meteorological conditions prevailing over central and west Africa have also been discussed.

      $\bf{Highlights}$

      $\bullet$ Seasonal maps of occurrence of sub-refraction, super-refraction and ducting layers have been constructed.

      $\bullet$ The daytime (0006–1800 local time) is seldom affected by ducting as a result of the ceaseless and intense heat activity.

      $\bullet$ The refractivity index was obtained from in-situ measurements performed at the 19 stations.

      $\bullet$ Sub-refractive prevails at daytime whereas super-refractive and ducting are observed at night time (1800–0006 local time).

    • 2D thermal modelling along the seismic section Kuppam–Bommidi in Southern Granulitic terrain of Indian Shield

      HARINI GURUHAPPA SHINDE G N VIJAY KUMAR T RAMANA D V KIRTI SRIVASTAVA

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      The crustal structure along the 90 km seismic profile from Kuppam to Bommidi in the southern part of Archean Dharwar Craton and Southern Granulitic terrain is used to obtain a 2D thermal structure for the region. The temperatures are computed for known values of the radiogenic heat production, thermal conductivity and associated boundary conditions. The heterogeneous nature of the subsurface compels one to consider the controlling parameters to be a realization of a random process, as estimation of realistic values for these parameters is very difficult. Uncertainties in the model in such a situation can be analyzed by solving the governing heat conduction equation with its associated boundary conditions from a stochastic point of view. A 2D thermal model for this area is obtained using the finite element method for the heat conduction problem using the COMSOL Multiphysics software. The crustal temperatures for different layers along the 90 km profile is computed by incorporating randomness in thermal conductivity values. Using seismic velocities, the heat production in the layered earth is computed along the profile. The 2D temperature-depth profile along with upper and lower bounds is plotted and results obtained reveal that the temperature varies from 405$^{\circ}$ to 498$^{\circ}$ C at Moho depth along the profile. The errors are varying from 100$^{\circ}$ to 115$^{\circ}$ C. The Moho depth along the profile is seen to vary from 34 to 45 km. At a few locations, the 1D solution along with error bounds is plotted and the results are seen to match well with that of the 2D thermal result at that location.

      $\bf{Highlights}$

      $\bullet$ The 2D crustal thermal structure along with its errors is computed along the 90 km Kuppam–Bommidi profile is the Southern Granulite Terrane.

      $\bullet$ The crustal thermal structure for this profile is solved using the finite element method for the heat conduction problem with surface temperature as one boundary condition and mantle heat flow values as lower boundary conditions and incorporating thermal parameters such as thermal conductivity and heat production along the profile.

      $\bullet$ Variation in thermal structure for changes in thermal conductivity is calculated by incorporation randomness in thermal conductivity values.

      $\bullet$ The crustal temperature varies from 405$^{\circ}$ C to 498$^{\circ}$ C at Moho depth along the profile. The errors are varying from 100$^{\circ}$ C to 115$^{\circ}$ C. The Moho depth in the region varies from 34 to 45 km.

    • Impact of projected climate change on seawater intrusion on a regional coastal aquifer

      SITHARA S PRAMADA S K SANTOSH G THAMPI

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      Sea level rise (SLR) is one of the prime consequences of global warming as pointed out by the Intergovernmental Panel on Climate Change (IPCC). SLR adversely affects coastal regions; triggers coastal erosion, inundation, and affects the freshwater–seawater interface as well. This paper presents the results of a study in which a coastal aquifer under changing climate was simulated using a three-dimensional groundwater model. The study area covers a part of the coastal aquifer in Ernakulam district in the State of Kerala, India. Support Vector Machine (SVM) was used for projection of future sea levels under the representative concentration pathways (RCPs) 4.5 and 8.5, based on the projections of Phase 5 of the Coupled Model Intercomparison Project (CMIP5). Both thermosteric and halosteric components were taken into account in the projection of sea level. It was observed that sea level changes are significantly influenced by the halosteric effect. Results indicate that SLR in the year 2050 with respect to the levels in 2014 will be about 8.64 cm and 12.96 cm under RCPs 4.5 and 8.5, respectively. The repercussions of this rise in sea level on seawater intrusion into the coastal aquifer were evaluated by performing simulations with SEAWAT. Results of the study indicate that the effect of this SLR on seawater intrusion is negligible.

      $\bf{Highlights}$

      $\bullet$ The impact of projected climate change on seawater intrusion in a densely populated coastal region was assessed using a variable density model

      $\bullet$ Local climatic variables influencing sea level were identified

      $\bullet$ Machine learning approach was employed for statistical downscaling of sea level using climatic variables

      $\bullet$ Both thermosteric and halosteric effects were taken in to account in the projection of sea level rise

    • Indian summer monsoon features in the NCEP analysis and forecast system

      RAJU P V S AKHILESH MISHRA SUNDARI A B T

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      The diagnosis of the summer monsoon features over India are investigated using global analysis and forecast system (GFS) of the National Center for Environmental Prediction (NCEP). In addition, the performance of the NCEP GFS model in capturing the observed rainfall variability of the summer monsoon features over India through diagnostic parameters. We delineate the variability between two normal monsoon seasons with basic meteorological fields and significant parameters of kinetic energy, heat and moisture budgets. The 1200 UTC operational analyses and forecasts (day1 through day5) data for summer monsoon seasons of June, July, August and September (JJAS) of 2010 and 2011 are considered. Although both are normal monsoon seasons with seasonal rainfall (JJAS) departure of about −3.1% and 2.1% respectively, during 2010 and 2011, some differences are observed in the spatial distribution of rainfall. The diagnostic fields reasonably reproduced the variations in analyses and forecast fields of up to 5 days. The model forecasts of day1 delineated that the Indian summer monsoon features are well captured, whereas in day3 and day5, forecast depicts some differences. Overall the NCEP analysis and forecast fields not only produces mean monsoonal flow, but also captures seasonal variability realistically. This is evident from the large-scale balances represented by the analyses and model forecasts.

      $\bf{Highlights}$

      $\bullet$ The NCEP global analyses and forecast System depicts less bias in low level circulation in day1 with respect to analysis field, albeit, this bias is increases with increase of forecast period. Overall, the mean monsoon circulation is captured by the NCEP analyzes and forecast system fairly well.

      $\bullet$ The forecast fields illustrate the warm bias in the low levels with maximum over northwest India and monsoon through region, These warm bias in the forecast fields is due to the higher specific humidity over the monsoon trough region.

      $\bullet$ In the forecast of day1, day3 and day5 show the warm bias in the low levels at 925 hPa with maximum over northwest India and monsoon trough region, whereas cold bias is observed over Gujarat and Western Ghat in day3 and day5 forecast.

      $\bullet$ The significant seasonal variability perceived in two normal summer monsoon rainfall. This variability is captured by analysis and model forecasts realistically in terms of diagnostic fields of kinetic energy, heat and moisture.

    • Size distribution of survivor clasts in pseudotachylyte and cataclasite: Implications for crushing and melting processes in seismic fault zones

      ARINDAM SARKAR DIPANJAN BHATTACHARJEE ANUPAM CHATTOPADHYAY

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      Quartz/feldspar fragment (‘clast’) sizes were measured in thin sections of three types of fault zone rocks, e.g., melting-dominated pseudotachylyte (M-Pt), crushing-dominated pseudotachylyte (C-Pt) and cataclasite (Ct), from two well-studied Precambrian shear/fault zones in the Indian craton (e.g., the Gavilgarh–Tan Shear zone in central India and the Sarwar–Junia Fault zone in western India). Logarithmic plots of clast area vs. cumulative frequency in the pseudotachylytes demonstrate a fractal clast-size distribution (c.s.d.) for the intermediate size range, whereas the finer and coarser clast size fractions clearly deviate from the fractal trend. Under-representation of the finer size clasts in the pseudotachylyte samples may be attributed to their preferential melting and removal from the clast population. The relative paucity of coarse clasts, on the other hand, is possibly due to a sampling bias against coarse clasts. The c.s.d of the cataclastic rock shows a multi-fractal character with two different slopes (i.e., lower D-value for finer clast sizes) and absence of the left-hand (finer size) fall off. This suggests less efficient crushing in the finer clast size fraction. The proportion of clasts, compared to the matrix, is very small in M-Pt, increases in C-Pt and is highest in Ct, suggesting that melting of rock/mineral fragments is a dominant process in forming M-Pt, whereas it is less significant in C-Pt, and is absent in Ct, which corroborates the microscopic observations.

      $\bf{Highlights}$

      $\bullet$ Clast size and cumulative frequency were measured in pseudotachylyte and cataclasite samples from two shear zones.

      $\bullet$ Size-frequency relationship follows a power law in melting- and crushing-dominated pseudotachylytes.

      $\bullet$ The power law does not hold good for the finest and coarsest size ranges in both types of pseudotachylytes.

      $\bullet$ For cataclasite, a multi-fractal power law relationship exists between the size and cumulative frequency of clasts.

    • Use of GRACE time-series data for estimating groundwater storage at small scale

      CH SAMUREMBI CHANU HARIKA MUNAGAPATI VM TIWARI ARVIND KUMAR L ELANGO

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      This study integrates the time series of satellite data, i.e. (terrestrial water storage (TWS) extracted from Gravity Recovery and Climate Experiment (GRACE), soil moisture (SM) from Global Land Data Assimilation System (GLDAS), rainfall from Tropical Rainfall Measuring Mission (TRMM)) with in-situ data, i.e. (groundwater (GW) observatory well data and surface water (SW) as reservoir level from Tamil Nadu Public Work Department (TN PWD)) to estimate the water storage of the study area for the period from 2002 March to 2016 December. The study area encompasses three districts of Tamil Nadu State – Chennai, Kancheepuram and Tiruvallur. It was previously observed that the groundwater level in this study area is decreasing at an alarming rate. Trends and residuals of the times series of all the previously stated components were analyzed. Negative trends were observed in the case of $\Delta$SW, $\Delta$SM, $\Delta$GW, $\Delta$TWS-GRACE, but rainfall shows a slight positive trend. Rainfall, being the input for water storage, a marginal increase in rainfall cannot affect the variability of $\Delta$SM, $\Delta$SW, $\Delta$GW and $\Delta$TWS-GRACE. $\Delta$TWS decreases approximately 0.12 cm yr$^{-1}$ averaged water level equal to a total volume −7.5 km$^{3}$. The result of this study shows a decrease in the total storage of groundwater in the study area during the study period from 2002 March to 2016 December. Seawater intrusion due to an increase in sea surface height also shows an impact on $\Delta$TWS derived from grace, in the form of anomalously elevated $\Delta$TWS. A good agreement between $\Delta$TWS-GRACE and $\Delta$TWS- in-situ is found except where sea-water intrusion occurs.

      $\bf{Highlights}$

      $\bullet$ Areal extent of the study area is less than the optimum suggested for GRACE related investigation. The amplitude of the GRACE signal is 300 km and it is recommended that the study area to be larger than that. Our study is perhaps the first such attempt where the study area is much less than recommended.

      $\bullet$ We were able to get a good correlation between $\Delta$GWGRACE and $\Delta$GWINSITU despite the challenge of spatial resolution.

      $\bullet$ A significant finding of the investigation is that distinction in estimates of groundwater changes between GRACE estimates and in-situ perception happens in grids which mostly have sea-area or are intensely impact by urbanization related LULC changes.

      $\bullet$ The impact of various precipitation mechanisms in the examination area was contemplated.

    • A coherent response of Southern Indian Ocean to the Antarctic climate: Implications to the lead, lags of atmospheric CO$_{2}$ during deglaciation

      NARAYANA A C P DIVAKAR NAIDU BHAVANI P G MASOOD AHMAD

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      A record of $\delta^{18}$Oc from the Indian sector of Southern Ocean and atmospheric CO$_{2}$, and $\delta^{18}$O of European Project for Ice Coring in Antarctica (EPICA) and Greenland Ice Sheet Project 2 (GISP2) reveals that a coherent response between $\delta^{18}$O record of Antarctic ice core and the $\delta^{18}$Oc record from Southern Indian Ocean during the deglaciation with initial warming starting around 18 kyr BP which is in agreement with the raise of atmospheric CO$_{2}$ during same time. A distinct asynchrony between the records of $\delta^{18}$Oc from the Southern Indian Ocean and $\delta^{18}$O of GISP2 during the last deglaciation is noticed. We report that Southern Ocean degassing played an important role in raising atmospheric CO$_{2}$ through Atlantic Meridional Overturning Circulation (AMOC), which has an implication in triggering abrupt climate events through coupling of ocean and atmospheric processes.

      $\bf{Highlights}$

      $\bullet$ A synchrony between the temperature variations between the Antarctica and the southern sector of the Indian Ocean are noticed during the deglaciation.

      $\bullet$ Initiation of deglacial warming in the southern sector of Indian Ocean started around 18 Ka which coincides with rise of atmospheric CO$_{2}$ during the same time.

      $\bullet$ Degassing in the Southern Ocean played an important role in raising atmospheric CO$_{2}$ during the deglaciation.

      $\bullet$ Changes in AMOC variations contributed to the trigger of CO$_{2}$ degassing from the deep Southern Ocean.

    • Grain-shape controlled strain in quartz grains in high ductile flow regime: Observations from the Main Central Thrust Zone of the Kumaun Himalaya, India

      A R BHATTACHARYA A K VERMA

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      In ductile shear zones, the strain shown by the rocks depends much on the composition and shape of the mineral constituents. Under simple shear, quartz grains commonly reorient themselves in the direction of tectonic transport or flow. In ductile shear zones, quartz grains are elliptically stretched in the direction of mylonitic foliation to accommodate the imposed ductile strain. Our observations on the rocks of a crustal scale shear zone, the Main Central Thrust (MCT) of the Himalaya, however, reveal that at several places of the shear zone the quartz grains are polygonal and show planar boundaries. The fabric of rocks at such places is not compatible with that of the prevailing fabric of rocks, and can be described as strain insensitive fabric. Following the Panozzo (J. Struct. Geol. 6:215–221, 1984) method, we have estimated strain from quartz grains that show planar boundaries. Our results show that in the MCT zone, the areas of high ductile strain, as existing near the trace of the MCT, the amount of strain shown by such grains of quartz is low, while in areas of low strain, as existing in areas away from the MCT, the amount of strain is relatively higher. As such, the method holds importance in those cases where grain shapes (i.e., planar boundaries) put constraint on estimation of strain because the conventional methods of strain estimation require elliptical shape of objects. This is possibly the first application of the Panozzo method on deformed rocks from India.

      $\bf{Highlights}$

      $\bullet$ The general fabric of rocks of ductile MCT zone of Himalaya is dominated by elliptically deformed quartz grains.

      $\bullet$ However locally the fabric, not compatible with prevailing ductile fabric, contains polygonal quartz grains with flat boundaries.

      $\bullet$ Strain has been estimated for polygonal grains by digitizing their outlines and analysing data by computer software.

      $\bullet$ Such grains show lower strains near MCT and higher strains away. This is reversely shown by elliptically deformed grains.

      $\bullet$ This suggests that the quartz grains with polygonal shapes remained rather insensitive to ductile strain.

    • Bleaching of blue light stimulated luminescence of quartz by moonlight

      RAJAPARA H M VINAYAK KUMAR NAVEEN CHAUHAN GAJJAR P N SINGHV A K

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      Moonlight is sunlight reflected from the moon’s surface. It is additionally modulated by the Earth’s atmosphere, dust and pollutants on its way to the surface of the Earth. This contribution reports the bleaching rates of blue light stimulated luminescence (BLSL) signal of Quartz under full moonlight exposure at the Earth’s surface. Quartz BLSL reduced to 70% by an exposure of 5 hrs moonlight, is in contrast to $\sim$90% reduction in < 3 s with daylight. This was anticipated due to (a) reduced moonlight flux by about a factor of half a million (Agrawal in Lat. Am. J. Phys. Educ. 4(2):325–328, 2010; J. Phys. Astron. 5(1):1–15, 2017); (b) inverse power law dependence of bleaching efficiency on wavelength (Spooner in The validity of optical dating based on feldspar, Ph.D. Thesis, Oxford University, Oxford, 1993; Chen and McKeever in Theory of Thermoluminescence and related phenomena, World Scientific Publications, London, 1997, Chen and Pagonis in Thermally and optically stimulated luminescence: A simulation approach, Wiley and Sons, Chichester, 2011); and (c) moonlight and daylight have spectral peaks around 650 and 550 nm, respectively. Deconvolution of OSL components suggests that moonlight affects the fast component of OSL signal the most. This has ramification for the application in polar regions, where the availability of daylight is at a premium during the winter months. Within a given context, it is conjectured that this could be used to infer the seasonality of sediment transport.

      $\bf{Highlights}$

      $\bullet$ Up to 40% reduction of quartz luminescence signal observed over long moonlight exposure.

      $\bullet$ Moonlight can bleach up to 70% of the fast component of blue light stimulated luminescence signal.

      $\bullet$ Moonlight bleaching may hamper the accuracy of ages of sediments which are only transported during night.

      $\bullet$ Seasonality of sediment deposition can be studied using the bleaching effect of moonlight on quartz.

    • Seasonal variability of tropospheric CO$_{2}$ over India based on model simulation, satellite retrieval and in-situ observation

      KRISHNAPRIYA M RABINDRA K NAYAK ALLAHUDEEN SHAIK BHUVANACHANDRA A DADHWAL V K JHA C S SHESHASAI M V R SASMAL S K PRASAD K V S R

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      In this study, investigation of the seasonal cycle of the tropospheric CO$_{2}$ concentration over India was carried out using the GEOS-Chem atmospheric transport model, Greenhouse gas Observation SATellite (GOSAT) retrievals, and in-situ measurements. The model simulation is highly coherent with the satellite and in-situ datasets, and it shows a distinct seasonal cycle of the tropospheric CO$_{2}$ tendency over India with a negative phase (decreasing concentration) during April–August and a positive phase (increasing concentration) during September–March. The model diagnostics were analyzed to estimate budgets of the surface layer CO$_{2}$, up to 650 hPa pressure level, for the two-phases of the seasonal cycle. A mean tendency, equivalent to −0.70 ppmv month$^{-1}$, observed during April–August, which results from the loss of CO$_{2}$, content in the surface layer through horizontal advection (−2.25 ppmv month$^{-1}$) and vertical diffusion (−0.20 ppmv month$^{-1}$), that dominates the gain from vertical advection (1.53 ppmv month$^{-1}$). The negative contribution of horizontal advection in this period comes from the transport of CO$_{2}$ depleted air-parcels over the oceanic region to India by the southwest monsoon winds and the positive contributions of vertical advection comes from upwelling of CO$_{2}$ enriched air-parcels. The mean tendency, equivalent to 1.01 ppmv month$^{-1}$, during September–March results from the gain through vertical advection (0.78 ppmv month$^{-1}$) and horizontal advection (0.37 ppmv month$^{-1}$) and a small contribution of vertical diffusion (−0.15 ppmv month$^{-1}$). In this period, positive contribution of horizontal advection is due to the transport of CO$_{2}$ enriched air-parcels from the southeast Asian region to India by north-east monsoon winds. At the annual scale, CO$_{2}$ content of the surface layer over India has a net gain of 0.75 GtC that comes from 14.31 GtC through vertical advection that exceeds the loss due to horizontal advection (−11.10 GtC) and vertical diffusion processes (−2.46 GtC). This net gain is almost 85% higher than the input of 0.4 GtC through surface fluxes, which composed of 0.61 GtC anthropogenic emission and −0.21 GtC net terrestrial ecosystem exchanges. Additional sensitivity experiment was carried out to elucidate the semi-annual features of the seasonal cycle of CO$_{2}$ for north India, in contrast to the annual characteristics of the seasonal cycle for south India in relation to the GOSAT observation.

      $\bf{Highlights}$

      $\bullet$ Greenhouse gas Observation SATellite (GOSAT) L3B and L4B retrievals and in-situ flux tower measurements were analysed to describe seasonal cycle of tropospheric CO$_{2}$ over India; and GEOS-Chem atmospheric transport model diagnostics were used to examine the causes of the variability.

      $\bullet$ The seasonal cycle over north India is composed of mixed signature of annual and semi-annual frequencies while south India experiences dominance of annual oscillation. However, the surface layer CO$_{2}$ seasonal tendency has a major negative phase during April–August and a positive phase during September–March.

      $\bullet$ The net negative tendency during April–August results from the loss of CO$_{2}$ from the surface layer through horizontal advection and vertical diffusion processes that dominates the gain from vertical advection; while the net positive tendency during September–March results from the gain through vertical advection and horizontal advection and a small negative contribution from vertical diffusion.

      $\bullet$ At annual scale, the surface layer over India experiences net positive gain of CO$_{2}$ concentration, which is 85% more than the net input from the surface fluxes, and is mostly contributed by large-scale transport processes.

      $\bullet$ Sensitivity experiments were carried out to elucidate the semi-annual features of the seasonal cycle of CO$_{2}$ over north India in relation to the GOSAT observation. It turns out that the secondary trough during October–December on the background of net positive tendency during September–March results from the drawdown of CO$_{2}$ by the terrestrial ecosystem uptake.

    • A new analytical protocol for high precision U–Th–Pb chemical dating of xenotime from the TTG gneisses of the Bundelkhand Craton, central India, using CAMECA SXFive Electron Probe Micro Analyzer

      HIREDYA CHAUHAN APARAJITA TRIPATHI DINESH PANDIT N V CHALAPATHI RAO TALAT AHMAD

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      Xenotime is a significant accessory mineral which is being extensively used for precise U–Th–Pb geochronology by Electron Microprobe Analysis (EPMA). This paper presents a protocol for high analytical precision (<3% uncertainties on the measured ages) developed for the accurate estimation of U–Th and Pb content in xenotime using SXFive EPMA at the Department of Geology, Banaras Hindu University, by deploying five spectrometers attached with TAP, LIF, LPET, LTAP and PET crystals. The protocol is applied to the xenotime grains of tonalite-trondhjemite-granodiorite-gneiss (TTG) rocks from the geochronologically well-constrained terrain of the Bundelkhand Craton, central India. The obtained xenotime age 2929$\pm$23 Ma of TTGs is in agreement with the earlier published Neoarchaen 2697$\pm$3 Ma Pb–Pb zircon ages from the same area which validates the authenticity of the analytical method developed at the BHU-EPMA facility.

      $\bf{Highlights}$

      $\bullet$ Analytical protocol for high precision U–Th–Pb chemical dating of xenotime by EPMA.

      $\bullet$ High precision ages from TTG gneiss of the Bundelkhand Craton, Central India.

      $\bullet$ Ages distinguishable from earlier reported ages from other techniques and samples.

      $\bullet$ Validates the authenticity of the analytical method developed at the BHU-EPMA facility.

    • Impact of SAPHIR radiances on the simulation of tropical cyclones over the Bay of Bengal using NCMRWF hybrid-4DVAR assimilation and forecast system

      DEVANIL CHOUDHURY ANKUR GUPTA S INDIRA RANI JOHN P GEORGE

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      Observing System Experiments (OSEs) were conducted to analyze the impact of assimilation of Megha-Tropique’s (MT) Sounder for Probing Vertical Profiles of Humidity (SAPHIR) radiances on the simulation of tracks and intensity of three tropical cyclones (Kyant, Vardah, and Maarutha) formed over the Bay of Bengal during 2016–2017 North Indian Ocean cyclone period. National Centre for Medium Range Weather Forecast (NCMRWF) Unified Model (NCUM) Hybrid-4DVAR assimilation and forecast system was used for the OSEs. Assimilation of SAPHIR radiances produced an improvement of 9% and 12%, respectively, in the cyclones’ central sea level pressure (CSLP) and the maximum sustained wind (MSW), while an improvement of 38% was seen in the cyclone tracks within the forecast lead time of 120 hrs. Initial assessment shows that the improvement in the cyclone intensity is due to the assimilation of the unique surface peaking channel of SAPHIR (channel-6), whereas the improvement in the cyclone track is due to the assimilation remaining five channels of SAPHIR. Thus, the assimilation of SAPHIR radiances in the NCUM system showed improvement in both intensity and track of the cyclones over the Bay of Bengal; however, more cyclone cases over different ocean basins have to be analyzed to make a robust conclusion. This study specifies the importance of similar microwave humidity instruments in the same frequency range for the detailed exploration of cyclone track and structure.

      $\bf{Highlights}$

      $\bullet$ Impact of SAPHIR humidity channel information in the NCMRWF Hybrid-4DVar assimilation and forecast system is analysed through Observing system experiments (OSEs)

      $\bullet$ Assimilation of SAPHIR humidity information improved both track and intensity of the cyclones compared to the control experiment, and the improvement is visible upto a lead time of 5 days

      $\bullet$ It is noted that the improvement in the cyclone intensity simulation is due to the assimilation of the lowest peaking channel of the SAPHIR, while the track improvement is contributed by other channels as well.

      $\bullet$ This study underlines the importance of SAPHIR like instruments in the low earth orbiting satellites with frequent revisit time to explore the features of cyclones.

    • Exploration and utilisation of groundwater resources in extreme arid regions of the Tibetan Plateau: A case study on Ali area, China

      KANG X B XU M LI K LIU X

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      Identifying a good site for groundwater exploitation in arid areas with scarce hydrogeological data is a challenging task. In this study, west of the Tibet Autonomous Region located at the peak of the world ridge that belongs to the extreme water-scarce poverty zone is used as the study area. This study is the first to determine the formation and controlling factors affecting the groundwater resources in Ali area via comprehensive geophysical and geochemical prospecting. The meteorological and hydrological characteristics of the study area are analysed, and the source and characteristics of water vapour in the study area are determined. Although the Indian peninsula and the Arabian Sea water vapour transmission paths exist, only small amounts of water vapour enter the area because of the distance limit and alpine barrier, which is the main reason for the drought in the study area. An overall conclusion of the hydrogeological condition and groundwater resources in Ali area is drawn on the basis of geophysical surveying, hydrogeological drilling, and water chemical analysis. The distribution of water resources in the Quaternary Aquifer, which is controlled by water vapour transport, aquifer-forming deposits, river distribution, and temperature, is not well-proportioned. The aquifer potentiality reduces from the southern to the northern direction in sequence. Thus, the great mass of midlands and the northern region belong to drought zones. Groundwater salinity, which is affected by drought, is higher than surface water salinity and obviously increases in constituent concentrations. The findings promote the understanding and utilisation of water resources in the study area.

      $\bf{Highlights}$

      $\bullet$ The study area located at the peak of the world ridge that belongs to the extreme water-scarce poverty zone.

      $\bullet$ This study is the first to determine the formation and controlling factors affecting the groundwater resources in Ali area via comprehensive geophysical and geochemical prospecting.

      $\bullet$ The distribution of water resources in the Quaternary Aquifer of Ali area, which is controlled by water vapour transport, aquifer-forming deposits, river distribution, and temperature, is not well-proportioned.

      $\bullet$ The water vapour originating from the Indian Peninsula and the Arabian Sea is blocked by high mountains, thereby minimising the amount of water vapour that can enter Ali and inducing less precipitation, which is the main reason for the drought in the study area.

    • Tectonic appraisal of the Mid-Thane Creek of Mumbai, India: An integrated geophysical approach

      JACOB J PITCHIKA V K DUBEY KM MISHRA A KUMAR P KUMAR S MAHALE V P CHAUBEY A K

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      Integrated geophysical surveys, comprising marine magnetic, high resolution shallow seismic and single-beam bathymetry were conducted to assess subsurface tectonics of the Mid-Thane Creek (MTC) of Mumbai. The bathymetry in the intertidal zone of MTC varies drastically due to periodic dredging, with maximum depth up to 6.4 m and a minimum of $\sim$−1.6 m. High resolution shallow seismic sections up to the depth of $\sim$35 m from the sea-floor are generated to analyze the neotectonic activity of the creek. Imprints of deep-seated lineaments are recognized from magnetic anomaly map of the MTC. To delimit lateral extent of the lineaments/faults, results of several derivative methods including tilt derivative and standard Euler deconvolution are merged with the selected crest value of the horizontal derivative. To estimate depth to the source, Euler deconvolution, tilt derivative, analytic signal, and source parameter imaging method have been used. However, the depth estimation for the lineaments/faults is highly discrepant for this region, because of the complex tectonics associated with the periodic emplacements of Deccan flood basalt. To confine the top and bottom boundary of this highly magnetized basaltic layer, we have carried out spectral analysis considering 18 windows of 2000 $\times$ 2000 m with an overlap of 500 m. The average depth to the top and bottom of the source body estimated using spectral analysis is consistent with the depth estimated from the derivative filters. This confirms that the lineaments identified by the derivative filters may embed in the basaltic layer of MTC. The most prominent lineament interpreted from the seismic and magnetic data, in the central region of MTC is inferred as the marine analogue of Alibagh–Uran Fault passing through the mainland of Alibagh and Uran close to Mumbai city.

      $\bf{Highlights}$

      $\bullet$Acquired, processed and interpreted high resolution shallow seismic, marine magnetic, single beam bathymetry data in the Mid-Thane creek of Mumbai, India.

      $\bullet$Neo-tectonic and deep-seated tectonic elements are identified using the seismic and magnetic data.

      $\bullet$Identification of the faults/lineaments and source depth estimation are performed using total horizontal, analytic signal, tilt derivative, Euler deconvolution and source parameter imaging derivative methods.

      $\bullet$Thickness of the flood basalt where the faults/lineaments are embedded is estimated using spectral analysis.

      $\bullet$Interpreting the marine extension of Alibagh–Uran fault zone in the Mid-Thane creek of Mumbai, India.

    • Water discharge and suspended sediment dynamics in the Chandra River, Western Himalaya

      AJIT T SINGH PARMANAND SHARMA CHIRAG SHARMA LALURAJ C M LAVKUSH PATEL BHANU PRATAP SUNIL OULKAR MELOTH THAMBAN

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      Glacier systems are important components of the hydrological cycle and a major source of meltwater and sediment flux that controls the river ecology, water quality, and hydropower generation in the Indian Himalayan Region (IHR). Thus, understanding short- and long-term changes in water and suspended sediment (SS) dynamics is crucial in highly sensitive pro-glacial Himalayan Rivers. In the present study, the Chandra River basin in Western Himalaya was chosen to study river discharge, SS transport dynamics, physical erosion rate, and their governing factors for the 2017 melting season (May–September). The daily mean water discharge and SS concentration in the Chandra River was 260.7 m$^{3}$ s$^{-1}$ and 775.5 mgL$^{-1}$ with maximum discharge and SS flux in the month of July. The air temperature showed significant relationship with the river discharge ($R^{2}$= 0.67; n = 156; p <0.001), which in turn controlled the SS export in the basin ($R^{2}$ =0.86; n = 130; p <0.001). An anticlockwise sediment-discharge hysteresis during peak flow conditions suggest exhausted sediments or large distance of sediment transport (>100 km) from the upper glacierized region to the end of the basin. Statistical analysis of SS particle size showed poorly sorted immature grains with a dominance of silt particles (85%), followed by sand (8.5%) and clay (6.5%). The SS estimates revealed a total suspended sediment yield of 1285 tons km$^{-2}$ yr$^{-1}$ and physical erosion rate of 0.47 mm yr$^{-1}$. Considering the socio-economic importance of the Himalayan region, the present study will help to evaluate the water and sediment budget of the Chandra River, Western Himalaya and to establish their relationship to the meteorological conditions in the basin.

      $\bf{Highlights}$

      $\bullet$The total water discharge and suspended sediment flux during ablation period (May–September 2017) in the Chandra River were 3536 MCM and 3 million tons.

      $\bullet$Overall, the suspended sediment were composed of silt size particles (85%) followed by sand (8.5%) and clay size (6.5+%) particles.

      $\bullet$The suspended sediment estimates revealed a total suspended sediment yield of 1285 tons km$^{3}$ yr$^{-1}$ and physical erosion rate of 0.47 mm yr$^{-1}$

      $\bullet$ This study will be useful in understanding the SS cycling from the Himalayan region and to build robust models for future projections.

    • Major ion, trace metal and environmental isotope characterization of groundwater in selected parts of Uddanam coastal region, Andhra Pradesh, India

      TIRUMALESH KEESARI ANNDASANKAR ROY DIKSHA PANT UDAY KUMAR SINHA NAGENDRA KUMAR P V L VAIKUNTA RAO

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      This paper elaborates the hydrochemical and environmental isotope ($\delta^{2}$H and $\delta^{18}$O) inferences obtained from Uddanam region, Andhra Pradesh, India. Groundwater samples collected during pre-monsoon (June 2019) showed that the quality is fresh (EC < 1539 $\mu$S/cm) and contaminants like fluoride (<1.6 mg/L) and nitrate (<49 mg/L) are present within permissible limits. The composite water quality indices for drinking (DWQI: 14.1–92.5) and irrigation (IWQI: 2.8–20.2) are found to be satisfactory. The major water types are found to be Ca–Na–HCO$_{3}$, Na–Ca–HCO$_{3}$, Na–Mg–HCO$_{3}$–Cl, Ca–Mg–HCO$_{3}$–Cl and Na–HCO$_{3}$. Three geochemical pathways are found signifying evaporite dissolution, contribution of silicate mineral weathering and base-exchange process, which is supported by estimated chloro-alkaline indices (CAI-1: −4.3 to −0.2, CAI-2: −1.03 to −0.08). Trace metal data clearly suggest that groundwater is free from any metal pollution. Dissolved silica (SiO$_{2}$) levels range from 34 to 131 mg/L and do not show any particular spatial trend. Isotope data infer that groundwater is recharged by rainwater after undergoing evaporation ($\delta^{18}$O: −6.0 per thousand), which matches with that of the combined isotope signature ($\delta^{18}$O: −5.5 per thousand) of SW and NE monsoon rainfall. $\delta^{18}$O–TDS correlations and hydrochemical facies evolution (HFE) diagram do not infer any seawater intrusion into these coastal aquifers.

      $\bf{Highlights}$

      $\bullet$ The composite water quality indices infer good to excellent category for drinking and agriculture.

      $\bullet$ Mineral weathering, evaporite dissolution and base-exchange reactions are the main geochemical processes.

      $\bullet$ Dissolved silica occurrence in groundwater is sporadic.

      $\bullet$ Isotope indicators show the signature of both SW and NE monsoons recharge to groundwater.

      $\bullet$ Observed brackishness in groundwater is due to water – rock interaction and not due to sea water intrusion.

    • Geo-informatics based multi-criteria decision analysis (MCDA) through analytic hierarchy process (AHP) for forest fire risk mapping in Palamau Tiger Reserve, Jharkhand state, India

      BINITA KUMARI ARVIND CHANDRA PANDEY

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      Forest fires constitute a foremost environmental calamity that distresses the sustainability of the forest. The main source of degradation of Jharkhand forests are forest fires conquered by forest species of Sal and Bamboo. Palamau Tiger Reserve in Jharkhand state, India, is becoming more susceptible to forest fire due to anthropogenic disturbance coupled with speedy upsurge in population. In this study, forest fire risk in PTR was evaluated based on various fire inducing factors, viz., forest fuel, settlements, roads, bare soil index, elevation slope and aspect. Geoinformatics based multi-criteria decision analysis (MCDA) through method of AHP (analytic hierarchy process) used to extract forest fire risk map in five classes: Very low risk, low risk, moderate risk, high risk and very high risk. The results obtained showed that about 180 km$^{2}$ (14.85%) falls under very low fire risk zone, 234 km$^{2}$ (19.30%) falls in low fire risk zone, 269.73 km$^{2}$ (22.16%) falls under moderate fire risk zone, 299.36 km$^{2}$ (24.59%) falls under high fire risk zone and 232.56 km$^{2}$ (19.10%) falls in very high fire risk zone. Forest fire risk map was validated from historical fire incidents observed through field data, MODIS and SNPP-VIIRS satellite products. The results showed that the geoinformatics based forest fire risk zones delineated through MCDA-AHP method are in good agreement with historical forest fire occurrences, henceforth may be utilised for fire planning for mitigation in forest areas.

      $\bf{Highlights}$

      $\bullet$PTR is becoming more susceptible to forest fire due to anthropogenic disturbance coupled with speedy upsurge in population.

      $\bullet$Forest Fires Risk was evaluated based on various fire inducing factors viz., forest fuel, settlements, roads, bare soil index, elevation slope and aspect through method of AHP.

      $\bullet$Forest fire risk map was validated from historical fire incidents observed through field data, MODIS and SNPP-VIIRS satellite products.

      $\bullet$The results showed that the geoinformatics based forest fire risk zones are in good agreement with historical forest fire occurrences henceforth may be utilised for fire planning for mitigation in forest areas.

    • Estimation of hydraulic conductivity in fractured crystalline aquifers using remote sensing and field data analyses: An example from Wadi Nasab area, South Sinai, Egypt

      AHMED EL-RAYES ADEL OMRAN GERIESH MOHAMED VOLKER HOCHSCHILD

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      Fractured crystalline aquifer is considered as the main source of water supply in most of the arid and semi-arid regions. Fractures play an essential role as pathways through which groundwater flows from high catchments to supply the productive wells in lowlands. The hydraulic conductivity measurements for highly fractured crystalline aquifers are a must for optimal management of groundwater extraction from these aquifers. The current work aims at estimating the hydraulic conductivity of the crystalline aquifer by using an unconventional approach based entirely on the processing of remotely-sensed lineament data and field observations. Extracted lineaments at four sites near the productive wells along Wadi Nasab area (WNA) were traced from Landsat (ETM+7) and other ancillary geological data by using image processing and GIS tools. Hence, four discrete fracture networks (DFN) were designed and practiced for the selected test sites to model the groundwater flow through the fracture system in order to estimate the hydraulic conductivity of the investigated crystalline aquifer. The achieved results indicated that the hydraulic conductivity of fractured basement aquifer of WNA varied between 2.3 $\times$ 10$^{-7}$ and 6.1 $\times$ 10$^{-7}$ m/s. The estimated hydraulic conductivity values are close to the values of previous field infiltration tests in the nearby area at Sinai. The previously estimated infiltration rates (expressing the vertical hydraulic conductivity) on the fractured crystalline outcrops ranged between 2.6 $\times$ 10$^{-6}$ and 6.5 $\times$ 10$^{-7}$ m/s, which are concordant with achieved results. Moreover, the achieved values match the previously published values of hydraulic conductivity for similar crystalline aquifers around the world, reflecting the high validity of the used unconventional, low-cost approach to estimate the hydraulic conductivity of fractured crystalline aquifers. The designed approach can be potentially practiced on similar basins in Sinai peninsula and other comparable basins having similar geological and climatic environments around the world.

      $\bf{Highlights}$

      $\bullet$ Estimating the hydraulic conductivity of fractured crystalline aquifer by using remotely sensed lineament data and field observations.

      $\bullet$ Discrete fracture networks (DFN) models the groundwater flow to estimate the hydraulic conductivity of the crystalline aquifer.

      $\bullet$ The estimated hydraulic conductivity values are varied between 2.3 $\times$ 10$^{-7}$ m/s and 6.1$\times$10$^{-7}$ m/s, which come in agreement with the previously estimated values using the conventional infiltration tests.

      $\bullet$ The results reflect the validity of using this unconventional and low-cost approach to estimate the hydraulic conductivity of fractured crystalline aquifers.

    • Geophysical and hydrochemical studies for sustainable development of groundwater resources in northwestern part of Telangana State, India

      SAKRAM GUGULOTHU RATNAKAR DHAKATE SREEDHAR K RAMESH A PRAVEEN RAJ SAXENA

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      Studies have been carried out to assess groundwater potential using geophysical analysis and water quality indices in parts of Nyalkal and Zaheerabad Mandal, Medak District, Telangana State. As a part of the study, 50 groundwater samples were collected and 103 Vertical Electrical Soundings (VES) had been carried out. The water quality was assessed with respect to various major ion chemistry and trace elements. It is found that major ions and trace elements are within the permissible limits, except Al, Pb, and Zn metals, which slightly exceeded beyond permissible limits. However, the results of VES reveal that in some parts of the study area, the resistivity range for topsoil (26.61–930 $\Omega$m), lateritic zone (453–738 $\Omega$m), clayey/sandy clay layer (4.71–94.2 $\Omega$m), weathered/fractured bedrock (60.5–928 $\Omega$m) and weathered/vesicular/massive basalt (8.05–676 $\Omega$m) are found with the formation of thick overburden and fractured basement. It is also found that the groundwater prospects are moderate to high depending on the extent of the weathering zone.

      $\bf{Highlights}$

      $\bullet$ Geophysical investigations were carried out to decipher the aquifer geometry and potential zones.

      $\bullet$ Groundwater quality for major and trace elements were carried out and compare with WHO standards.

      $\bullet$ An integrated analysis was made for sustainable development of groundwater resources.

    • Hydrological evaluation of global gridded precipitation datasets in a heterogeneous and data-scarce basin in Iran

      KHOSHCHEHREH M GHOMESHI M SHAHBAZI A

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      Accurate estimation of the precipitation characteristics, including the value, temporal pattern, and spatial distribution, plays a significant role in the input uncertainty reduction for rainfall-runoff models. In many basins, the improper spatial distribution of rain gauge stations or their limited historical recorded data causes many challenges, especially in heterogeneous catchments which due to the impact of the drastic geographical alterations on the rainfall distribution pattern, the cover of the ground stations cannot estimate the actual precipitation rate. This challenge can be potentially solved by adopting rainfall products as alternative or complementary data sources. In this research, three rainfall products (PERSIANN-CCS, CMORPH and ERA-Interim), were compared against rain gauge stations for calibration of a daily conceptual lumped rainfall-runoff model (CRFM) in a data-scarce and heterogeneous basin located in southwestern Iran. The results indicated that ERA-Interim has the best performance among other datasets. Better performance of this dataset compared to the in-situ data also suggests a better estimation of the basin average as well as the temporal pattern of precipitation. The KGE value was obtained as 0.8 and 0.74, respectively, for a rainfall-runoff model that utilized the ERA-Interim as input in the calibration and validation periods. The results showed that the performance of satellite-based data of CMORPH and PERSIANN-CCS is not acceptable in simulating the daily flow. Also, the seasonal assessment showed that ERA-Interim has a better performance compared to other datasets, during fall and winter. However, in the spring, the performance of all datasets significantly reduces, and the range of BIAS variation increases. Generally, all datasets were shown to perform better in simulating the flow in terms of the transition from dry to wet periods, rather than wet to dry periods.

      $\bf{Highlights}$

      $\bullet$ Three rainfall products (PERSIANN-CCS, CMORPH and ERA-Interim), were compared against rain gauge stations for calibration of a daily conceptual lumped rainfall-runoff model in a data-scarce and heterogeneous basin located in southwestern Iran

      $\bullet$ ERA-Interim has the best performance among other datasets and suggests a better estimation of the basin average as well as the temporal pattern of precipitation

      $\bullet$ The performance of satellite-based data of CMORPH and PERSIANN-CCS is not acceptable in simulating the daily flow

      $\bullet$ The performance of all datasets significantly reduces in spring

      $\bullet$ All datasets were shown to perform better in simulating the flow in terms of the transition from dry to wet periods, rather than wet to dry periods

    • Simulating hydrological response of a monsoon dominated reservoir catchment and command with heterogeneous cropping pattern using VIC model

      MINOTSHING MAZA ANKUR SRIVASTAVA DEEPAK SINGH BISHT NARENDRA SINGH RAGHUWANSHI ARNAB BANDYOPADHYAY CHANDRANATH CHATTERJEE ADITI BHADRA

      More Details Abstract Fulltext PDF

      Present study assesses the effect of finer land-use classification in simulating the rainfall-runoff response of Kangsabati reservoir catchment (3,627 km$^{2}$) and command (7,112 km$^{2}$) by considering cropland heterogeneity in variable infiltration capacity (VIC) model. High resolution LISS-IV satellite imageries were used for the land-use classification. Global sensitivity analysis was performed using VIC-ASSIST to identify the most and least influential parameters based on the sensitivity index of elementary effects. A fully distributed calibration approach was employed using 16 (detailed) and 8 (lumped) vegetation classes. Low flows during lean periods were over-estimated and peak flows were under-estimated by both the model setups at Kangsabati reservoir site. Detailed land-use classification resulted in the reduction in streamflow over-estimation (Percent Bias (PBIAS) from −20.99 to −14.41 during calibration and from –22.83 to –7.17 during validation) at daily time step. It further demonstrates the improvement in simulating the peak flows; hence, highlighting the importance of detailed land-use classification for vegetation parameterization in VIC model setup. River discharge regulation at Kangsabati reservoir resulted in poor model performance at Mohanpur, downstream site of Kangsabati reservoir. Therefore, calibration for Mohanpur was performed after updating the VIC simulated streamflow with routed reservoir spillage using Hydrologic Engineering Center-River Analysis System (HEC-RAS) model. Streamflow updation employing HEC-RAS at Mohanpur improved the modelling efficiency (Nash–Sutcliffe efficiency (NSE) from 0.50 to 0.65 during calibration and from 0.55 to 0.67 during validation) and reduced bias (PBIAS from 6.25 to –2.23 during calibration and from 15.06 to 7.40 during validation) considerably for daily flows. Model performance with reasonable accuracy was achieved at both the calibration locations which demonstrates the potential applicability of VIC model to predict streamflow in the monsoon dominated Kangsabati reservoir catchment and command.

      $\bf{Highlights}$

      $\bullet$LISS-IV satellite imageries were classified using ground truth survey data obtained for different crop types in the study area.

      $\bullet$Crop specific vegetation parameterization was used in setting up VIC modeling framework.

      $\bullet$Modeling efficacy was assessed for two vegetation parameterization schemes using single crop type and multiple crops.

      $\bullet$Global sensitivity analysis and fully distributed automatic calibration was performed using VIC-ASSIST software package.

      $\bullet$Utility of HEC-RAS was shown in routing reservoir spillage to the downstream gauging point in VIC modeling framework in the absence of integrated reservoir module.

    • Hydrogeochemical characteristics and water quality of Aji-Chay river, eastern catchment of Lake Urmia, Iran

      MORTEZA SAFARI ARDESHIR HEZARKHANI SEYYED REZA MASHHADI

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      The Aji-Chay river is the most important river discharging into endangered Lake Urmia in NW of Iran. The present study investigates the hydrogeochemical characteristics and origin of dissolved ions in the Aji-Chay river and some of its tributaries passing through Tabriz plain which is located at the east side of Lake Urmia. For this purpose, 317 water samples were collected during 9 years (2005–2014) from four stations and clustered to nine groups using K-means algorithm. Major cations and anions were considered to distinguish the hydrogeochemical evolution of water. The Piper, Langelier–Ludwig and Stiff diagrams classified water samples into predominant Na–Cl endmember and Ca–HCO$_{3}$ only in the upstream zone. With respect to Gibbs diagrams, mineral saturation indices and geology of the area, water chemistry of the Aji-Chay river reflects that water–rock chemical interactions including dissolution/precipitation of carbonate and sulfate minerals known as dedolomitization and dissolution of evaporitic salts along the flow path are the dominant factors controlling the water chemistry; furthermore, evaporation, silicate weathering, and ion exchange reactions change the chemistry of water to some extent. Overall, water quality is evaluated as poor. Furthermore, intense halite dissolution increases Na concentration in water which in turn reduces its suitability for irrigation purposes.

      $\bf{Highlights}$

      $\bullet$Hydrogeochemical characteristics of main branches of Aji-Chay river are examined through a long-term (9 years) sampling program; then, K-means algorithm is used to cluster the data into 9 groups

      $\bullet$Mineral saturation indices based on the concentration of ionic components in the water were calculated using PHREEQC software at the same thermodynamic conditions of gathered samples

      $\bullet$Several Indices and standard diagrams are utilized to delineate hydrochemical processes that dominate surface water and assess the influence of possible water-rock interactions on water chemistry

      $\bullet$Dissolution/precipitation of carbonate and NaCl-bearing lithological units substantially influence the quality of water

      $\bullet$The suitability of water is characterized as “poor” for irrigation purposes because of high Na concentration and salinity except in the upstream where lithology has not reduced the water quality

    • Geochemistry of calc-silicate rocks around Lunavada region, NE Gujarat: Implications for their protolith, provenance and tectonic setting

      GAYATRI N AKOLKAR MANOJ A LIMAYE

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      In this work, the calc-silicate rocks affiliated to the ‘Kadana Formation’, a youngest formation of the Lunavada Group have been investigated. These rocks are found to be embedded within associated rock types, viz., quartzites and metapelites in the form of isolated lensoidal bodies. Contact metamorphic textures and the typical mineral assemblage, viz., Act +Di + Cal + Qtz + Ttn $\pm$ Mc $\pm$ Pl $\pm$ Bt $\pm$ Ep $\pm$ Scp $\pm$ Chl with minor proportion of apatite, zircon and opaques can be observed in these calc-silicates. Major oxides, trace and rare earth elements were analysed to investigate the protolith type, provenance and tectonic setting of these rocks. Protolith must be calcareous sandstone with varied proportion of clay and deposited in shallow water environment as revealed by CaO, Al$_{2}$O$_{3}$ and FeO+MgO and Al–Zr–Ti ternary diagram, respectively. Low to moderate weathering of source rocks has been indicated by A–CN–K ternary diagram. Th/Sc vs. Zr/Sc and Th/Co vs. La/Sc plots confirm the continental source with felsic nature for these rocks and the calc-silicate samples fall within the active continental margin region of Sc–Th–Zr/10 diagram which also justify the kind of provenance for primary sediments.

      $\bf{Highlights}$

      $\bullet$The calc-silicate rocks show major oxides, trace and rare earth element compositions which are very similar to those of their post-archean counterparts. Similarly, in the REEs vs. sample/REE chondrite normalized pattern, a moderate negative Eu anomaly is observed; these observations suggest that the chemical composition of the continental crust of the study area was similar to that of the post-archean continental crust.

      $\bullet$Data plotted in Al$_{2}$O$_{3}$, CaO and FeO + MgO diagram of Barton et al. (1991) indicated that the protolith of calc-silicate rocks of the study area is calcareous sandstone with small and varied amounts of clay within it, as most of the samples fall within or very close to the greywacke zone.

      $\bullet$CIA studies are pointing towards the low to moderate weathering of the source under the cold and arid conditions.

      $\bullet$The Th–Sc characteristics (Th/Sc > 1) support a predominantly continental source for these rocks; similarly, values of Zr/Sc indicate a moderate amount of sediment recycling.

      $\bullet$Higher abundances of incompatible elements imply predominantly felsic rocks in the source, which is also supported by LREE-enriched patterns. As per the Th/Co vs. La/Sc plot, mostly of granitic (felsic) composition is inferred for primary sediments for these calc-silicate rocks.

      $\bullet$The study concludes that the primary sediments for the calc-silicates of the Lunavada Group were deposited in an active continental margin setting.

    • Understanding the interactions between meteorological and soil moisture drought over Indian region

      PRABIR KUMAR DAS SUSHANT CHANDRA DILIP KUMAR DAS SUBRATA KUMAR MIDYA ARATI PAUL SOUMYA BANDYOPADHYAY VINAY KUMAR DADHWAL

      More Details Abstract Fulltext PDF

      The present study aims at analysing the relationship between meteorological and soil moisture droughts over different meteorological regions of India based on change-point, trends and probability analysis. The long term gridded standardized-precipitation-evapotranspiration-index (SPEI) and standardized-soil-moisture-index (SSMI) data during 1980–2015 were used to address the meteorological and soil-moisture drought, respectively. The significant changes in the time-series SPEI and SSMI data at different time-scales were estimated using Pettitt’s test. The variations in change-points among different time-scales of SSMI were much lower than SPEI, specifically in parts of NW and central India. The inter-annual variability of drought parameters, i.e., duration and magnitude, showed good agreement between meteorological and soil moisture droughts for mild drought conditions. However, under moderate drought conditions, the behaviour of meteorological and soil moisture drought was different, specifically over peninsular India. The trend analysis revealed that SSMI based drought occurrences were significantly decreasing over all the four meteorological regions, whereas in case of SPEI, significant trends were observed only over peninsular India for mild drought condition. The probability of occurrences of both meteorological and soil moisture droughts were higher over major parts of India in case of mild droughts, whereas the values were lower for moderate drought conditions.

      $\bf{Highlights}$

      $\bullet$The Pettitt’s change point analysis revealed that variations of the period of significant changes among different time scale SSMI was much lower comparison to SPEI.

      $\bullet$In major parts of the country, good agreement between SPEI and SSMI derived drought parameters, i.e., duration and magnitude, were observed for mild drought conditions. However, it was quite low in moderate drought conditions, more specifically over peninsular and central India.

      $\bullet$The trend analysis revealed that the soil moisture drought was decreasing during the study period. Similar observations were recorded in meteorological drought also, but with some increasing drought duration and magnitude in parts of NW and NE India.

      $\bullet$The probability of occurrences of both meteorological and soil moisture droughts were higher over major parts of India in case of mild droughts, whereas the values were lower for moderate drought conditions.

    • On deriving influences of upwind agricultural and anthropogenic emissions on greenhouse gas concentrations and air quality over Delhi in India: A stochastic Lagrangian footprint approach

      THEERTHA KARIYATHAN DHANYALEKSHMI PILLAI ELDHO ELIAS THARA ANNA MATHEW

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      Delhi, the capital city of India witnesses severe degradation of air quality and rapid enhancement of trace gases during winter. Still it is unclear about the relative role of the meteorological conditions and the post-monsoon agricultural stubble burning on the occurrence of these events. To overcome this, we examine the use of applying high-resolution transport model to establish the link between atmospheric concentrations and upstream surface fluxes. This study reports the implementation of a Lagrangian approach and demonstrates its capability in deriving the upwind influences over Delhi. We simulate stochastic back trajectories over Delhi by implementing stochastic time-inverted Lagrangian transport (STILT) model, driven by the meteorological fields from the European Centre for Medium Range Weather Forecasts (ECMWF) model. During the post-monsoon, when mixing layer height is shallow, we find high near-field influence. The variations in footprint simulations with receptor heights show the effect of mixing layer dynamics on the air-parcels. By using atemporal emission fields, we find a considerable impact of meteorological conditions during November that contributes to the enhancements of trace gases. Together with strong emissions (anthropogenic and biomass burning), these enhancements can be several orders higher compared to other seasons. Through the receptor-oriented STILT implementation over India, we envision a wide range of applications spanning from air quality to climate change. An advantage of this implementation is that it allows the use of pre-calculated footprints in simulating any trace gas species and particulate matter, making it computationally less demanding than running an ensemble of full atmospheric transport model.

      $\bf{Highlights}$

      $\bullet$ Our study elaborates a method to estimate the near-field influences on a region of interest or receptor location (Delhi), which is pivotal in devising mitigation strategies to curb the increasing pollution events (one of the country's greatest concerns). For this, we implement STILT that uses ECMWF meteorological data to generate simulations of realistic atmospheric trajectories and footprints to the Indian subcontinent domain. From this data, the influence matrix is derived.

      $\bullet$We demonstrate the usefulness of the STILT modeling framework by deriving air-parcel trajectories and footprint over Delhi, which shows a higher influence of Haryana and Punjab region as upwind location to Delhi during the pre-monsoon and post-monsoon season.

      $\bullet$We highlight the importance of proper accounting of vertical mixing in the atmospheric model by simulating footprint and trajectory measurements at different heights. This shows that during postmonsoon when PBL height is shallow there is a higher influence function thus choking Delhi in the winter.

      $\bullet$Our analysis shows the usefulness of pre-calculated footprints in simulating any trace gas species and particulate matter concentration thus saving a lot of computational costs incurred. This is illustrated by generating concentration signals using EDGAR global inventory for CO and CO$_{2}$ emissions from biomass burning and CO$_{2}$, CO, N$_{2}$ O and CH$_{4}$ from anthropogenic emissions. We observed concentration enhancement in agreement with the diurnal PBL dynamics (higher in lower layers (20 m) compared to higher layers (500 m)).

      $\bullet$We envision extending the STILT network to have wider insights on regional and local fluxes of CO$_{2}$, CO, and CH$_{4}$. The study can be improvised by utilizing hourly-varying emission fluxes and also by accounting for other sources of emissions.

    • Ambient noise and earthquake HVSR modelling for site characterization in southern mainland, Gujarat

      DURGADA NAGAMANI SIVARAM K PURNACHANDRA RAO N SATYANARAYANA H V S

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      This study provides the assessment of site characterization and possible shallow shear-velocity structure from the study of the horizontal to vertical spectral ratio (HVSR) measurements using the ambient noise or microtremor (herein called classical HVSR), extracted Rayleigh wave from the ambient noise data (herein called standard HVSR) and earthquake (herein called earthquake HVSR) data at five stations in the Surat district of mainland Gujarat, India. These locations are the hub of many mining and industrial projects like oil and natural gas, which need to function safely within the seismic hazard and ground shaking limits. From the classical and standard HVSR datasets, estimates of the predominant resonant frequency of the soil are obtained, observed to be well matched, from which first order inversions are carried out around the predominant frequency to provide a fair estimate of thickness of the regimented layer over a hard seismic substratum up to a depth of 100 m. In the standard HVSR datasets, the Rayleigh wave ellipticity curves are extracted with time–frequency analysis using continuous wavelet transforms. This is followed by the Rayleigh wave ellipticity inversion approach to derive a first order approximate sedimentary shear velocity structure. We also compute HVSR measurements using earthquakes. The noise and earthquake HVSR curves are well-matched in terms of the predominant frequencies and range from 3.8 to 16.7 Hz and 3.2 to 16.5, respectively. The estimated V$_{\rm{S30}}$ values (the average shear wave velocity (V$_{\rm{S}}$) for the top 30 m of the soil) vary from 520 to 1350 m/s, matching well with some of the geotechnical studies conducted here. The study emphasizes the effectiveness of the single station HVSR method in determination of hitherto unknown soil structures as economical and non-invasive exploration viability and proving quite useful for critical centres of industrial establishments.

    • On the dynamics of cyclogenesis, rapid intensification and recurvature of the very severe cyclonic storm, Ockhi

      SANAP S D MOHAPATRA M ALI M M PRIYA P VARAPRASAD D

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      A very severe cyclonic storm (VSCS), ‘Ockhi’ started its journey from southwest Bay of Bengal (BoB) over Comorin area (7.5$^{\circ}$N–77.5$^{\circ}$E) as a low-pressure area on 28 November, 2017. Initially it moved north-westwards across Lakshadweep Islands without hitting Tamil Nadu or Kerala coast, then moved north-eastward over the Arabian Sea and dissipated upon hitting south Gujarat coast on 06 December, 2017. Rapid intensification (RI), clockwise recurvature and a longer track were the major features of the VSCS, Ockhi. In the present study, an attempt has been made to understand the mechanism of cyclogenesis, RI and recurvature of the Ockhi using satellite and reanalysis datasets. Initially, role of easterly waves (EW) and Madden Jullian Oscillations (MJO) on the cyclogenesis of tropical cyclone Ockhi is addressed. Our analysis suggests that the EW (MJO) played a seminal (insignificant) role in preconditioning the atmosphere for the cyclogenesis of the Ockhi. Our detailed analysis using various oceanic parameters indicate that, the passage of the cyclonic storm over the regions of high thermal energy, especially warmer ocean mean temperature (OMT) at 100 m depth, was instrumental in its rapid intensification. Further, we addressed the recurving feature of the VSCS Ockhi using steering flow analysis. It is found that strong north-eastward steering winds, embedded in subtropical westerlies with deep southward extent, favoured the recurving of the Ockhi towards north-eastward by suppressing the conventional westward (north-westward) track movement.

      $\bf{Highlights}$

      $\bullet$Easterly wave activity facilitated the cyclogenesis.

      $\bullet$Upper ocean thermal energy contributed in rapid intensification.

      $\bullet$Trough in upper level westerlies facilitated in recurvature of the VSCS Ockhi.

    • Evaluating the seismic hazard in the Kachchh Region, western India using the river gradient length anomaly technique

      RAJ SUNIL KANDREGULA GIRISH CH KOTHYARI GAURAV CHAUHAN VASU PANCHOLI SWAMY K V ABHISHEK LAKHOTE SNEHA MISHRA THAKKAR M G

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      In the present study, we assess seismic hazard potential and surface deformation pattern along and across the strike of major active faults in the intra-plate Kachchh Rift Basin (KRB). Towards this, we adopted river Gradient Length Anomaly (GLA) technique, which detects recent tectonic deformation along a river profile on local and regional scales. The major deviations along the river profile can be correlated with exogenic (erosion/sedimentation/anthropogenic) and endogenic (active tectonic movement) processes. We analysed 130 river profiles for GL anomalies, over an area of ${\sim}$26,700 km$^{2}$ in the KRB to identify possible locations that have undergone active tectonic deformation associated with the fault movement. The acquired results show that the higher magnitude negative GL anomalies (uplift) are observed proximal to the fault zones. Our estimates reveal that, around 13% of the study area falls under high tectonically active zone, around 27% of the area falls under moderately active zone, while 60% of the area shows very low or negligible tectonic activity. The estimated results of the GL anomalies are compared with the existing double-difference tomograms, to understand the role of subsurface fault dynamics on the GL anomalies. Furthermore, the results of GLA are correlated with the existing results of the peak ground acceleration (PGA) values of the basin, in order to obtain the precise information regarding surface deformation and site-specific ground acceleration for accurate assessment of seismic hazard.

    • Future changes in rice yield over Kerala using climate change scenario from high resolution global climate model projection

      STELLA JES VARGHESE SAJANI SURENDRAN AJITHKUMAR B KAVIRAJAN RAJENDRAN AKIO KITOH

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      The impact of climate change on agricultural yield is one amongst the major concerns the world is witnessing. Our study focusses on rice yield prediction for an agricultural research station in Kerala with the help of climate change scenario input from the Meteorological Research Institute (MRI) Global Climate Model (GCM) projection under Representative Concentration Pathway 8.5 (RCP8.5). We have used Cropping System Model (CSM) Crop Estimation through Resource and Environment Synthesis (CERES) Rice within Decision Support System for Agrotechnology Transfer (DSSAT) package for predicting the yield. Our study has the novelty of using very high-resolution climate data from a model which is highly skilful in capturing the present-day climate features and climatic trends over India (in particular, over the Western Ghats), as input for simulating the future crop yield. From this study, we find that the rice yield decreases due to rise in temperature and reduction in rainfall, thereby reducing the crops maturity time in the future. Based on our results, the adaptation measures suggested to achieve better yield under future warming conditions are: (i) to opt for alternative rice varieties which have tolerance to high temperatures and consume less water, and (ii) shifting of planting date to the most appropriate window.

      $\bf{Highlights}$

      $\bullet$Impact study of future climate change on rice yield is carried out using CERES Rice Cropping System Model after systematic validation.

      $\bullet$Highly reliable climate change information from the projection by a 20-km resolution global climate model of MRI which is remarkably skilful in simulating the present-day Indian climate, is used as input for the crop model.

      $\bullet$Rice yield is found to decrease in future due to rise in temperature and reduction in rainfall, thereby reducing the crops maturity time.

      $\bullet$Adaptive measures of opting for temperature tolerant, high yielding rice varieties which consume less water and shifting of planting date to an appropriate window, are suggested to achieve better yield.

    • Role of site effect for the evaluation of attenuation characteristics of P, S and coda waves in Kinnaur region, NW Himalaya

      RICHA KUMARI PARVEEN KUMAR NARESH KUMAR SANDEEP

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      The site effect and attenuation studies are carried out for Kinnaur region of northwest Himalaya, India. A total of 109 local events happened in Kinnaur region of magnitude range 1.6–4.5, are utilized for present work. The earthquake records are influenced by the site effect depending on soft sediment thickness beneath the recording sites. Therefore, in the present study, records are corrected for site effects to estimate P ($Q_{p}$), S ($Q_{s}$) and coda ($Q_{c}$) wave quality factor. The regional frequency dependent attenuation relations, i.e., $Q_{p}$(f)$=$(29$\pm$1)$f^{(1.01±0.05)}$, $Q_{s}$ (f)$=$(38$\pm$5)$f^{(1.1±0.06)}$ and $Q_{c}$(f)$=$(74$\pm$11)$f^{(1.17±0.01)}$ are established for the Kinnaur region. The Kinnaur Himalaya mainly belongs to Higher Himalaya Crystalline (HHC) and Tethys Himalaya, where these two geological units are differentiated by the South Tibetan Detachment System (STDS). The resonance frequencies and attenuation characteristics are estimated for both regions, i.e., HHC and Tethys Himalaya. A comparison is made between HHC and Tethys Himalaya in the form of resonance frequencies and attenuation properties. The low value resonance frequency and high rate of attenuation towards the northern side of STDS, i.e., Tethys Himalaya support the presence of low-grade metasedimentary rocks. It suggests that Tethys Himalaya has high seismic hazard potential zone compared to HHC.

      $\bf{Highlights}$

      $\bullet$Site effects have been incorporated to estimate attenuation characteristics of P, S and coda waves in Kinnaur region, NW Himalaya.

      $\bullet$The regional frequency dependent attenuation relations i.e., $Q_{p}$(f)=(29$\pm$1)$f^{(1.01±0.05)}$, $Q_{s}$ (f)=(38$\pm$5)$f^{(1.1±0.06)}$ and $Q_{c}$(f)=(74$\pm$11)$f^{(1.17±0.01)}$ are established for the Kinnaur region. The close resemblance of resonance frequencies with the geology of the study region has been observed.

      $\bullet$The Tethys Himalaya lies in present study region has high seismic hazard potential zone as compare to Higher Himalaya Crystalline.

    • Evaluation and hydrological impact of land-use changes in the Longtan basin

      GUIYAN MO YONGXIANG ZHANG YA HUANG CHONGXUN MO QING YANG

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      Compared to climate change, land-use changes were the main driving factors to short-term hydrological variety. To evaluate land-use types variation and quantify its hydrological impact, this paper identified the temporal-spatial features and simulated the hydrological process of different land-use types over the last two decades (1990–2010) based on the soil and water assessment tool (SWAT). Meanwhile, the possible influence of land-use changes on streamflow in the next 30 years (2020–2050) was also considered. Results indicated that (1) land-use types mainly constituted of forest land, grassland and cultivated land, which had the largest decreasing rate of 17.34 km$^{2}$/10a. At the same time, inter-conversion mainly conducted among the main land-use types and had a similar transfer structure for these two sub-periods (1990–2000, 2000–2010) during 1990–2010, with a more dramatic transformation in 2000–2010. (2) Simulated annual and monthly surface runoff did not vary greatly from 1990 to 2010 and presented a relatively uniform monthly distribution. At the same time, the increased vegetation coverage (forest land and grassland) can not only reduce surface runoff but also prevent peak flood with increasing and decreasing steeply. (3) Finally, hydrological variability to the future land-use change will not be intensive, which possibly related to the undeveloped regional economic and insignificant human activities. But it also needed some measures to maintain a balanced nature, such as the soil and water conservation measures and returning cultivated land to forest land and grassland.

      $\bf{Highlights}$

      $\bullet$Identifying land-use variation characteristics from 1990 to 2010.

      $\bullet$Calibrating and validating a satisfactory soil and water assessment tool (SWAT) for surface runoff simulation.

      $\bullet$Quantifying the hydrological response to the past land-use change.

      $\bullet$Predicting how different land-use scenarios affected streamflow.

      $\bullet$Experiment in the karstic basin, which is lack of related research.

    • Characteristics of extreme precipitation in South China during April–July for early rice season

      LIJI WU FEI HU LI XIE

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      Extreme precipitation has significant impacts on human society and agriculture development under global climate change as well as severe effects on rice development. However, little research has been done on the characteristics of extreme precipitation in different rice growth stages. Taking the South China region as a case study, the characteristics of extreme daily precipitation in the early rice season (April–July) from 1960 to 2009 were investigated by using percentile method. Results indicated that extreme precipitation threshold increases since the tillering stage, and there is big difference between the first and the rest growth stages. Extreme precipitation is serious in the eastern part than in the western part of South China during the seeding and tillering stage, and reverse since the booting stage. Frequency of extreme precipitation increases in recent decades after the booting stage. Finally, flood risk regions form more easily in the coastal cities and the western part of South China in the 1990s and 2000s since the tillering stage.

      $\bf{Highlights}$

      $\bullet$ Extreme precipitation has significant impact on the rice production in South China region during the early rice period. However, characteristics of extreme precipitation in different rice growth stages are still unclear. The researchers use daily precipitation data (1960–2009) and percentile method to analysis the extreme precipitation distribution in South China region during April–July for early rice season.

      $\bullet$ The researchers found extreme precipitation is serious in South China region since tillering stage, and getting more serious when it comes to the rest of the growth stages. High extreme precipitation centers occur in different region during early rice period. Flood protection and crops planning should focus on different region for different stages. Data analysis also show that extreme precipitation is serious in the eastern part than in the western part of South China during the seeding and tillering stage, and reverse since the booting stage. Frequency of extreme precipitation increases in recent decades and more flood risk region form in the coastal cities. Crop planning and disaster managements in South China during early rice period need for careful consideration of different flood risk region in different stages.

    • Evaluation of WRF and artificial intelligence models in short-term rainfall, temperature and flood forecast (case study)

      EMADEDDIN SHIRALI ALIREZA NIKBAKHT SHAHBAZI HOSSEIN FATHIAN NARGES ZOHRABI ELHAM MOBARAK HASSAN

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      Flood prediction is very critical for efficient use of flood control reservoirs, and earthen and concrete levees systems. As a result, flood prediction has a great importance in catchment areas. In this study, rainfall and air temperature were predicted in Karun-4 basin in southwest of Iran by using three different models including WRF numerical model, ANN, and SVM model in order to evaluate accuracy in flood forecasting. The rainfall and air temperature prediction and flood forecasting results using different schemas of WRF model indicated that MYJLG schema has more accuracy than other schemas. Partial mutual information (PMI) algorithm was used in order to determine the effective input variables in ANN and SVM models. The results of using PMI algorithm showed that rainfall at rain gauge stations in the next 6 hrs indicated that the effective variables included relative humidity, current rain status (present rainfall), rainfall in 6 hrs ago, and rainfall and temperature of 12 hrs ago. Also, the PMI algorithm results for predicting air temperature in the next 6 hrs showed that the effective input variables including the temperature of 18 hrs ago, current temperature, temperature of 12 hrs ago, and temperature of 6 hrs ago. The comparison between the peak discharge and runoff height values of the predicted flood hydrograph in different models showed that SVM model had more efficiency and accuracy than the other two models in predicting rainfall, air temperature, and flood hydrograph.

    • A note on stress rotations due to the 2004 $M_{\rm{w}}$ 9.2 Sumatra–Andaman megathrust earthquake

      SILPA K ANIL EARNEST

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      Here we study the evolution of stress and its rotations in the Sumatra–Andaman Subduction Zone (SASZ) after the 2004 $M_{\rm{w}}$ 9.2 megathrust earthquake, using moment tensor stress inversions. Models indicate returning of North Andaman stress regime to the inter-seismic oblique-compression, after a short stint of extension. Likewise, Little Andamans experience extension indicating a trench-ward guidance of extensional stresses. Similarly, Nicobar regime is presently normal-oblique, from early post-seismic reverse-oblique, and North Sumatra experiences pure-reverse regime. The influence of the Wharton Basin stress field and 2012 earthquakes on the SASZ fore-arc deformation is also probed. A near-complete co-seismic stress-relief is observed at Nicobar, followed by North Sumatra and Little Andaman. Co-seismic and post-seismic model comparisons indicate strong correlation with zones of co-seismic stress relief and regions of rapid post-seismic reloading. The North Andaman shows a northward compressive shear than the margin-normal component of subduction, as evident from prominent oblique stress regime with lower co-seismic stress relief and lack of post-seismic back rotations. At Andaman Spreading Ridge (ASR), transition from oblique to extensional stress indicates lateral shear to back-arc spreading enhancement.

    • Streamflow estimation in ungauged basins using watershed classification and regionalization techniques

      GANVIR KANISHKA ELDHO T I

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      Classifying watersheds prior to regionalization improves streamflow predictions in ungauged basin. Present study aims to assess the ability of combining watershed classification using dimensionality reduction techniques with regionalization methods for reliable streamflow prediction using soil and water assessment tool (SWAT). Isomap and principal component analysis (PCA) are applied to watershed attributes of 30 watersheds from Godavari river basin in India to classify them. The best classification technique is determined by calculating similarity index (SI). The results showed that Isomap is better at classifying hydrologically similar watersheds than PCA with an average SI value of 0.448. The regionalization methods such as global mean, inverse distance weighted (IDW) and physical similarity were applied to transfer the parameters from watersheds of best watershed classification group to the pseudo-ungauged watersheds, using SWAT model. The present study suggests that classifying watersheds with Isomap and regionalization using physical similarity improves the efficiency of streamflow estimation in ungauged basins.

    • Radiative characteristics of near-surface aerosols at a tropical site: An estimation based on concurrent measurements of their physico-chemical characteristics

      ARYASREE S PRABHA R NAIR PRASHANT HEGDE

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      This study is an attempt to estimate the radiative characteristics of aerosols, namely, the scattering coefficient ($\beta_{\rm{sc}}$), absorption coefficient ($\beta_{\rm{ab}}$), extinction coefficient ($\beta_{\rm{ex}}$), single scattering albedo ($\omega$) and the phase function P($\theta$), on a seasonal basis, incorporating the concurrent measurements of aerosol mass loading, size distribution and chemical composition at the tropical coastal site, Thiruvananthapuram. The software package Optical Properties of Aerosols and Clouds (OPAC) has been made use for the estimation of the radiative parameters. This paper presents the seasonal features of aerosol chemical composition and their source characteristics also. Along with this, the association between size-resolved number density of aerosols and their chemical characteristics were also investigated through correlation analysis. The location is significantly influenced by human activities as seen from the dominance of the anthropogenic component which is highest in winter (22%) with comparable values in pre-monsoon and post-monsoon and minimum in monsoon (13%). The sea-salt contribution is found to peak in monsoon ($\sim$40%) and attain a minimum in winter. The source characterization using principal component analysis along with back-trajectory analysis showed the seasonally changing mixed aerosol sources over the region. Accordingly, the radiative properties of aerosols also exhibit significant seasonal variations. $\beta_{\rm{sc}}$ varied from 0.04 to 0.14 km$^{-1}$ and $\beta_{\rm{ab}}$ between 0.01 and 0.05 km$^{-1}$ over a year. The single-scattering albedo exhibited significant seasonal differences being $\sim$0.71 for winter and $\sim$0.89 (0.55 $\mu$m) for monsoon season, indicating the presence of more absorbing aerosols in winter.

    • Correlation of spectral acceleration values in Iranian ground motions

      REZVAN MOADDAB VAHID JAHANGIRI HAMZEH SHAKIB

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      Spectrum compatibility is commonly used as a tool for ground motion record selection in order to perform dynamic analysis. Conditional mean spectrum calculation, which can be used as a target spectrum, requires obtaining correlation coefficients between spectral acceleration values at multiple periods. To date, the correlation coefficients have not been evaluated exclusively from ground motions recorded in Iran. This study represents results obtained from the calculation of correlations for spectral acceleration values from Iranian ground motion data and Zagros and Alborz-central Iran seismic regions, separately. The obtained results can be used for conditional mean spectrum calculations at Iranian sites. The observed correlation coefficients for Iranian records are compared to the correlations developed from the Western United States ground motion data. It is seen that correlation coefficients obtained from the Western United States ground motion data are less than the ones calculated in the study and therefore would cause further reducing of the target spectrum of interest.

    • Zircon U–Pb ages and geochemistry of granitoid from the southwest part of the Taslicay batholith: Implications for Neotethyan closure in Eastern Anatolia, Turkey

      MUSTAFA ACLAN INCI KIBARIYE TURGUT

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      The composite Taslicay batholith that is located in the Eastern Anatolian Accretionary Complex (EAAC) includes I- and S-type granitoid rocks. This batholith occurred as a result of the collision between Arabian and Eurasian plates along the Bitlis–Zagros suture zone during the Early Miocene (Burdigalian). This paper presents new whole rock geochemical and zircon U–Pb geochronological data from the southwest part of Taslicay batholith. The study area contains S-type granitoids such as tonalite, granodiorite, monzogranite, and granite. These rocks are characterized by enrichments in large ion lithophile elements (LILEs) (Cs, Ba, Rb, K) and light rare earth elements (LREEs), and depletions in high field strength elements (HFSEs) (Nb, P, Ti). They contain a number of mafic microgranular enclaves (MMEs) that are quartz microdiorite in composition. Aluminium Saturation Index (ASI) and CIPW normative corundum values of these granitoids vary between 0.98 and 1.22 and 0.06–1.55%, respectively. The zircon U–Pb ages of the studied granitoids range between 19.8 and 20.0 Ma. Considering all geological, geochemical and geochronological data, we suggest that S-type granitoids from the southwest part of Taslicay batholith were formed with assimilation fractional crystallization (AFC) from a hybrid magma source in a syn-collisional (Arabian–Eurasian collision) tectonic environment.

    • Mineral chemistry of high-Al chromian spinel from ultramafic rocks of the Babina–Prithvipur transect, Bundelkhand Craton, central India: Implication for petrogenesis and tectonic setting

      ABINASH SAHU NEERAJ VISHWAKARMA YAMUNA SINGH VERMA C B

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      Bundelkhand Craton is an important Archaean cratonic nuclei of the Central Indian Shield and comprises two greenstone complexes, i.e., the Babina–Mauranipur Greenstone Belt and the Girar–Madawara Greenstone Belt. The E–W trending Babina–Mauranipur Greenstone Belt in the central part of the craton, encloses several isolated lensoid shaped ultramafic bodies which has suffered various degrees of alteration and metamorphism. As per modal mineral analysis, the ultramafic rocks of the Babina–Prithvipur section belong to harzburgite and also contain high-Al chromian spinel along with olivine, ortho-pyroxene and amphibole. Mineral chemistry reveals that the spinels are of high Al and Cr poor variety, where Al$_{2}$O$_{3}$ and Cr$_{2}$O$_{3}$ contents range from 40.06 to 54.34 wt.% and 9.05 to 14.89 wt.%, respectively. The TiO$_{2}$ content is extremely low (average $\approx$0.07 wt.%). The Cr# value of the spinel is < 0.2, whereas Mg# ranges from 0.495 to 0.633. The forsterite contents of the olivine ranges from 86.088 to 88.105 wt.%. Average CaO and NiO contents of the olivine stand 0.03 and 0.24 wt.%, respectively. Composition of the analyzed ortho-pyroxene belongs to En$_{84.20–87.75}$Wo$_{0.15–0.39}$ with low CaO content of 0.080 to 0.207 wt.%. As per mineral chemistry, these harzburgite rocks of the Babina–Prithvipur section belong to mantle peridotite. Melt calculation for the spinel also suggests a least differentiated magmatic product, which is also supported by the olivine spinel mantle array diagram as all the samples are plotted within the mantle array field very close to the fertile mantle source. Low TiO$_{2}$ and high Al contents of spinel also reflect the MORB type peridotite characteristics for these ultramafic rocks which probably originated from least differentiated plagioclase free mantle derived harzburgite/lherzolitic magma in a rift related spreading centre. As a whole these ultramafic rocks appear to be the remnant of the early crust that existed during the Archaean time.

    • Estimation of sediment load for Himalayan Rivers: Case study of Kaligandaki in Nepal

      PENNAN CHINNASAMY ADITYA SOOD

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      Himalayan regions have increasing sediment yield due to undulating topography, slope and improper watershed management. However, due to limited observation data, and site accessibility issues, less studies have quantified sedimentation loads in the Himalayas, especially Nepal. This has hindered the investments on run-of-river hydropower projects as high and unpredicted sedimentation has increased losses in hydropower production. Therefore, there is a need to understand key physical processes driving sedimentation in these regions, with the available data. This study used the Soil and Water Assessment Tool (SWAT) to estimate the sedimentation yields in the Kaligandaki basin of Nepal, which is an important tributary that drains into the Ganges. Multi-source data from field observations, remote sensing platforms, surveys and government records were used to set up and run the SWAT model for the Kaligandaki basin from 2000 to 2009. Results for the 10-year model run indicate that 73% of the total sediment load is estimated to come from the upstream regions (also known as High Himalayan region), while only 27% is contributed from the Middle and High Mountain regions (where land management-based interventions were deemed most feasible for future scenarios). The average sediment concentration was 1986 mg/kg (ppm), with values of 8432 and 12 mg/kg (ppm) for maximum and minimum, respectively. Such high sedimentation rates can impact river ecosystems (due to siltation), ecosystem services and hydropower generation. In addition, model results indicate the need for better high frequency observation data. Results from this study can aid in better watershed management, which is aimed at reducing sedimentation load and protecting Himalayan rivers.

    • Thinking about water and air to attain Sustainable Development Goals during times of COVID-19 Pandemic

      ABHIJIT MUKHERJEE SURESH BABU S SUBIMAL GHOSH

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      In 2020, we are in the doorstep of a new decade, during which the UN Sustainable Development Goals (SDG) are to be achieved, collectively as one nation and one human-hood, where availability of safe, sustainable and clean water and air forms the core of multiple goals. However, the emergence of the COVID-19 pandemic across the globe has resulted a newer challenge and paradigm for an evolving socio-scientific priorities. It is generally expected that the impacts of the pandemic would be in shorter time-scale, while the planned time and pathway for attaining the SDG are typically mandated in longer-term, hence may remain mostly unaffected. However, the stringent lockdown measures, isolated economies and financial burden to contain the pandemic emergency have resulted to slowdown of socio-economic development, which if continues for a longer period, would put a question mark on developing plans and pathways to achieve the SDGs, even in decadal-scale. Hence, in these newer times, it is important to understand the real priorities of availability of clean water and air, which are already stressed worldwide and in India, because of various natural and human-influenced triggers. This ongoing pandemic has provided an unprecedented opportunity to evaluate the impact of human development and consequent feedback of nature and human society in pre- and post-COVID scenarios on water–air–human life, which can help to re-think and re-orient the societal development priorities. It is a rare opportunity for scientists to impress the policy-makers with real-time examples on the efficacies of potential mitigation strategies for climate change, water and air pollution, and the importance of enduring investment on environmental causes and consequent benefits that can secure health and development for our future generations.

      $\bf{Highlights}$

      $\bullet$ Environmental pollution and climate change pose a high risk for human survival.

      $\bullet$ Develop resilience to attain SDGs in spite of economic constraints caused by COVID-19.

      $\bullet$ Set real priorities of availability of clean water and air for future, in a unified world.

    • Petrography and whole-rock geochemistry of Oligocene Barail Sandstones of Surma basin: Implications for tectono-provenance and paleoclimatic condition

      PRADIP BORGOHAIN FARUQUE HUSSAIN M DEVOJIT BEZBARUAH VANTHANGLIANA V PARAKH PROTIM PHUKAN MANASH PRATIM GOGOI BUBUL BHARALI

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      The Oligocene Barail Sandstones of Surma basin from parts of Champhai District of Mizoram, northeast India has been studied for their tectono-provenance setting using petrography and geochemistry. The studied sandstones are poor to moderately sorted, subarkosic to sub-litharenite and show dominance of quartz (avg. 54.46%) followed by feldspars (avg. 7.22%), rock fragments (avg. 4.98%), mica (avg. 5.89%), matrix (avg. 14.47%) and cement (avg. 12.98%). Dominance of polycrystalline and undulatory monocrystalline quartz indicates contribution from medium grade metamorphic sources, primarily of granite gneisses. High concentration of SiO$_{2}$ with moderate to low concentration of Al$_{2}$O$_{3}$, Fe$_{2}$O$_{3}$, MgO, Na$_{2}$O and K$_{2}$O resembles the composition of upper continental crust. Moreover, moderate to high concentration of Th and V, depleted value of Ni along with TiO$_{2}$/Zr suggests derivation of sediments from felsic sources. The ratios of Eu/Eu* (avg. 0.63) and La$_{\rm {N}}$/Lu$_{\rm{N}}$ bears resemblance with the upper continental crust. Overall analyses show that the sediments were derived from the felsic terrain of neighbouring orogens probably represented by granite-gneisses and have undergone a moderate degree of weathering (avg. values of CIA: 70.20, CIW: 81.03, PIA: 77.63, WIP: 38.45, ICV: 1.06, I$_{\rm{w}}$ = 2) in a semi-humid to humid climatic conditions [Q$_{\rm{p}}$ /(F + RF):Q$_{\rm{t}}$ /(F + RF) = 0.20].

    • An efficient global optimization method for self-potential data inversion using micro-differential evolution

      SUNGKONO

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      Self-potential (SP) method has many applications, where the interpretation of SP data can be used for qualitative and quantitative interpretation. However, inversion of SP data in this paper is of quantitative interpretation and consists of highly non-linear, multimodal data and deploys global optimum method (GOM). Micro-differential evolution (MDE) is a GOM with small or micro-population size (5–8 populations) for each iteration. Consequently, this approach involves small numbers of forward computation in the inversion process. Two MDE variants, including adaptive MDE ($\mu$JADE) and vectorized random mutation factor (MVDE) were tested first for different level of noises containing synthetic SP data with single anomaly and applied to synthetic SP data of multiple anomalies. The MDE variants are reliable and effective for inverting noisy SP data. Furthermore, in order to check the rationality of MDE variants, the algorithm is applied to seven field data from different applications, including groundwater exploration, shear zone tracing, water accumulation in landslides and embankment stability assessment. The model parameters revealed by MDE variants are accurate and show good agreement with the previous results estimated using other approaches. In addition, MDE variants also require fewer forward modelling calculations than other optimization approaches.

    • Paleoenvironment shifts during MIS 3: Loess and loess paleosols of Kashmir Valley, India

      ASIF ALI HEMA ACHYUTHAN

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      Kashmir valley receives the rainfall owing to the dominant westerly winds and experiences less impact of the southwest monsoonal rains (SWM). In this valley, loess and loess paleosols occur as a thin veneer covering the landscape. The loess paleosols form an important proxy for paleoclimate reconstruction and understanding the late Quaternary paleoenvironmental shifts. For this purpose, the loess, paleosols within the loess lithosections were lithologged and the sediment samples were subjected to various grain-size textural and geochemical analysis. The U-ratio of the sediments supported by parameters such as TOC, CaCO$_{3}$ content, ratios of Zr/Rb, Rb/Sr, Ba/Sr, K/Ba, K/Rb, chemical index of alteration (CIA) and clay mineralogy indicate that the loess paleosols have undergone weak to moderate degree of pedogenesis. The U-ratio and Zr/Sr ratio also reflect variations in the wind velocity ranging from weak to moderate conditions for the loess deposition. The Ba/Sr and Rb/Sr ratios signify varied precipitation conditions, particularly with higher precipitation during the paleosol formation. The A–CN–K plot exhibits weaker to intermediate type of weathering of the loess horizons. TiO$_{2}$% vs. Al$_{2}$O$_{3}$% binary plot illustarates mostly basaltic to rhyolite/granite type of rock source and the Panjal Traps is one of the major sources of the loess deposition. The lower end of the exposed Choori and Burzahama lithosections were dated by OSL method to 54 $\pm$ 2 ka at 9.5 m depth and 52 $\pm$  2 ka at 8 m of depth, respectively. Geochemical analysis and OSL dating of the Choori and Burzahama lithosections reveal that climate during the marine isotope stage 3 (MIS 3) was dominantly warm and dry (stadial conditions) in Kashmir valley when the loess layers covered the valley and since then the loess horizons have undergone weak to intermediate, moderate type of weathering in cool and dry conditions.

    • Assessment of regional best-fit probability density function of annual maximum rainfall using CFSR precipitation data

      NKPA M OGAREKPE IMOKHAI T TENEBE PRAISEGOD C EMENIKE OBIANUJU A UDODI RICHARD E ANTIGHA

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      The upper Cross River basin (UCRB) fits a true description of a data scarce watershed in respect of climatic data. This paper seeks to determine the best-fit probability density function (PDF) of annual maximum rainfall for the UCRB using the Climate Forecast System Reanalysis (CFSR) precipitation data. Also, to evaluate the performance of the Intergovernmental Panel on Climate Change (IPCC) Coupled Model Inter-comparison Project (CMIP3) Fourth Assessment Report (AR4) Global Circulation Models (GCMs) in simulating the monthly precipitation in the UCRB considering 1979–2014 data. For the determination of the best-fit PDF, the models under review included the generalized extreme value (GEV), normal, gamma, Weibull and log-normal (LN) distributions. Twenty-four weather station datasets were obtained and subjected to frequency distribution analysis on per station basis, and subsequently fitted to the respective PDFs. Also, simulated monthly precipitation data obtained from 16 AR4 GCMs, for weather station p6191, were subjected to frequency distribution analysis. The results showed the percentages of best-fit to worst-fit PDFs, considering the total number of stations, as follows: 54.17%, 45.83%, 37.50%, 45.83%, and 50%/50%. These percentages corresponded to GEV, Weibull, gamma, gamma, and LN/normal, respectively. The comparison of the predicted and observed values using the Chi-square goodness-of-fit test revealed that the GEV PDF is the best-fit model for the UCRB. The correlation coefficient values further corroborated the correctness of the test. The PDF of the observed data (weather station p6191) and the simulations of the 16 GCMs computed using monthly rainfall datasets were compared using a mean square error (MSE) dependent skill score. The result from this study suggested that the CGCM3.1 (T47) and MRI-CGCM2.3.2 provide the best representations of precipitation, considering about 36 years trend for station p6191. The results have no influence on how well the models perform in other geographical locations.

    • Extending the limit of widespread dispersed Toba volcanic glass shards and identification of new in-situ volcanic events in the Central Indian Ocean Basin

      ANKEETA AMONKAR SRIDHAR D IYER BABU E V S S K MANJU S

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      We report the widespread extent of Toba volcanic glass shards in the Central Indian Ocean Basin. Investigation of four sediment cores (7$^{\circ}$–17$^{\circ}$S) revealed several shard-rich horizons (SRH) that provide the first detailed tephrochronology for volcanic glass shards in the CIOB. A comparative study of surface sediments floored with Youngest Toba Tuff (YTT), indicate that irrespective of the rate of sedimentation, YTT in the basin is restricted to a depth of <35 cm-bsf. We utilized microtektites (0.77 Ma), associated with the Oldest Toba Tuff (OTT) glass shards, as a proxy for age calculation of the SRH. The results are comparable with well-established ages derived from paleomagnetic and $\delta^{18}$O methods for the Leg 21 ODP Site 758. The other significant finding of this study includes the first report of Middle Toba Tuff (equivalent to Layer C) and Layer D that are present between YTT and OTT (Layer E) and also Layers G, H, h, I, J, K, L and M. All these layers correspond with those reported for ODP Site 758. Furthermore, two SRH between layers G and H show signatures of localized in-situ phreatomagmatic origin, suggesting that CIOB is apparently more active – tectonically and volcanically than it is presumed.

    • Model showing influence of tectonics and energy condition of the fluvial environment on facies architecture: A case history of Quaternary alluvial deposits of Purna basin, central India

      ASHOK K SRIVASTAVA MANGLA N BANSOD AJAB SINGH VIVEK M KALE

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      Present work includes identification of lithofacies and reconstruction of depositional environments including controls of tectonics, and energy condition of the medium on sedimentation pattern of alluvial deposits of Purna basin, central India. The basin exhibits good development of dominantly areno-argillaceous sediments along with restricted occurrences of boulder-pebbly lithounits, covering together an area of 6,522 km$^{2}$. These sediments are also characterized by preservation of various calcrete morphotypes, vertebrate remains and Youngest Toba Tuff (YTT) ash in certain stratigraphic units. The work is based on detailed field and lithological studies of 20 river-cut sections exposed along the course of Purna river, representing entire alluvial deposits in both vertical and lateral profiles. Three lithofacies associations have been identified, i.e., (1) gravelly facies association (FA-1), (2) sandy facies association (FA-2) and, (3) silty-clayey facies association (FA-3). These associations consist of total 10 lithofacies distributed as: (i) matrix supported massive gravelly (Gmm) facies, (ii) matrix supported gravelly (Gmg) facies, (iii) horizontally stratified gravelly (Gh) facies, (iv) planar stratified gravelly (Gp) facies (FA-1), (v) horizontal sandy (Sh) facies, (vi) planar cross stratified sandy (Sp) facies, (vii) low angle cross bedded sandy (Sl) facies, (viii) massive sandy (Sm) facies (FA-2), (ix) laminated sandy (Fl) facies, and (x) palaeosol (P) facies (FA-3). Various architectural elements have also been identified. Based on lateral and vertical profiling of the lithofacies architecture, it is interpreted that gravel dominated facies in the mountainous region of the basin area are deposited by medium to high energy debris flow,whereas sandy and silty-clayey facies in the plain area are because of saltation and suspension modes of deposition under medium to low energy condition of depositing medium. The tectonic and topographical controls are well reflected on the sedimentation pattern and the same has been illustrated by proposing a model. Discussions along with the model have also been made on the progressive development of bazada or, pediment zone along the northern margin of the basin marked by the foothills of Satpura mountain ranges.

    • Characteristics of rock–water interaction in Gangotri proglacier meltwater streams at higher altitude catchment Garhwal Himalaya, Uttarakhand, India

      SARFARAZ AHMAD ZABIULLAH ANSARI

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      Proglacial streams play an important role in water–rock interaction due to different climatic conditions at different altitudes. The main objective of the present study is to analyze the variation of glacier hydrochemistry and sedimentation processes at different altitudes. The results show that the bed sediments in higher altitude streams are fine sand, poorly sorted, leptokurtic in nature and dominated with high proportion of feldspar and biotite. At lower altitude, the bed sediment is coarse sand, moderately sorted and platykurtic in nature with relatively high proportion of quartz. The high concentration of biotite and feldspar in silt/lay size fraction are responsible for high proportion of magnesium in Gangotri proglacier meltwater than others. Meltwater is slightly acidic and hydrochemical facies shows Ca$^{+2}$–Mg$^{+2}$–HCO$_3^{-}$ type. The concentration of Ca$^{+2}$, Mg$^{+2}$, Na$^{+}$, and K$^{+}$ decreases with altitude due to dilution produced by augmentation of freshly monsoonal recharged groundwater from meadow and forest in downstream. The cation exchange, carbonate/silicate weathering and groundwater, subglacial water sources control the hydrochemistry of proglacial streams at lower altitude.

    • Evaluation of seismic hazard with probabilistic approach for Antakya Province (Turkey)

      TALAS FIKRET KURNAZ YIGIT INCE

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      Antakya province is tectonically affected by Dead Sea and East Anatolian faults and the Cyprus arc. Although there had been major and devastating earthquakes in the historical period, the fact that there is no major earthquake in the instrumental period increases the risk of seismic hazard of the region. In this study, it is aimed to perform a probabilistic seismic hazard analysis application for Antakya province, Turkey. For this purpose, the earthquakes (M$_w$$\geq$ 4) which occurred between 1900 and 2017 were used. Nine seismic source zones that could affect the Antakya province were identified and the seismic hazard parameters calculated for each zone. Peak ground acceleration (PGA) values that can occur in a possible earthquake were obtained according to a recurrence period of 475 yrs by using two different attenuation relationships and presented with iso-acceleration maps. The calculated PGA values in the study area are found as between 0.32 and 0.57 g for both attenuation relationships. The areas located on the north of Kirikhan district have the highest risk of seismic hazard in the study area according to determined PGA values.

    • Influence of trapped soft/stiff soil layer in seismic site response analysis

      NARAYAN ROY SIBAPRIYA MUKHERJEE RAMENDU BIKAS SAHU

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      As the ground response analysis serves an integral part of site specific seismic hazard study to obtain design ground motion, a proper and accurate estimation should be of prime importance. The paper presents a study on the effect of trapped soft and stiff soil layer on equivalent linear ground response analysis implemented in computer program STRATA. For this purpose, the concept of normally stiff and inversely stiff soil profiles have been introduced. The study clearly indicates the higher impact of a trapped soft soil layer profile, i.e., inversely stiff soil profile with soft layer, in comparison with trapped stiff layer profile, i.e., inversely stiff profile with stiff layer. For low to moderate ground motions, as the depth of the trapped soft layer increases, peak amplification and peak frequency reduces, and for high intensity input ground motion, significant reduction only in the peak frequencies is observed. On the other hand, as the depth of trapped stiff soil layer increases the outcome of ground response analysis remain quite similar. Peak transfer function, peak frequency, peak spectral ratio and peak spectral acceleration are found to exhibit a COV $\leq$ 60 to 100% for all combinations of IS-Soft profiles, whereas, IS-Stiff profiles exhibit a maximum COV $\leq$ 15 to 25% for all the considered input ground motions. Computed normalized-root mean square error (Norm-RMSE) values also clearly indicate the higher deviations in the ground response analysis for different combinations of trapped soft soil profiles, from that of normally stiff profile, whereas, trapped stiff layer profiles show lower deviations in the Norm-RMSE values. The profiles with trapped soft layer exhibit a Norm-RMSE value  $\leq$ 0.8, whereas, trapped stiff layer profiles exhibit a Norm-RMSE value  $\leq$ 0.2, which clearly demonstrate the large deviations in the outcome of ground response analysis in case of trapped soft layer profiles.

    • Correction to: Evaluation of the convective mass flux profiles associated with cumulus parameterization schemes of CMIP5 models

      PARTHASARATHI MUKHOPADHYAY KUMAR ROY

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    • Impact of electrified and non-electrified clouds on the inter-seasonal characteristics of surface-based precipitation

      KAUSTAV CHAKRAVARTY MURUGAVEL P ANGEL A CHRISTY SINGH V PANDITHURAI G

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      A multi-sensor analysis of the characteristics of electrified and non-electrified clouds along with their impact on the surface-based raindrop size distribution (DSD) during the inter-seasonal phases of Indian summer monsoon over a heavy precipitation region of Western Ghat (WG) has been highlighted in the present paper. The analysis reveals that during the pre-monsoon (monsoon) months, raindrops of larger diameter dominate the rainfall evolving from the non-electrified (electrified) clouds compared to the rainfall evolving from the electrified (non-electrified) ones. The complex relationship of the convective rainfall with highly charged electrified clouds forces the smaller drops aloft and thereby allowing the larger drops to precipitate locally during the pre-monsoon season. While for the monsoon months, as most of the rainfall originates from the deep clouds, the chances of drops to break-up/evaporate is comparatively less for the precipitation evolving from electrified clouds with charged droplets with respect to the non-electrified ones. Hence, drops of larger diameter dominate the monsoon rainfall associated with lightning. Correspondingly, the paper also highlighted a case study of the changing morphology of the vertical structure of clouds and surface precipitation with the evolution of lightning during various stages of a typical rainfall event over the orographic region of WG.

    • Evaluation of convective parameterization schemes in simulation of tropical cyclones by Climate Forecast System model: Version 2

      RADHIKA D KANASE MEDHA S DESHPANDE KRISHNA R P M PARTHASARATHI MUKHOPADHYAY

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      Recently, a high resolution atmospheric general circulation model, i.e., Global Forecast System has been operationalized for 10 days weather forecast over Indian region. However, for extreme weather systems such as cyclones, different physical processes and their interactions with atmosphere and ocean play an important role in cyclone intensity, track, etc. Keeping this in view, Coupled Forecast System model version 2 has been used to evaluate the simulation for three severe cyclones (Phailin, Viyaru and Lehar) of 2013. In the present study, along with already existing mass-flux cumulus parameterization, i.e., Simplified Arakawa–Schubert (SAS) and revised SAS (RSAS) parameterization schemes, an additional convective adjustment scheme, i.e., Betts–Miller–Janjic (BMJ) is implemented and its performance is evaluated for the Indian Ocean cyclones. The experiments are conducted with three cumulus schemes at three different resolutions (T126, T382, and T574). Both SAS and RSAS overestimate convective rain, whereas BMJ scheme produces convective rain comparable with the observation due to the fact that BMJ produces deeper convection and does not trigger the convection too often. BMJ sustains the instability and deep convection longer thereby impacting the cyclone intensity and heavy rainfall associated with it. It is also noted that BMJ is efficient in producing rain than the SAS and RSAS. From the analyses of OLR and rain rate, BMJ is found to simulate a much realistic relation of cloud and precipitation. The paper argues that compared to available SAS and RSAS, BMJ scheme realistically produces heavy precipitation associated with the tropical cyclone over Indian region in a coupled model.

    • Landslide susceptibility mapping using bivariate statistical method for the hilly township of Mussoorie and its surrounding areas, Uttarakhand Himalaya

      PRATAP RAM VIKRAM GUPTA MEENAKSHI DEVI NEERAJ VISHWAKARMA

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      Landslide is a normal geomorphic process that becomes hazardous when interfering with any development activity. It has been noted that ${\sim}$400 causalities occur in the Himalayan region every year due to this phenomenon. The frequency and magnitude of the landslides increase every year, particularly in the hilly townships. This demands the large scale landslide susceptibility, hazard, risk, and vulnerability assessment of the region to be carried out. In the present study, Mussoorie Township and its surrounding areas located in the Lesser Himalaya has been chosen for Landslide Susceptibility Mapping (LSM) that involved bivariate statistical Yule coefficient (YC) method. It calculates the binary association between landslides and its various possible causative factors like lithology, land use-landcover (LULC), slope, aspect, curvature, elevation, road-cut, drainage, and lineament. The results indicate that ${\sim}$44% of the study area falls under very high, high and moderate landslide susceptible zones and ${\sim}$56% in the low and very low landslide susceptible zones. The dominant part of the area falling under high and moderate landslide susceptible zones lies in the area covered by highly fractured Krol limestone exhibiting slope ranging between 65$^{\circ}$ and 77$^{\circ}$. The study would be useful to the planners for the land-use planning of the area.

    • Abrupt changes in mean temperature over India during 1901–2010

      BHATLA R SHRUTI VERMA SOUMIK GHOSH ANKITA GUPTA

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      Since eternity, the Earth’s temperature has varied or fluctuated; it has its cooling and hot timing dependency on its orbital position as well as the isolation received from the Sun. The global climate continues to change rapidly compared to the speed of the natural variations in climate. Therefore, the spatially complete representations of surface climate are required for many purposes in applied sciences. But in recent centuries, the main matter of concern is that Earth’s normal temperature fluctuation is being influenced by some external factors such as enhanced greenhouse gases because of extreme uses of fossil fuels, severe industrialization, advance urbanization, etc. This study presents a comprehensive surface temperature dataset of Climatic Research Unit (CRU) available since 1901 for India, which is used to document significant changes in Indian temperature over ten decades, during winter season (January and February), pre-monsoon (March–May), monsoon (June–September) and post-monsoon (October–December) to examine the patterns and possible effects of global warming. A strong increasing pattern is observed with the fast growing of the development after 1950 which has shown nearly doubled in the last 50 yrs. The mean temperature during winter for the 2000s shows a consistent pattern of warming over the Himalayan region, northwestern and southern India, and a pattern of the warming observed over northeastern India and extending southwestward across central India during post-monsoon.

    • Rare earth element resources: Indian context

      CHALAPATHI RAO N V

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    • Impact of rainfall intensity, monsoon and MJO to rainfall merging in the Indonesian maritime continent

      GIARNO MUHAMMAD PRAMONO HADI SLAMET SUPRAYOGI SIGIT HERUMURTI

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      Merging is an estimation technique used to improve the accuracy of rainfall predictions by combining two rainfall predictions. In fact, the performance of remote sensing estimates varies in each place and time where the influence of the time has a relationship with the global weather phenomenon. The aim of this study is to investigate the influence of the two most influential phenomena on rainfall in the Indonesian maritime continent: the monsoon and Madden–Julian Oscillation. This assessment also analyzed the impact of rainfall intensity. While the change in correlation, root-mean-square-error (RMSE) and mean-absolute-error (MAE) will be used to assess the effectiveness of merging of monsoons and MJO. The result shows that the intensity of rainfall apparently affect the accuracy of merging, where the moderate-intensity has low RMSE and MAE and high correlation compared to heavy or very heavy rainfall. While comparing other phases and season found, the 5th phase of MJO and rainy seasons have the best performance. Moreover, among modification methods, the modification of conditional merging (CM) is the best merging technique for all seasons and MJO’s phases.

    • Application of hind cast in identifying extreme events over India

      JOHNY C J PRASAD V S

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      India Meteorological Department (IMD) is operationally producing forecasts at T1534 resolution using NCMRWF GFS (NGFS) model and biases are reported in some regions. In order to identify the model biases and applying necessary correction measures to improve forecast, retrospective forecast is carried out for the 20 yrs period from 1999–2018 using operational version of NGFS model. In this study, model’s ability to predict extreme temperature and rainfall events in Indian region irrespective of model biases is investigated. It is found that model is able to predict extreme temperature events accurately with sufficiently long lead time (7 days). In case of extreme rainfall at shorter lead time (3 days), model is able to predict accurately and accuracy decreases with increase in lead time. Employing bias correction methods reduced large biases in some regions.

    • Assessment and evaluation of groundwater vulnerability index maps of Upper Palar River Basin, Tamilnadu, India

      SUBBARAYAN SARAVANAN PITCHAIKANI S VENKATESAN G

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      The present study focuses on the assessment of groundwater vulnerability in the Upper Palar river basin, Tamil Nadu, India using the DRASTIC method, which consists of seven parameters obtained from various sources and created as map layers. To determine the groundwater vulnerable zones, the net recharge parameter considered in the DRASTIC model is estimated by four different methods, viz., SCS-CN, Piscopo, Chaturvedi, and groundwater fluctuation recharge methods and the results were compared. The vulnerability maps were generated by four recharge estimation methods, such as water table fluctuation method, Piscopo, SCS-CN and empirical formulae of Chaturvedi methods. This vulnerability class were validated with the observed groundwater quality (nitrate concentration) measured from 30 wells in the study area. The results were classified into four categories such as low, moderate, high, and very high. From the results obtained using DRASTIC with the Chaturvedi method, very high vulnerability is observed in the southern regions and low vulnerability in the north and southwest regions. Using the Piscopo method, the very high vulnerability is distributed along the lower half of the river and southeast side, and the low vulnerability covers the north part of the river basin. Similarly using the SCS-CN method, the very high vulnerability is seen along the river basin and low vulnerability along the central-north and south regions. Using the groundwater fluctuation method, very high vulnerability falls under the small part of the southeast side, but low vulnerability covers the south-west and east sides of the river basin. The different methods adopted to estimate the recharge rate in the study revealed the dependency level of the vulnerability on that parameter. Also, the study area characteristic is best observed by the results of these four methods. All the four methods gave very good results and better knowledge about each factor and a better understanding of the groundwater susceptible zones to pollution in the study area. Among the four methods, Piscopo and WTF methods were found to be best applicable for the selected study area.

    • Meteorological trends over Satluj River Basin in Indian Himalaya under climate change scenarios

      GUPTA A DIMRI A P THAYYEN R SANJAY JAIN SARAD JAIN

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      Temperature and precipitation distributions depend on variable topography and heterogeneous landuse/landcover in the Indian Himalayan Region (IHR). It imparts a major concern for hydrological, glaciological modelling, dam structure assessment, etc. Thus, there is an inherent requirement of robust information for climate impact studies over the topographical variable and landuse heterogenous region in the Indian Himalayan Region (IHR). In particular, the importance of bias corrections become critically important over Himalayan river basins, in which model outputs with the corresponding in-situ observations are used for improving the model distribution. These improved details in present and future, as well, are important to carry out the climate change impact studies at basin scale for hydrological, glaciological, climatological studies, etc. Thus, in the present study firstly, model fields are bias corrected with the corresponding in-situ observations. And then trends in these bias corrected data is compared with the corresponding in-situ observations. These assessment of present and future changes in temperature and precipitation over Satluj River Basin (SRB) located in the western Himalayas is illustrated. Model fields are considered from a Regional climate model (REMO) from Coordinated Regional Downscaling Experiment-South Asia (CORDEX-SA) in three Representative Concentration Pathways (RCPs), i.e., 2.6, 4.5 and 8.5 W/m$^{2}$. These projections are bias corrected using distributed quantile mapping. The precipitation (temperature) bias correction is performed using the distributed quantile mapping on the gamma (normal) distribution. The standard trend statistics is applied for quantitative assessment. A good capture of bias correction in temperature and precipitation is illustrated. Efficient bias removal is depicted in cumulative distribution curve (CDF) at individual station. Trend analysis shows that highest rate of precipitation decrement at low altitude station (Kasol) with the rate of $−$6.362 mm/year in RCP 8.5. Over the SRB highest rate of temperature increment is seen at highest altitude station (Kaza) with the rate of 0.084$^{\circ}$C/year in RCP 8.5. On an average, fall in precipitation and increase in temperature with >99% confidence level in RCP 8.5 is seen. In addition, intensity lowers in other lower RCPs. The study sums up with the efficacy of CORDEX-SA REMO model in capturing present and future change in temperature and precipitation over the SRB in western Himalayas using the bias correction.

    • Mapping groundwater potential zones using remote sensing and geographical information systems in a fractured rock setting, Southern Flinders Ranges, South Australia

      STEPHEN G FILDES IAN F CLARK NARA M SOMARATNE GLYN ASHMAN

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      In Australia, water resource management is a major socio-economic and environmental issue and an essential component of progress. This is more acute in arid and semi-arid regions of Australia. The Southern Flinders Ranges townships of Quorn and Hawker in common with much of the Flinders Ranges suffers from a lack of reliable data to help water resource managers. This paper discusses the delineation and assessment of groundwater potential zones using remote sensing and geospatial techniques in the region, using multi-criteria analyses. The study integrates many thematic layers (rainfall, lithology, lineament density, topographic wetness, slope and aspect) in a GIS environment in order to identify groundwater potential zones. Weights are assigned to class attributes within and between each thematic data layer using an Analytical Hierarchy Process based on the relative importance of each layer. The weighted thematic data layers are then combined to produce a probability of groundwater potential zone map of each study area. The groundwater potential zones were verified with available water data, and showed consistency with the interpretations.

    • Post-breakup deformations in the Bay of Bengal: Response of crustal strata to the sediment load

      KRISHNA K S ISMAIEL M SRINIVAS K SAHA D

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      Passive continental margins are tectonically inactive, but a few of them including the East India Passive Margin (EIPM) show evidences for post-breakup deformations. This unusual process prompted us to investigate the post-rift deformations on EIPM and adjacent deep-water region for understanding the possible mechanisms. Seismic reflection images of the Bay of Bengal reveal a post-rift deformation with a manifestation of extensional faults in Krishna–Godavari (K–G) basin and on flanks of the 85$^{\circ}$E Ridge. In K–G basin, one of the rift-related faults reactivated during the Early Miocene time ($\sim$16 Ma), while on flanks of the 85$^{\circ}$E Ridge new normal faults originated at about 6.8 Ma. From detailed analysis of fault throws, it is observed that the fault in K–G basin recorded a cumulative throw of about 900 m between the basement and Early Miocene horizon ($\sim$16 Ma), later the fault was reactivated at 6.8 Ma and continued the activity progressively until 0.3 Ma before cessation. The fault system on the margin spatially extends for about 300 km between offshore extensions of the Pranahita–Godavari graben and Nagavali–Vamshadhara shear zone. The faults on 85$^{\circ}$E Ridge, initiated at 6.8 Ma and continued until 0.8 Ma, have cumulative throws of about 60 and 110 m on western and eastern flanks of the ridge, respectively. Back-stripping analysis of the fault from the K–G basin discloses two distinct phases of subsidence history: (i) during the first phase (120–23 Ma) the basement subsided at a rate of 46–18 m/Myr due to thermal cooling of the lithosphere, (ii) during the second phase (23 Ma–Present) rapid subsidence rate (69.56 m/Myr) of basement is noticed as a consequence of deposition of copious amounts of Bengal Fan sediments. The thick sedimentary strata exerted vertical load on underlying heterogeneous crust that led to build excessive internal stress and release through weak zones (lying at intersecting planes of heterogeneous crustal blocks). The stress, thus released through fault planes has caused the deformation of crust as well as overlying sedimentary strata.

    • Exploring sub-basalt reservoirs using object-oriented imaging: A case study from Kutch–Saurashtra area, India

      DEBASHIS CHATTERJEE PRIYA RANJAN MOHANTY SUNIL SINGH

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      The hydrocarbon strike has been reported above and below basalt (Mesozoic sequences) in shallow water of Kutch–Saurashtra basin of Indian west coast. The evaluation of entrapment conditions within Mesozoic (below basalt) is extremely problematic because of poor quality images, of available data which are not amenable for subsurface mapping. The precise sub-basalt imaging in Kutch–Saurashtra basin is crucial for successful exploration activities in Mesozoic. The challenges for imaging the streamer data are two folds: first, poor data quality, due to poor signal penetration through basalt section and second, masking of signals with multiples and converted waves (PSPP and PSSP). Modelling using Norsar software, reveals that PSSP waves (noise), generate from an offset of about 3000 m from basalt top. We followed a new imaging strategy for achieving good sub-basalt images by proper multiple attenuation, elimination of converted waves, and adequate noise cleaning in different domains with correct estimation of velocity and signal boosting, below basalt. The new images clearly exhibit the sub-basalt horizons like Base of Basalt, Bhuj Formation and Mundra Formation, etc., which are amenable for mapping and pre-stack inversion, a powerful tool for reservoir characterization. The acoustic impedance of gas pay, drastically drops to 8000 unit from background value or 14000 units, delineated lateral extension of pay sand in present study. The new imaging exhibits presence of Graben, half Graben and anticlinal structures formed during Mesozoic and some reverse faults which are key components to unravel the basin tectonics and to aid derive Mesozoic petroleum system.

    • Geomicrobial dynamics of Trans-Himalayan sulfur–borax spring system reveals mesophilic bacteria’s resilience to high heat

      CHAYAN ROY NIBENDU MONDAL ADITYA PEKETI SVETLANA FERNANDES TARUNENDU MAPDER SAMIDA PRABHAKAR VOLVOIKAR PRABIR KUMAR HALDAR NILANJANA NANDI TANNISHA BHATTACHARYA ANINDA MAZUMDAR RANADHIR CHAKRABORTY WRIDDHIMAN GHOSH

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      Geomicrobiology of sulfur–boron-dominated, neutral-pH hydrothermal systems was revealed in a Trans-Himalayan spring named Lotus Pond, located at 4436 m, in Puga Valley, Ladakh (India), where water boils at 85$^{\circ}$C. Water sampled along Lotus Pond’s outflow (vent to an adjacent river called Rulang), representing an 85–14$^{\circ}$C gradient, had high microbial diversity and boron/chloride/sodium/sulfate/thiosulfate concentration; potassium/silicon/sulfide/sulfite was moderately abundant, whereas cesium/lithium small but definite. Majority of the bacterial genera identified in the 85–72$^{\circ}$C samples have no laboratory-growth reported at >45$^{\circ}$C, and some of those mesophiles were culturable. Sulfur-species concentration and isotope-ratio along the hydrothermal gradient, together with the distribution of genera having sulfur-oxidizing members, indicated chemolithotrophic activities in the 85–72$^{\circ}$C sites. While biodiversity increased in the vent-to-river trajectory all-day, maximum rise was invariably between the vent (85–81$^{\circ}$C) and the 78–72$^{\circ}$C site; below 72$^{\circ}$C, diversity increased gradually. Biodiversity of the vent-water exhibited diurnal fluxes relatable to the sub-surface-processes-driven temporal fluxes in physicochemical properties of the discharge. Snow-melts infiltrating (via tectonic faults) the $\sim$160$^{\circ}$C geothermal reservoir located within the breccia, at $\sim$450 m depth, apparently transport mesophilic microbes into the thermal waters. As these micro-organisms emanate with the vent-water, some remain alive, illustrating that natural bacterial populations are more heat-resilient than their laboratory counterparts.

    • Sedimentary thickness of the northern Indo-Gangetic plain inferred from magnetotelluric studies

      DHAMODHARAN S GAUTAM RAWAT SACHIN KUMAR BAGRI D S

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      Knowledge of the sedimentary thickness and configuration of the basement structure are important to estimate the seismic hazards in active foreland basin. We present sedimentary thickness of the northern Indo-Gangetic plain estimated from impedance tensors of 12 magnetotelluric sites. Occam’s one dimensional inversion scheme was applied to invariant of the magnetotelluric tensors for the period range of 0.001–1 sec at each site. Inverted one dimensional model corroborates north-easterly dipping Indian basement and accordingly increased thickness of the sedimentary column towards north and east direction. The top sedimentary layers of varying thickness and resistivity are correlated with the known borewell logs and previous geophysical studies around the study area. Significant difference is observed in the resistivity of the Indian basement and thickness of the sedimentary column across the Delhi Hardwar Ridge. The difference in resistivity may be an indicative of variation in compactness and degree of saturation of the sedimentary cover and the nature of the Indian basement rock across the Delhi Haridwar Ridge.

    • Monitoring agricultural drought using combined drought index in India

      CHATTOPADHYAY N MALATHI K NIVEDITA TIDKE ATTRI S D KAMALJIT RAY

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      Long period data and information indicate that India faced number of droughts-like situation from colonial period. A number of indices have been developed nationally and internationally to monitor agricultural drought based on remote sensing; however, to predict the onset of agricultural drought and its evolution and monitoring in time and space in a more efficient way qualitatively, Combined Drought Index (CDI) has been developed using meteorological, land based and remote sensing observations. In this study, an effort has been made to monitor agricultural drought based on exploitation of new data, methodologies and metrics that would aid the experts to make best judgments of regional-scale drought conditions through CDI using geospatial technology. The present study has been carried out for three consecutive years of 2014, 2015 and 2016 in five states (Andhra Pradesh, Chhattisgarh, Haryana, Maharashtra and Telangana) in India at district level for southwest monsoon season when rainfed kharif crops are grown extensively across the above-mentioned states in India. CDI gives a synthetic and synoptic overview of the drought situations using a classification scheme derived from various individual indices as it has been developed to combine the strength of various indices.

    • Multi-tiered, disrupted crust of a sheet lava flow from the Diveghat Formation of Deccan Traps: Implications on emplacement mechanisms

      GAURI DOLE SHILPA PATIL-PILLAI VIVEK S KALE

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      The crust is a vesicular layer that caps the compact core of sheet lava flows. We describe for the first time, a crust composed of multiple layers (each distinguished by a chilled glassy rind) from the Diveghat Formation in the western Deccan Volcanic Province. The multiple layers of crust developed over a single compact core of a single sheet lava flow, are shown to have been sequentially deformed in multiple phases. This is interpreted to have resulted from the endogenous emplacement of lava in successive pulses (rather than as a continuous stream) during the extrusion of the sheet lava flow. This model has several implications on the mechanism of emplacement of sheet flows in continental flood basalt provinces.

    • A reappraisal of the Jharol Formation in the context of stratigraphy of Aravalli Supergroup, Rajasthan, India

      BHATTACHARYA H N AMRITA MUKHERJEE

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      The enormously thick sedimentary succession exposed between Rishabhdev Lineament and rocks of the Delhi Supergroup constitutes Jharol Formation of the Aravalli Supergroup in Udaipur region of Rajasthan. The whole sedimentary succession is named Jharol Formation and designated as deep water turbidites. A detailed field examination indicates presence of two distinctly different litho successions juxtaposed across a crustal level fault along which brecciated ultramafics are tectonically emplaced. The sedimentary successions exposed immediate west of the Rishabhdev Lineament are deep water sediments with distinct facies types characterizing inner to outer lobe stacked turbidites. These turbidites are similar to the turbidites of the Udaipur Formation and Tidi Formation exposed east of the Rishabhdev Lineament. However, the sedimentary succession exposed west of these deep water sediments across the aforesaid fault contains facies types that represent continental to shallow marine deposits. This basin marginal sediments continue up to the contact with rocks of the Delhi Supergroup. Such litho-association suggests that a separate formation status of the sediments lying west of the Rishabhdev Lineament should be dropped and the turbidites of the Udaipur Formation should be considered as the youngest formation of the Aravalli Supergroup.

    • Geochemistry of the Heavy Mineral Sands from the Garampeta to the Markandi beach, southern coast of Odisha, India: Implications of high contents of REE and Radioelements attributed to Placer Monazite

      SHAYANTANI GHOSAL SUDHA AGRAHARI SANTANU BANERJEE RAMANANDA CHAKRABARTI DEBASHISH SENGUPTA

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      This study presents major element, radioactive element and rare earth element (REE) concentrations of the Garampeta to Markandi beach along the southern coast of Odisha, India to delineate the source signature and resource potential of the beach placer deposits. Average $\sum$REE concentration of the beach sand samples is about four times higher than the average crustal concentration. The LREE concentration is higher than HREE, with a pronounced negative europium anomaly. The study also discusses about the radioelement $^{238}$U, $^{232}$Th and $^{40}$K concentrations in the study area, and their relationship with REE. Weathering condition of the source rock, based on the major elements and Th$/$U ratio indicated a reasonably high degree of weathering. Major element and the REE composition along with the europium anomaly, relate the beach placers to mainly charnockite and khondalite source. An elevated level of thorium (>60 times than the average UCC values) as exhibited by the samples could be attributed due to the presence of monazites. The high concentration of REEs like Nd and Dy along with La and Ce indicates significant REE resource potential in the beach placers which is important for the resource potential in terms of the strategic mineral reserves of the country.

    • Implications of microbial mat induced sedimentary structures (MISS) in carbonate rocks: An insight from Proterozoic Rohtas Limestone and Bhander Limestone, India

      ADRITA CHOUDHURI

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      A variety of microbial mat induced sedimentary structures (MISS) occur in the basal part of the Mesoproterozoic Rohtas Limestone and the Bhander Limestone, India. The combined outcrop and petrographic studies establish unicellular microbial origin of the MISS in the Rohtas Limestone and the Bhander Limestone. Micro-scale deformations associated with MISS imply the late cementation. Paradoxically MISS, once formed, has a better preservation potential in carbonate sediments because of their proneness to get cemented early. The studied basal sections of both the formations built up in a low energy depositional condition. In warm and arid tropical climate, high concentration of dissolved inorganic carbon exacerbated precipitation of aragonite crystals in successive stacks and sulfur concentration led to gypsum precipitation. However, the temperature in the palaeodepositional environment could have been high enough to restrict the sulfur reduction rate severely hampering the growth of sulphur reducing bacteria (SRB) population which was the most powerful post-Archaean calcification engine. The available results indicate Mesoproterozoic palaeotemperature raised up to 32$^{\circ}$C at a mid-latitude location. In the Vindhyan sea straddling across the equator, temperature is predicted to have been considerably higher. The ancient marine limestone formations having MISS, irrespective of their age, developed in similar low palaeolatitudinal locations. Thus, it is reasonable to attribute that high temperature at depositional site cards carbonate sediments to acquire MISS by delayed cementation. Early cementation hinders MISS formation in carbonate sediments, till the sea water temperature crosses an optimal value.

    • Uncertainties in river discharge simulations of the upper Indus basin in the Western Himalayas

      PRIYA P KRISHNAN R MILIND MUJUMDAR

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      This study focuses on understanding and quantifying uncertainties in simulating river discharge in the Upper Indus Basin (UIB) of the Western Himalayas using a macro-scale semi-distributed hydrology model forced with multiple observed precipitation datasets and reanalysis products of near-surface wind-speed, maximum and minimum temperature during 2010–2012. We performed a suite of numerical simulations using a high-resolution setup of the variable infiltration capacity (VIC) hydrology model for the UIB. This model takes into account the balance of both water and surface energy budgets within each grid cell and incorporates sub-grid variability of topography to represent the effects of orographic precipitation and temperature lapse rate essential for hydrological modelling in the complex Himalayan terrain. While river discharges over non-mountainous basins are known to be generally sensitive to precipitation variations, it is noted that both precipitation and snowmelt processes critically influence seasonal river discharge in the UIB during the northern summer through surface temperature and wind-speed variations. Our study found that a marginal difference in temperature forcing can create large difference in snowmelt over UIB during summer season, which in turn increases the uncertainty in the summer monsoon river discharge. This analysis highlights the equally important need for the incorporation of realistic temperature data as that of precipitation product for the better simulation of land surface processes during various seasons, especially during summer, over snow covered UIB. Further analysis of daily simulations of the VIC model during 2010–2012 indicates that low and medium intensity river discharges tend to be associated with relatively lower spread among the ensemble members, as compared to the high intensity discharges which exhibit large ensemble spread. In particular, we noted a large increase in the spread of high flow simulations over the UIB during the flood episodes in the summer of 2010, arising from uncertainties in the precipitation forcing across multiple datasets. Our results emphasize the need for improved representation of precipitation and hydrological processes over the Himalayan region in weather and climate models for better management of water resources and flood forecasting in the UIB region under a changing climate.

    • Time series analysis of climate variables using seasonal ARIMA approach

      TRIPTI DIMRI SHAMSHAD AHMAD MOHAMMAD SHARIF

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      The dynamic structure of climate is governed by changes in precipitation and temperature and can be studied by time series analysis of these factors. This paper describes investigation of time series and seasonal analysis of the monthly mean minimum and maximum temperatures and the precipitation for the Bhagirathi river basin situated in the state of Uttarakhand, India. The data used is from the year 1901–2000 (100 years). The seasonal ARIMA (SARIMA) model was used and forecasting was done for next 20 years (2001–2020). The auto-regressive (p) integrated (d) moving average (q) (ARIMA) model is based on Box Jenkins approach which forecasts the future trends by making the data stationary and removing the seasonality. It was found that the most appropriate model for time series analysis of precipitation data was SARIMA(0,1,1) (0,1,1)$_{12}$ (with constant) and of temperature data was SARIMA(0,1,0) (0,1,1)$_{12}$ (with constant). The model prediction results show that the forecast data fits well with the trend in the data. However, over-predictions are found in extreme rainfall events and temperature results. The information of pattern and trends can assist as a prediction tool for development of better water management practices in the area.

    • Prediction of solar radiation on the horizon using neural network methods, ANFIS and RSM (case study: Sarpol-e-Zahab Township, Iran)

      LEILA NADERLOO

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      Solar energy is one of the clean and healthy energies. Due to the high cost of required equipment to convert solar energy into the desired form, the economic facets must be addressed and the equipment should be installed in areas with higher accessible solar energy. However, due to the complex and time-consuming process of calculating solar radiation, it seems necessary to develop more simple models with higher estimation capability. Therefore, the present study investigated the prediction of solar radiation on the horizon using neural network methods, ANFIS and RSM, in Sarpol-e-Zahab Township, Kermanshah, Iran. In this respect, the meteorological data of this township were collected. Then, the key parameters were selected by performing sensitivity analysis, and models were designed and optimized using ANFIS, ANN, and RSM methods. Moreover, respective correlation coefficients and mean square errors of each method were obtained (ANFIS (0.993 and 0.0005), ANN (0.996 and 0.00029), and RSM (0.996 and 0.00027), respectively). Also, the neural network and response surface methodology were superior to the ANFIS Model in terms of performance, simplicity, and speed. In short, the performance of the response surface methodology was slightly better than that of the neural network.

    • Site-specific probabilistic seismic hazard assessment for proposed smart city, Warangal

      MOHAMMAD MUZZAFFAR KHAN GONAVARAM KALYAN KUMAR

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      In the present work, a probabilistic seismic hazard analysis has been performed for the newly formed Warangal Urban District, Telangana, India. The standard Cornell–McGuire method has been adopted considering different seismic zones. The area of influence chosen is having a radius of 500 km with NIT Warangal as the centre. An earthquake catalogue for the period 1800–2016 AD has been compiled and homogenized using global empirical relationships. Alternative models have been considered for seismic zoning scenario, completeness analysis of earthquake catalogue, maximum magnitude and ground-motion prediction equations (GMPEs) in the logic tree approach by assigning normalized weighs to each model, thereby reducing the epistemic uncertainty. Seismic hazard has been presented as the peak ground acceleration (PGA) and pseudo-spectral acceleration (PSA) maps at 5% damping for spectral periods T = 0.05, 0.1, 0.5 and 1 s at 2% and 10% probability of exceedance in 50 yrs period. The results obtained were compared with IS: 1893-1 (2016) (Criteria for earthquake resistance design of structures, Part-I. Bureau of Indian Standard, New Delhi, 2016) and NDMA (2011) (Development of probabilistic seismic hazard map of India, Technical Report of the Working Committee of Experts (WCE), National Disaster Management Authority (NDMA). Govt. of India, New Delhi, 2011) and they were found to be in excellent agreement. The profile of shear wave velocity (V$_{\rm{S}}$) was obtained by using the multichannel analysis of surface wave (MASW) method. The site was characterized as per NEHRP manual based on V$_{\rm{S}}$. The obtained shear wave velocity values are used in performing the 1-D ground response. A higher PGA has been observed at surface level when compared with the PGA values obtained at rock level suggesting seismic wave amplification due to subsoil condition.

    • Land subsidence mapping and monitoring using modified persistent scatterer interferometric synthetic aperture radar in Jharia Coalfield, India

      SUNIL KUMAR DHEERAJ KUMAR SUMIT KUMAR CHAUDHARY NARENDRA SINGH KAPIL KUMAR MALIK

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      Subsidence has been adversely affecting Jharia Coalfield (JCF) for the last few decades. This study attempts to show the feasibility of the modified Persistent Scatterer Interferometric Synthetic Aperture Radar (PS-InSAR) technique with C-band SAR data to investigate the slow surface deformation caused by coal mine fire and underground mining activities in JCF. Also, a multi-temporal analysis of SAR images of ENVISAT ASAR has been carried out for monitoring and mapping of temporal land subsidence of the area under study. The modified PSI technique has proven its ability to detect land subsidence over the vegetated and rural areas. It also resolves low spatial density of permanent scatterers by considering partially correlated scatterers as permanent scatterers (PSs) and extracting information from these PSs. The study has been concentrated towards detecting continuous slow rate subsidence of five major sites of JCF. The maximum rate of slow deformation among all sites is recorded as 29 mm/year with a cumulative subsidence value of 90 mm. Field validation of subsidence results obtained through PS-InSAR is correlated with the previously published report and the master plan of JCF, showing subsidence locations. Conclusively, the adopted methodology is practically feasible for detection, monitoring and mapping of slow deformation using C-band SAR data in coal mine area.

    • Transport behaviour of different metal-based nanoparticles through natural sediment in the presence of humic acid and under the groundwater condition

      DIBYANSHU TRISHIKHI RAYCHOUDHURY

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      The production of nanoparticles (NPs) has increased significantly, given that they have numerous commercial and medical applications. There might have some risk associated with the release of these NPs in the environment. To assess the possible risk of releases of NPs in the groundwater, it is important to evaluate the fate and transport behaviour of NPs through porous media. The objective of this study is, therefore, to evaluate the transport behaviour of widely used NPs [i.e., silver (Ag), iron oxide (Fe$_{\rm{x}}$O$_{\rm{y}}$), titanium dioxide (TiO$_{2}$) and zinc oxide (ZnO)] through porous media in the presence and/or absence of organic matter [i.e., humic acid (HA)] under controlled de-ionized and natural groundwater condition. To achieve the objective, first, the detailed characterizations of NPs are carried out in the presence and absence of HA. Column transport experiments were performed using a 1-D sand-packed column. Different NPs were injected from one end of the column with a flow rate of 0.0054 cm/sec. The result suggests that nAg, nTiO$_{2}$, and nZnO particles are colloidal stable in the suspension, while nFe$_{\rm{x}}$O$_{\rm{y}}$ particles tend to aggregate and settle down very rapidly. However, in the presence of HA, the colloidal stability of nFe$_{\rm{x}}$O$_{\rm{y}}$ in the suspension increases significantly. Evaluation of transport behaviour of different metal NPs suggests that a high amount of nFe$_{\rm{x}}$O$_{\rm{y}}$ (C/C$_{0}$=0.01) and nZnO (C/C$_{0}$=0.09) particles are retained in the porous media. However, in the presence of HA, the transport efficiency of nFe$_{\rm{x}}$O$_{\rm{y}}$ (C/C$_{0}$=0.64) increases significantly. The extensively high amount of nAg and nTiO$_{2}$ particles are transported in the absence/presence of HA. The surface charge of particles and thus the interaction energy between the NPs and the sand is the main factor controlling the deposition of NPs. Overall, it could be stated that there is a risk of migration of nAg and nTiO$_{2}$ particles irrespective of the presence of organic matter or of nFe$_{\rm{x}}$O$_{\rm{y}}$ particles in the presence of organic matter through the aquifer porous media. However, in the natural groundwater system, when the different ion is present, the extent of transport of NPs is expected to be less, and the risk associated with releasing of NPs in the groundwater would be comparatively low than that is predicted under the controlled de-ionized water condition. However, the nTiO$_{2}$ particles always have a high risk of release into the groundwater.

    • Seismic liquefaction potential assessment of Andhra Pradesh Capital region

      USHA SAI BANDARU VENKATA RAMA SUBBA RAO GODAVARTHI

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      Seismic liquefaction hazard is an actuated ground failure which is responsible for significant damage to life and property. Andhra Pradesh state authorities are aiming to develop major infrastructural projects in the capital region. Liquefaction Potential Index (LPI) can predict the severity of liquefaction at a place. The present work aims at assessing liquefaction severity using LPI for different locations in the new capital region of Indian state, Andhra Pradesh. Further, current study presents a preliminary liquefaction severity map of the Andhra Pradesh state Capital region. This study reveals that the majority of the locations in this region may not be proned to liquefaction in the event of light earthquakes.

    • Geochemical studies of monazites from coastal sands of Kandivalasa–Dibbalapalem coast, Andhra Pradesh

      GANAPATHI RAO P BANGAKU NAIDU K REDDY K S N RAVI SEKHAR CH MURALI KRISHNA K N ANJI REDDY M

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      The present study deals with the geochemical and geochronological studies of monazite from Kandivalasa–Dibbalapalem coast, north Andhra Pradesh. The average concentration of ThO$_2$ and UO$_2$ from beach sands is 11.38 and 0.40 wt.% and from dune sands is 11.94 and 0.63 wt.%. The average REE from beach and dune sands is 58.64 and 57.94 wt.% and they are rich in La, Ce, and Nd. The most common characteristic feature to all monazite shows that the total REE content exceeds that of the actinides (Thru). Monazite that formed after the garnet break down contains significantly higher amounts of Y and HREE in fine sediments. The chondrite-normalized REE distribution patterns of monazite show uniformly enriched light rare earth element ($\sum$LREE) which could be due to the preferential incorporation of lighter lanthanides and positive europium anomalies indicate that monazite was formed from magma/anatectic melt with high oxygen fugacity. Back-scattered electron (BSE) images of monazite showing compositional zoning and the bright outermost rim which is attributed to the influence by variations of LREE, HREE, U, Th, Pb and Y concentrations. The primary controlling factor, radiation damaged monazite yields in most cases significantly, with a strong dependence on the degree of metamictization based on the BSE intensity. The geochemical dating (U–Th–Pb) of monazite ranging age from 487 to 977 Ma from grain interior, can signify the age of Grenvillean evolution. This interpretation changes the existing tectonothermal history of the northern Eastern Ghats Belt. Our data show that the two adjacent crustal domains of the Eastern Ghats Belt show distinctly contrasting Neoproterozoic histories.

    • Curvature interpretation of gravity data for delineating structural features across the transition zone of Narmada–Son lineament in central India

      GHOSH G K

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      Potential-field anomalies can be converted to a common function which describes the ridge, peaks over an isolated source. In this study, attempt has been made to interpret curvature attributes of equipotential surface using gravity gradients for delineating thrust–fault locations in one of the seismically active transition zones of Narmada–Son Lineament (NSL) in central India. The NSL is oriented in the ENE–WSW direction, divides the area into two geological provinces. The northern part of this NSL comprises Vindhyan formations and southern part covers Gondwana formations. It has been observed that, the northern part (around Jukehi) of the area has higher elevation with lower gravity anomaly and the southern part (around Khamaria and Kataria) has lower elevation with higher gravity anomaly. The tectonic activities like intrusions, volcanisms and earthquake occurrences were the sources of crustal resettlement during the past in this area. Various researchers commented about the structural configuration; however, the present study helps to understand the structural features using various curvature analysis like maximum, minimum, most-positive, most-negative, mean, dip (profile), strike (tangential), contour (plan), curvedness, shape index and Gaussian curvatures. Out of these curvatures most positive, maximum, mean, dip and curvedness show more effective results compared to other curvatures. However, shape index states domes, ridge, flat, valley, bowl shape type structures. The results are also correlated with the conventional horizontal gravity gradient, analytic signal and tilt derivative analysis. The colour contrast variation of these differential curvatures make in-depth understanding with extensive multiplicities of integrity for delineating subsurface structures.

    • Characterization of bioaerosols in Northeast India in terms of culturable biological entities along with inhalable, thoracic and alveolar particles

      BINITA PATHAK DEBAJIT BORAH ANKITA KHATANIAR BHUYAN P K BURAGOHAIN A K

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      Effort was made to analyse the biological components along with inhalable, thoracic and alveolic particles in aerosol samples collected from nine distinct locations of Northeast India during post-monsoon season (October–November) for the very first time. Microscopic analysis reveals the presence of 70–90% of non-biological particles followed respectively by pollens (9–18%), animal debris (1–12%) and fungal spores (1–6%). The concentration of bacteria in air sample ranges from 45.5 to 645.84 CFU/m$^{3}$. All the bacterial isolates showed sensitivity against broad (Chloramphenicol and Ampicillin) and narrow (Vancomycin and Erythromycin) spectrum antibiotics which indicates lesser threat to human health. Moreover, the concentration of microbial content in the bioaerosol samples are less compared to some of the reported values in other parts of India. The predominant microbial genera in the collected bioaerosol samples were identified as Gram positive Diplobacilli sp. followed by Diplococci sp. Pollens of 10–20 $\mu$m diameter, which are mostly considered as potential allergens, contribute only up to 20% of total pollen content in the bioaerosol sample collected from various locations indicating healthier air.

    • Behaviour of contaminant transport in unconfined coastal aquifer: An experimental evaluation

      BHRIGUMANI SHARMA RAJIB KUMAR BHATTACHARJYA

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      Contamination of groundwater in coastal aquifers is a significant environmental concern for coastal populations across the world. As it not only leads to the depletion of available freshwater resources, but also threatens the ecology and economy of the coastal zones. A quantitative understanding of contaminant transport processes within coastal aquifer systems is, therefore, essential for efficient planning and management of coastal environments. The overarching aim of this research is to investigate the behaviour of contaminant transport patterns for various contaminant transport scenarios in a coastal unconfined aquifer. For this purpose, a series of laboratory-scale experiments have been carried out in the setup of a rectangular flow tank using dye to trace the movement of contaminant plume patterns with homogeneous soil formations. The experimental data indicate that the contaminant travels upward towards the seaward boundary when it approaches the saltwater wedge and then exits around the coastline. Upon installation of the pump, the saltwater intrusion wedge was moving rapidly towards the freshwater aquifer, and the contaminant was also moving along with the saltwater wedge towards the pump location. Experimental results also clearly show that the contaminant plume formed an elongated shape as it approached the saltwater–freshwater interface due to dispersion effects. The findings from this experimental study helped us to have a better understanding of the contaminant transport processes occurring in a coastal unconfined aquifer.

    • Local effects of wind turbines on near-surface wind speed in a desert steppe wind farm

      DANDAN ZHOU SHENGRONG HU XIAOHONG DANG JINRONG LI CHUNXING HAI YUHAI BAO JING ZHU

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      This research describes and interprets spatial variation in near-surface wind speed around a large scale wind generation operation in a desert steppe environment of Inner Mongolia. Wind speeds were measured at five different heights and distances in front of and behind turbines and compared to that measured simultaneously from reference points immediately outside of the wind farm. The results showed that wind turbines clearly influence the spatial distribution of near-surface wind speed. Relative to reference points, near-surface wind velocity profiles measured at various distances from wind turbines followed a logarithmic distribution. The correlation coefficients for all points were above 0.95 except for a coefficient of 0.8278 corresponding to wind speeds measured 20 m in front of turbines. The wind speed increment rate at 20, 100, and 300 m in front of and behind turbines demonstrated the varying influence of turbines at different points. The area 100 m behind the turbine experienced maximum wind speeds at all height levels observed in the measurement area. The overall wind speed at 300 m distance was relatively low and variation nearest to the turbine was the most complex.

    • Evaluation of the convective mass flux profiles associated with cumulus parameterization schemes of CMIP5 models

      PARTHASARATHI MUKHOPADHYAY KUMAR ROY

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      While the numerical models are being run with increasing resolutions, the parameterization of cumulus convection used in the general circulation models, irrespective of closure assumption and trigger mechanism, continue to use the mass flux framework. To address one of the most important components of convective parameterization, vertical profile of mass flux is examined. We have compared the convective mass flux of the Coupled Model Intercomparison Project Phase 5 (CMIP5) models during Boreal summer over the Eastern Pacific, Western Pacific and Indian Ocean with that of ERA – Year of Tropical Convection (YOTC) reanalysis dataset. The analyses suggest that most of the models overestimate the mass flux by an order over all the oceanic basins and interestingly the vertical structure also appears similar for all the CMIP5 models irrespective of ocean basins. In view of this, we state that the improper mass flux distribution in the cumulus parameterization schemes of global models need to be improved to reduce some of the uncertainties arising from the cumulus schemes of climate models which in turn impact the precipitation bias of the models.

    • Carbonate hosted intermetallic compounds in Paleoproterozoic Salumber Ghatol metallogenic belt, Aravalli Craton, Rajasthan, India

      SURESH CHANDER AUSAF RAZA SANTANU BHATTACHARJEE SANJAY DAS

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      Carbonate hosted intermetallic compound in the Umarvaniyan area is localized within the intensively sheared (mylonitised) dolomite in a NW–SE shear zone ($\sim$15 km), belongs to Salumber Ghatol metallogenic belt, in Debari Group of Aravalli Craton, Rajasthan, India. It is characterized by extensive silicification and ferruginisation with hematite, goethite, magnetite and native gold specks. The intermetallic compound within the dolomite is composed of varying proportion of Cu–Zn–Ni–Os–Fe which has been detected by electron probe microanalysis (EPMA) study. The EMPA (WDS) results of the intermetallic compounds also reveal occurrences of intermetallic compounds of Cu–Zn–Ni–Os–Fe and native Au. The occurrence of these non-separable compounds is probably because these metals were formed at very high temperatures and in reducing condition during the evolving shear with low oxygen and low sulfur fugacity. The fast cooling effect thereafter probably made the geochemical environment least conducive for reaction between Cu/Zn/Ni and sulphur or oxygen.

    • Enhancement of a thumper source far oAset refracted phases using super virtual interferometry (SVI)

      VAIBHAV JAIN DIBAKAR GHOSAL SHASHANK NARAYAN VERMA

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      Super-virtual interferometry (SVI) is a technique in which cross-correlation between consecutive receiver responses is carried out to obtain the virtual head-wave arrivals, which are then convolved with the initially recorded traces to get the super-virtual trace. SVI can be used to enhance the refracted phases by stacking all the arrivals acquired using multiple shots at one position, leading to an improved SNR by a factor of $\surd n$, where $‘n’$ is the number of sources and receivers to generate the head-waves. In this study, we have generated few synthetic common shot gathers (CSGs) using forward modelling over a three-layer velocity–depth model with an embedded spherical anomaly, a complex five-layer velocity–depth model and the Marmousi model. Certain amount of noise is added on these gathers and then SVI technique is applied on the gathers which has resulted in an improved SNR of refracted phases at the far offset. We have further tested this technique on a field dataset acquired from the Kumaon Himalayan region using a 450 kg thumper as an energy source and 111 active channel remote acquisition unites (RAUs) with 5 Hz geophones as sensors. The resulting SVI gathers show the refracted arrivals more clearly. Continuity in the phases is increased after stacking and iterative SVI.

    • Slope stability analysis and mitigation measures for selected landslide sites along NH-205 in Himachal Pradesh, India

      AKHILESH KUMAR RAVI KUMAR SHARMA BIKRAM SINGH MEHTA

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      Landslide is the most frequent geo-environmental natural hazard which significantly affect human life and environment. It is the natural hazard when occurs especially in hilly regions mainly along highway corridor, results in obstruction to traffic flow. The road network of a developing country plays a vital role in its overall development. Therefore, it is important to ascertain landslide hazard assessment along roads. In this regard, the study was carried out in middle Himalayan region of Himachal Pradesh, India. The paper describes the investigations carried out on two major landslides, namely Panjpiri and Nalayan occurred at Kiratpur Sahib to Nauni road stretch along NH-205 in Himachal Pradesh, India. The slope failure occurred at Panjpiri was identified as plane failure, whereas at Nalayan it was circular failure. The factor of safety was determined by using Bishop’s method of slices and circular failure charts. For factor of safety calculation of Panjpiri plane failure, six conditions were considered based on physical attributes. Subsequently, the evaluation of slope was designed by reinforcement with rock bolts. While for Nalayan circular failure, soil anchors were designed. Thus, evaluation of slope stability of these two failed slopes were carried out for suggesting appropriate mitigation measures. The results of the study conclude that, with an accurate and well-planned mitigation measures, the severe landslide susceptible sites can be stabilized. Adopting effective engineering mitigation strategies may help the decision makers to choose the appropriate strategies to minimize the landslide hazard.

    • Characterization of the interannual variability of precipitation and runoff in the Cheliff and Medjerda basins (Algeria)

      ABDERRAHMANE KHEDIMALLAH MOHAMED MEDDI GIL MAHE

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      An analysis of rainfall and hydrometric regimes was carried out over the period from 1968 to 2013 on the Cheliff basin situated in the west and the Medjerda basin in the east of Algeria. The Mann–Kendal and Pettitt tests have shown significant downward trends for rainfall, about 30% for the Cheliff basin, and 36% for the Medjerda basin, and about 61% and 43% for the Cows at the level of the Cheliff and Medjerda basins, respectively. The continuous wavelet method, used during the study period, has shown three major discontinuities from the wavelet spectrum for the decades 1970s, 1980s and 1990s. Several modes of variability for different stations have been observed: annual (1 yr), interannual (2, 2–4 and 4–8 yrs), and multi-decadal (8–16) yrs. The different scales of precipitation and runoff variability seem to be clearly related to the NAO with different degrees of correlation. Continuous wavelet coherence indicates a strong correlation between the NAO climate index and precipitation with correlations ranging from 60 to 84%, and a strong relationship between the NAO and the runoff with correlations ranging from 67 to 74% for both watersheds.

    • Magnetotelluric study of an intraplate seismic zone in the Palghar region of the Deccan Volcanic Province, India

      G PAVANKUMAR N N CHAKRAVARTHI M DEMUDU BABU A MANGLIK

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      The Deccan Volcanic Province in the western part of the peninsular India consists of a thick pile of flood basalts resting mainly on the Archaean and Proterozoic rocks forming the basement. This intraplate region experiences moderate seismic activity, the most recent one being a swarm-type activity in the Palghar region, about 120 km north of Mumbai, that started in November 2018 and has produced a few thousand micro-earthquakes and a 4.3 magnitude earthquake since then. We have carried out a magnetotelluric (MT) study along a 35-km long profile across the seismic zone to delineate the subsurface structure to understand the possible cause for the seismic activity. Broadband MT data were acquired at 18 sites with average station spacing of 2 km. Impedance tensors were analyzed for distortion and dimensionality, decomposed into TE- and TM-mode, and inverted by a 2D inversion algorithm. The geoelectric structure yields an assemblage of highly resistive and moderately conductive blocks in the uppermost crust resting on a major listric-type fault, that possibly reaches the surface at the West Coast Fault from a depth of about 15 km beneath the Panvel flexure zone. In conjunction with the regional Bouguer gravity anomaly and the seismicity distribution, we infer that the upper crustal heterogeneities coupled with the basement fault and low rheological strength of the fractured upper-to-middle crust might be leading to triggering of the seismicity in the region.

    • Stability analysis of road cut slope near Devprayag in Lesser Himalaya, India

      TARIQ ANWAR ANSARI K H SINGH T N SINGH JAYANT NATH TRIPATHI

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      The slope instability issues in Himalayan terrain is drastically increasing due to variety of anthropogenic activity and rapid urbanization. Road and highway networks in mountainous regions are the main source in remote parts of hilly terrain for the transportation as well as all sorts of socio-economic features. The study of slope stability in these hilly regions along the highways and roads are major concern, where slope instability caused transportation problems, death and injury of human, loss of their properties and also environmental degradation. Present article exposed the slope instability analysis for the two typical slopes along National Highway (NH-7), between Devprayag and Mulyagao in Uttarakhand, where the Highway goes up to the holy shrine of Kedarnath and Badrinath. The vulnerable slopes are numerically simulated using limit equilibrium method (LEM) and finite element method (FEM) for dry and saturated condition. The comparative analysis of factor of safety for LEM and FEM results show good correlation, i.e., 1.6–2.4% variance in dry condition and in saturated condition the LEM and FEM results show 11–13% variance. The finite element simulation has also assessed the principal stresses and displacement vector, which gives more understanding to identify and reveal the slope stability issues in analogous morphology. The result shows that both the slopes are in critical condition and prone to failure in rainy season due to exertion of water in intensely fractured rocks.

    • Characteristics of convective/stratiform dominance on surface rainfall over a few tropical locations

      RAJASRI SEN JAISWAL SIVA M RASHEED M THIRUMALA LAKSHMI K

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      To understand rainfall dynamics, the characterization of convective and stratiform dominance needs a careful investigation. However, it remains a grey area to date. In this paper, the authors have attempted to differentiate between convective and stratiform events based on vertical profiles of a few upper-air meteorological elements, namely, cloud liquid water (CLW), precipitation water (PW), and latent heat (LH). The parameters have been obtained from the data product 2A12 of the Tropical Microwave Imager (TMI) onboard the Tropical Rainfall Measuring satellite (TRMM). The paper presents the demarcation technique between convective and stratiform dominance on surface rainfall without ambiguity

    • Grounded electrical source ground–airborne transient electromagnetic modelling with Bctitious wave Beld methods

      XIANGDONG MENG SHILIN QIU YANJU JI

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      The finite-difference time domain (FDTD) method is widely used in ground–airborne transient electromagnetic modelling. Generally, this method offers great limitations because the calculation of the air layer is avoided and the surface assumption is Cat. This study proposes a new method for ground–airborne 3D electromagnetic forward modelling that includes air layers and effectively solvesthe airborne TEM forward calculation of the coastal ocean and rugged terrains. The optimum selection of the air-layer resistivity and the identification ability of the long-wire source are discussed. By adding the pulse source signal to the control equation and realizing a direct calculation that includes the source, the cumbersome process of calculating the complex initial field is avoided. After establishing the mountain model and coastal ocean model, the electromagnetic response is discussed. Subsequently, the ground–airborne TEM modelling is subjected to a 3D numerical simulation of complex geological conditions. The validity of this method is verified by analytical solutions through a uniform half space. The results show that the method can achieve 3D and high-precision numerical calculations when it includes complex terrain and seawater.

    • Evaluation of ESACCI satellite soil moisture product using in-situ CTCZ observations over India

      SHUBHI AGRAWAL ARINDAM CHAKRABORTY

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      Recently available European Space Agency Climate Change Initiative (ESACCI) soil moisture dataset, derived by merging soil moisture values calculated using measurements from satellite-based active and passive sensors, is validated over the Indian region using in-situ observations from 117 Continental Tropical Convergence Zone (CTCZ) Programme stations spread across India. The dataset is compared for the monsoon season (June–September: JJAS) of two years – 2011–2012, over six regional domains which differ in soil characteristics and mean soil moisture values, thus taking the spatial heterogeneity into account. Evaluation shows that the mean JJAS ESACCI volumetric soil moisture is $25.5% (\rm{m^{3} m^{-3}})$, with an intra-seasonal standard deviation of 6%. The root mean squared difference (RMSD) between ESACCI soil moisture product and CTCZ observations is 10% over the Indian region. Over smaller homogeneous regions, the RMSD values between the two products are smaller than 5%, except over southern India and north-east India. Overall, the ESACCI soil moisture dataset is in good agreement with the CTCZ in-situ soil moisture observations, and has relatively higher accuracy over the plains of northern and central India, as compared to other regions. However, the ESACCI soil moisture dataset shows higher intra-seasonal variability at shorter time-scale of 2–4 days, as compared to the CTCZ observations, possibly due to the difference in the soil sampling depths between the two datasets.

    • Timing and cause of the disappearance of some elongated taxa in the Indian Ocean: Study from NGHP Hole 17A

      SANJIB BISWAS AJOY K BHAUMIK

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      Disappearance of many elongated benthic foraminifera across the Mid-Pleistocene Transition (MPT) is popularly known as ‘Stilostomella extinction’. This event is reported from several sites across the world and it is believed that most of the elongated benthic families disappeared within 0.76–0.5 Ma. It is assumed that the presence of cold bottom water triggered their disappearance. The present study is pursued on sediment cores collected from National Gas Hydrate Program Hole 17A, Andaman Sea, Indian Ocean to examine the precise timing and cause of the disappearance of elongated taxa as well as their ecological preference. Our study reveals that elongated species prefer warm and low to intermediate food condition. This study documents the disappearance of 5 major species and 13 minor species from 0.6 to 0.2 Ma which is younger than the earlier estimates. We assume that change in 41–100 kyr climatic cycle along the MPT was responsible for a major decline in their number. However, amplified glacial–interglacial cycles along Mid-Brunhes (0.5–0.2 Ma) finally played a major role in their disappearance. Both of these consecutive events extended intensified cooling and dropped the deep-ocean temperature by which the shallow infaunal elongated species disappeared and deep-infaunal species survived.

    • Antarctic ice-shelf thickness changes from CryoSat-2 SARIn mode measurements: Assessment and comparison with IceBridge and ICESat

      BAOJUN ZHANG JINGBIN LIU ZEMIN WANG TINGTING LIU QUANMING YANG

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      Ice-shelf thickness changes are of critical importance for understanding the stability of the Antarctic ice-sheet because they restrain the seaward flow of grounded glaciers. In this study, we find that neither backscatter nor leading-edge width contained in the least-squares fitting model can improve the accuracy of ice-shelf thickness change estimations from CryoSat-2, which is validated by comparing the CryoSat-2-derived elevation changes from least-squares fitting models with different combinations of waveform parameters against the Operation IceBridge ATM L4 data. Using the model without backscatter and leading-edge width to infer the thickness changes in Antarctic ice shelves from CryoSat-2, we find that the most significant thinning signals are mainly concentrated on the ice shelves along the Amundsen Sea coast, such as Getz, whose thickness variations are dominated by ocean-driven basal melting. This phenomenon has also been confirmed by the ICESat results. Overall, the Antarctic ice shelves volume changed on average by $–0.34 \pm 66.36 \rm{km^{3} yr^{-1}}$ during the period from July 2010 to December 2016.

    • ModiBcation of pre-existing folds in a shear zone: A case study from Kumbhalgarh–Ranakpur area, South Delhi Fold Belt, Rajasthan, India

      KALYANBRATA HATUI ANUPAM CHATTOPADHYAY

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      Pre-existing structures (e.g., folds, foliations, lineations) are usually rotated and modified within a shear zone, depending on their attitude with respect to the kinematic framework (i.e., orientation of instantaneous stretching axes (ISA), kinematical vorticity number of the flow ($W_{k}$)) of the shear zone. In addition, new folds may also form within a shear zone, and it is not always easy to distinguish between the pre- and syn-shearing structures in the field, especially if they form on the same rock type. The present contribution describes the reorientation and shape modification (tightening) of pre-existing and synshearing folds in metamorphosed calcareous rocks of the Kumbhalgarh Group (part of Delhi Supergroup) due to shearing along the Ranakpur Shear Zone (RSZ), in Kumbhalgarh–Sayra–Ranakpur area of South Delhi Fold Belt (SDFB), also called South Delhi Terrane (SDT). From field-based study and measurements, it is shown that the shallow-plunging, upright second generation ($\rm{DF}_{2}$) folds of SDFB/SDT have been rotated to subvertical, tight folds within the RSZ. Fold shape analysis using layer thickness and limb dip of folds (i.e., Ramsay’s classification) and by Fourier transform shape analyses of fold profile sections corroborates and roughly quantifies the tightening and shape modification of pre-existing folds within the RSZ. In contrast, syn-shearing folds have formed on the foliations in calc-silicate rocks which show strongly non-cylindrical geometry with apical defection in an oblique direction. From the available shear sense indicators like rotated porphyroclast tails and vergence of asymmetric folds, the shear sense of the RSZ is interpreted as oblique reverse (east-side-up) with subordinate sinistral (east-towards-north) shear component, which is similar to the shear sense interpreted by some earlier workers.

    • Mixed carbonate–siliciclastic sedimentation in the Upper Cretaceous Nilkanth Formation, Garhwal Himalaya, India

      SHRUTI R MISHRA ADITI SHARMA PARTHA P CHAKRABORTY SARADA P MOHANTY SATISH C TRIPATHI

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      The Upper Cretaceous Nilkanth Formation awaits a process-based depositional model despite being a topic of discussion between stratigraphers, palaeobiologists and structural geologists over the last few decades. Sedimentary facies analysis of a $\sim$50 m thick section along a $\sim$2.8 km long section along Rishikesh–Tal Bidhashini in Pauri Garhwal district of Uttarakhand allowed documentation of mixed carbonate–silicicalstic facies types, dominantly consisting of sand- and pebble-sized carbonate debris mixed with siliciclastics in a proximal to distal facies tract. Ten different facies types that include matrix rich and matrix-poor shelly conglomerate, mixed clastic-carbonate wackestone, packstone, impure calcirudite and calcarenite, biomicrite and ferruginous sandstone are documented. Delineation of facies association and documentation of facies stacking pattern provide a post-Santonian mixed carbonate– siliciclastic sedimentation history of the Nilkanth Formation, deposited in the form of mass flows of varied rheology on a barred low- to moderate-gradient carbonate ramp, formed at the leading edge of the India plate before its collision with the Kohistan–Ladakh arc. Carbonate clasts comprising bivalves, crinoids, algae, bryozoan, etc., were produced in a narrow high-energy transgressive coastline and supplied across shelf along with reworked siliciclastics from clastic shoreface bar. It is argued that the reworked fossils, including the bryozoa Ceriocava Nilkanthi, present within massflows may not justify fixing of an absolute age for the formation but may definitely help in providing an age range.

    • Dynamic recrystallization mechanisms and vorticity estimation of the Terrane Boundary Shear Zone (Lakhna shear zone): Implications on dynamics of juxtaposition of the Eastern Ghats Mobile Belt with the Bastar Craton, NW Odisha

      BHUPESH MEHER BHUBAN MOHAN BEHERA TAPAS KUMAR BISWAL

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      The Terrane Boundary Shear Zones provide important information regarding tectonics of juxtaposition between different terranes. In this paper, we have studied the Lakhna shear zone, between the Eastern Ghats Mobile Belt and the Bastar Craton. Detailed structural study, sampling and strain analysis through measurement of size and orientation of dynamically recrystallized quartz grains indicate: (i) the Lakhna shear zone is developed on granitic protolith of the Bastar Craton, (ii) mylonites are quartzofeldspathic in composition, marked by SE dipping mylonitic foliation and down dip stretching lineation defined by biotite and quartz grains, (iii) S-C fabric and rotated porphyroclasts indicate a NW vergence thrust kinematics, (iv) recrystallization of quartz grains occurred by climb-assisted dislocation creep through BLG near craton boundary, SGR in the central part of the shear zone, GBM towards the Eastern Ghats margin, (v) temperature of deformation increases towards mobile belt ($380–560^{\circ}\rm{C}$) that suggests thrusting of granulitic hot slab over cold craton and (vi) $W_{m}$ estimates of 0.9 suggest simple shear deformation. The juxtaposition between the EGMB and the Bastar Craton occurred by simple shear thrusting when the granulitic slab was hot enough to create a difference in temperature and mechanism of dynamic recrystallization across the shear zone.

    • Rejuvenation of ‘pop-up’ tectonics for Shillong Plateau in NE Himalayan region

      PARTHA SARKAR P N S ROY SANJIT KUMAR PAL

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      Seismicity variation along with crustal heterogeneity using natural source is of prime interest in advance research nowadays. In the global scenario, North-East India is one of the prominent seismicity active zone characterized by its tectonically complex set-up. The seismicity study area encompasses between $\rm{18^{\circ}–32^{\circ}N}$ latitude and $\rm{88^{\circ}–102^{\circ}E}$ longitude, which basically locates the Shillong plateau and its surrounding in north-east part of India. Here, we have attempted to forecast the seismicity pattern as well as the crustal heterogeneity for Shillong plateau in north-east part of India. In this regard, we have used the most basic seismicity parameter like $b$ value and fractal correlation dimension ($D_{c}$) along with focal mechanism characteristic over the entire region of study. The correlation experiment between the lower $D_{c}$ value and $b$ value indicates the possibility of an earthquake of large magnitude in the south central Burma basin and Shillong plateau region. Various dynamic faults and associated seismicity spread over all around the North-East India supports the possible rejuvenation of pop-up structure for Shillong plateau. We have tested our proposed method on real dataset, presented and analysed our experimental results and compared it with other methods and the overall results are found to be satisfactory.

    • Analysis of summer monsoon rainfall over Maharashtra and its relation with SSTs

      JASMINE TAKLE D S PAI

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      This paper is based on the spatio-temporal analysis of daily, monthly and seasonal rainfall variability over Maharashtra state of the Indian region, for the period 1901–2017 during summer monsoon, viz., June through September. This analysis is carried out over Maharashtra’s four sub-divisions, where mean rainfall received for JJAS (1901–2017) is more over Konkan and Goa and east Vidarbha and less over Madhya Maharashtra. Coefficient of variation is considered to understand spatial variability of total rainfall received during JJAS by the state. The percentage of rainy days is found to be more for July and August months compared to June and September months as per the advancement of monsoonal flow noticeable through this study. Hence, contribution to JJAS rainfall more from July month proceeded with August month is considerable. September month contribution is the least; nevertheless its contribution is prominent from south Madhya Maharashtra. Rainfall variability is linked with El Nino and La Nina, by calculating composites of standardized rainfall anomalies and % rainy days during El Nino and La Nina years, which show that monthly and seasonal rainfall, are modulated by variations in SSTs of equatorial central Pacific Ocean. Thus this study aims to analyze the changing pattern of rainfall over Maharashtra and its sub-division as linking El-Nino and La-Nina events with rainfall received over small domain is the need of the hour as each region behaves differently during El-Nino or La-Nina.

    • Characterizing the source of a prominent magnetic anomaly in the southwestern part of the Cuddapah basin

      D SESHU M PRASANTHI LAKSHMI S PARVEEN BEGUM A MANGLIK

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      The total magnetic intensity anomaly (TMI) map of the Proterozoic intracratonic Cuddapah basin shows the presence of a prominent high–low–high anomaly of about 600 nT amplitude at its southern end. The source of this anomaly is inferred to be a mafic intrusive body due to a thermal plume that might have initiated the basin evolution. Though some quantitative studies have been carried out over this anomaly, the magnetic body remains ambiguous as only a part of this anomaly was modelled along the E–W direction. In present study, we model this anomaly by a 2.5D algorithm and analytical signal of the vertical integral (ASVI) of the TMI approach. A near circular outline of the causative body has been delineated by the analysis of ASVI, which also revealed three characteristic zones of the near surface irregularities. The 2.5D modelling along a SW–NE profile across the anomaly yielded the main body of about 10 km wide top at 3.5 km depth and 40 km wide at 25 km depth. The Curie temperature depth in this region is 30–40 km and this allows the source to be magnetic at this depth. It is inferred from both ASVI and modelling that the main body is bifurcated into two in its south-western part between Parnapalle and Muddanuru while it attains a lopolithic shape over the remaining part. Existing regional aeromagnetic data elucidates shape of the mafic intrusive both laterally and vertically.

    • Detection of Cash-Cood potential areas using watershed characteristics: Application to Cau River watershed in Vietnam

      LOI DUONG THI THANH DO VAN HUONG LE VAN

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      The main purpose of this study is to detect flash-flood potential areas based on the pre-event characteristics in the study area. Five physical factors including slope, land use, soil texture, tree canopy density, and drainage density were used to create index maps in the Geographic Information System (GIS) environment. Each index was classified from 1 to 10 by identifying their influence levels with the presence or absence of flash floods based on the Flash Flood Potential Index (FFPI) model. As the result, the most susceptible areas were given a value of 10 and the least susceptible areas were given a value of 1. These indices were then mapped and integrated into a weighted linear model. Analytic Hierarchy Process (AHP) was used to determine the weighted correlation among elements based on their importance to this phenomenon. Weighted Flash Flood Potential Index (WFFPI) map was classified into four levels, including very high, high, moderate, and low flash flood potential. The result shows that more than 10% of the total area has the greater possibility to be affected by a high-intensity flood, and distributed at the north and northeast mountain ranges while most of the area is at a medium value with 84.35%. Finally, the similarity between results in this study and reference results from HEC-RAS model showed the reliability of the applied method.

    • Mapping of laterite zones using 2D electrical resistivity tomography survey in parts of Paschim Medinipur, West Bengal, India: An approach for artificial groundwater recharge

      K PRATIMA PANDA AKANKSHA UPADHYAY M K JHA S P SHARMA

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      Earth’s most valuable and renewable resource ‘groundwater’ is depleting rapidly in the last few decades. Due to lack of proper usage and planning of groundwater leads to water scarcity in some problematic areas of Paschim Medinipur, West Bengal, India. The presence of impervious laterite on the surface as well as in the subsurface is the main problem that hinders the natural groundwater recharge in the area. To overcome this issue, artificial recharge of groundwater and rainwater harvesting can be the best solutions. However, this requires precise information about the subsurface structures. Therefore, 2-dimensional Electrical Resistivity Tomography (ERT) surveys are performed at nine locations (separated by 3–4 km distances) covering a distance of about 30 km along a profile in E–W direction centrally located between Kangsavati (in the north) and Subarnarekha (in the south) rivers. The present study area extended between Village Chirakuti in the west to Village Nandakishorpur in the east, in the Paschim Medinipur district of West Bengal. A principle profile line of 30 km with a station interval of 3–4 km is covered along east–west direction. 2D data is collected at nine locations (with 800 m spread) along the principle profile. Every dataset is interpreted using RES2DINV software. The study reveals that the observed resistivity is highest in the western part ($1400 \Omega\rm{m}$) and lowest in the eastern part ($40 \Omega\rm{m}$) of the principle profile. The 2D interpreted resistivity cross-sections reveal that, the western part of the principle profile has conductive layers overlaid by a resistive layer on the top. The eastern part of the principle profile represents Cat younger alluvium deposits. Most of these sediments are clayey sand, coarse sand on top and hard clay, small gravels to 10 mm gravels in deeper parts. The water crisis is mainly in the western part. So puncturing the top laterite layers and allowing the run off water to penetrate into the subsurface may solve the problem. Building watersheds for agriculture in the western part of the principle profile line could help in increasing of the groundwater level in the study area.

    • Iron-nickel metallic components bearing silicate-melts and coesite from Ramgarh impact structure, west-central India: Possible identification of the impactor

      DWIJESH RAY SAUMITRA MISRA DEWASHISH UPADHYAY HORTON E NEWSOM ERIC J PETERSON ANAND DUBE MANAVALAN SATYANARYANAN

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      The Ramgarh structure (rim-to-rim diameter $\sim$2.4 km) in the Vindhyan Supergroup of sedimentary rocks (including sandstone, shale and minor limestone) of the Mesoproterozoic age in the west-central India, is India’s third confirmed asteroid impact crater. This eroded structure is roughly rectangular in shape and resembles to the Barringer Crater, USA. The presence of central peak and its current crater diameter/depth ratio of $\sim$12 well corroborate the range (10–20) of terrestrial complex asteroid impact craters. The mm-sized, iron-rich (FeO $\sim$50 wt.% in average), spherule-like particles, recovered from the alluvium inside the Ramgarh structure, have internal morphology similar to those of the accretionary lapilli described in known impact craters. The in-situ LA-ICP-MS analyses also suggested high Co–Ni (up to 13,000 and 2500 ppm, respectively)-rich areas locally within these spherules/lapilli. A few non-in-situ, mm-sized particles, recovered from the rim of the structure show the presence of coesite, one of the diagnostic indicators of shock metamorphism. A few fragments of iron-rich, Ca–Al–silicate glasses recovered from the soil inside the structure and outside of the western crater rim include the presence of dendritic magnetite with occasional inclusions of relict native iron. Our microprobe analyses confirm that these metallic irons contain high proportions of Co ($\sim$350–3000 ppm), Ni ($\sim$200–4000 ppm) and Cu ($\sim$2200–7000 ppm) and possibly could be the relict component of a Cu-rich iron meteorite impactor. The field observation and relative enrichment of compatible and incompatible trace elements in the spherule-like substance (recovered from the alluvium inside the Ramgarh structure) as compared to target rocks suggests that hydrothermal activity played an important role in the evolution of the crater.

    • Trace and REE geochemistry of bauxite deposit of Darai–Daldali plateau, Kabirdham district, Chhattisgarh, India

      BHUMIKA DAS M W Y KHAN HARISH DHRUW

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      The Darai–Daldali plateau preserves well developed laterite type bauxite deposits as a result of in-situ weathering of basaltic rocks (Deccan Traps). The bauxite ore is essentially composed of gibbsite and boehmite in subordinate amount, along with anatase and brookite as accessory minerals. Kaolinite, goethite, hematite, ilmenite, gibbsite and brookite are found in lateritic bauxite and laterite samples invariable amounts. $SiO_{2}–Al_{2}O_{3}–Fe_{2}O_{3}$ diagram illustrates strong bauxitization resulting from desilication in the early stage. The disilication was followed by bauxitization and deferruginization at late stages as a result of reducing and oxidizing conditions, respectively, due to fluctuating water table, which is evidently supported by A–L–F plot. Progressive loss/gain in FMTE, LILE, HFSE and REE during bauxitization process of basalt through lateritic bauxite facies is observed. La/Y varying from 1.17 to 4.11 suggests prevalence of alkaline conditions. Positive Eu/Eu* anomaly in these samples is suggestive of colloidal precipitation of gibbsite from pore water of lateritic residuum. Mass increase of Ce in laterite samples further supports to its sorption on goethite and hematite mineral phases.

    • Evaluation of SP-CAM and SP-CCSM in capturing the extremes of summer monsoon rainfall over Indian region

      TANMOY GOSWAMI BIDYUT BIKASH GOSWAMI R PHANI MURALI KRISHNA PARTHASARATHI MUKHOPADHYAY

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      The simulation of the Asian monsoon rainfall and its extreme events with high fidelity remains a challenge even for the present day state-of-the-art models with conventional treatment of convection. A multi-scale approach vis-a-vis the super-parameterization appears to overcome the uncertainty of convective parameterization and thereby improve models ability to simulate rainfall. In this study, performance of super-parameterized community climate system model’s atmospheric only (SPCAM) forced with observed SST and coupled (SPCCSM) versions have been evaluated to capture Indian summer monsoon rainfall characteristics. Analyses show that, simulation of rainfall and its extremes are better represented in the atmospheric model (SPCAM) over the Indian landmass. This is largely because of better representation of convection in the uncoupled version. It is also observed that 2–10 day synoptic mode of the summer monsoon has a large variance over Indian region which may be broadly responsible for extreme events, and SPCAM captures this synoptic variability reasonably well. Our study also indicates that models may have poor moisture holding capacity. This problem is more prominent in SPCCSM.

    • Geo-engineering classiBcation with deterioration assessment of basalt hill cut slopes along NH 66, near Ratnagiri, Maharashtra, India

      ANURAG NIYOGI KRIPAMOY SARKAR ASHOK KUMAR SINGH T N SINGH

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      Western Ghats (WG) in India is endowed with one of the most distinctive and picturesque mountainous landscapes. The region encounters unprecedented rain and non-engineered excavations (especially along highway cut slopes), that turns out to be detrimental to the stability of rock and soil slopes. The present research focuses on accounting the vulnerability condition of rock slopes of differential deterioration intensities along National Highway corridor 66 (NH 66) at Ratnagiri–Sangameshwar (RS) stretch. Rock mass and associated slope stability condition were encapsulated, and studied locations were classified using different geo-engineering classification (GEC) systems such as RMR (Rock Mass Rating), SMR(Slope Mass Rating), CSMR (Continuous Slope Mass Rating), GSI (Geological Strength Index) and RDA (Rock slope Deterioration Assessment). The study introduces a new class in RDA for igneous rocks that are susceptible to high deterioration. Some useful insights have been added and discussed in the light of deterioration-induced block failures which have been integrated with detailed kinematic analysis. The present study recommends that RDA would prove more efficient and informative in the preliminary stage of slope stability investigation for high deterioration susceptible igneous rock masses as compared to other geo-engineering systems.

    • A local magnitude scale $M_{L}$ for the Saurashtra horst: An active intraplate region, Gujarat, India

      VISHWA JOSHI SUMER CHOPRA SANTOSH KUMAR

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      The calibration of local magnitude scale to local tectonics is essential for seismic hazard assessment and quantifying the seismicity in active regions. In the present study, we have developed a local magnitude scale $M_{L}$, for the Saurashtra region, which is a horst, located in the western continental margin of India. The local magnitude scale is developed using 1968 amplitude measurements from horizontal component recordings of 319 earthquakes, obtained from sites in the Saurashtra region, with hypocentral distances ranging from 3 to 298 km. All the 1968 amplitude measurements were inverted simultaneously to determine attenuation curve, magnitudes and station corrections for the studied region. The resultant distance correction term for the Saurashtra is $-log(A_{0}) = 1.31 log(r/100) + 0.0002 (r - 100) + 3$ for 100 km normalization, where $A_{0}$ is the distance correction and $r$ is the hypocentral distance. The distance correction term ($-log A_{0}$) suggests that the attenuation in the Saurashtra region is lower as compared to neighbouring Kachchh region. The station corrections obtained in the present study varies from $-0.31$ to $+0.24$. Overall, standard deviation of the magnitude residuals without station correction is 0.28, while with station correction, it is 0.23, which indicates that applying station correction reduces the variance by 31% and brings the average residual closer to zero.

    • Rajgad GPB: A megaporphyritic flow field, Western Deccan Volcanic Province, India

      PRIYANKA SHANDILYA POUSHALI CHATTERJEE KONDEPUDI PATTABHIRAM MAKARAND BODAS KANCHAN PANDE VIVEK S KALE

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      We describe the distribution and characters of a megaporphyritic basalt flow field that was arguably the earliest described ‘giant phenocryst basalt’ (GPB) from the Deccan Volcanic Province (DVP). It is a marker horizon exposed in a > 30,000 $km^{2}$ area below the Mahabaleshwar Formation in the western DVP. Its presence, distribution and stratigraphic importance as a regional marker horizon are enumerated. Available geochronological and paleomagnetic data suggest that the stratigraphic position of the Rajgad GPB coincides with polarity reversal in Chron 29 recorded from the basaltic lava sequence of the Western DVP.

    • Magnitude estimation of regional earthquakes in India and its adjoining region

      B NARESH PRANTIK MANDAL SOLOMON RAJU R VIJAYA RAGHAVAN G SURESH D SRINAGESH

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      To provide reliable and quick estimation of magnitude for moderate to large earthquakes at regional distances, two magnitude relations specific to the peninsular shield have been proposed based on long-period magnitude ($M_{A}$) and energy magnitude ($M_{E}$), using broadband velocity data of 23 regional events recorded at 18-station seismic network in the state of Telangana and Andhra Pradesh, India. $M_{A}$ is estimated using amplitude of filtered (0.03–0.08 Hz) broadband velocity seismograms, while $M_{E}$ is estimated based on radiated energy using broadband velocity spectra. It is observed that $M_{A}$ for larger events with $M_{w}$ >7.2 saturates, whilst $M_{E}$ does not suffer from saturation even for larger events. Thus, it is apparent that these two magnitude relations can provide magnitude estimates without saturation for all moderate to large regional earthquakes, which, in turn, can provide a homogeneous catalogue for moderate to large regional Indian earthquakes. The data transmission from remote stations to the central server at CSIR-National Geophysical Research Institute (NGRI) is quasi-real-time since it is connected by GPRS and VSAT. Using the proposed region specific magnitude relationships it becomes possible to estimate reliable magnitudes for moderate to large regional Indian earthquakes ($M_{w} \leq 7.2$) within 30 min of the occurrence of an event.

    • Field, petrographic and geochemical characteristics of Sullya alkaline complex in the Cauvery Shear Zone (CSZ), southern India: Implications for petrogenesis

      CHANDAN KUMAR BORAIAHA KUMAR BATUK JOSHI ANDREW C KERR JAYANT KUMAR PADHI SARBARTHA SHANKAR MISHRA RASHMI CHANDAN

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      Significant, but volumetrically smaller, unmetamorphosed and largely undeformed alkaline magmatic suites have been reported from the Southern Granulite Terrain in southern India. These Neoproterozoic alkaline magmatic rocks occur as lenses, dykes and plugs that are mostly within, or proximal to, major shear zones or transcrustal faults. In this contribution, field, petrographic and whole-rock geochemicaldata of Sullya syenites and associated mafic granulites from the Mercara Shear Zone (MSZ), which separates low-grade (greenschist to upper amphibolite facies) Dharwar Craton and high-grade (granulite facies) Southern Granulite Terrain is presented. The isolated body of the Sullya syenite, similar to other alkaline plutons of the Southern Granulite Terrain, shows an intrusive relationship with the host hornblende-biotite gneisses and mafic granulites. The Sullya syenites lack macroscopic foliations and unlike, other plutons, they are not associated with carbonatites and ultrapotassic granites. Potash feldspar and plagioclase dominates the felsic phases in the Sullya syenite and there is negligible quartz. The studied syenites show evidence of melt supported deformation, but show no evidence of recrystallization. Geochemically,they most resemble the Angadimogar syenites (situated 3 km west of the Sullya syenites) with similar major oxide and trace element concentrations. The petrogenetic studies of the Sullya syenite have indicated that they were generated by mixing of two different sources derived from the partial melting of metasomatized continental mantle lithosphere and lower crustal mafic granulites. This melt source could have been emplaced in a rift-related tectonic setting. The emplacement is considered to becontrolled by shears.

    • Upper mantle seismic anisotropy beneath the Kachchh rift zone, Gujarat, India, from shear wave splitting analysis

      BHOOPENDRA SINGH PRANTIK MANDAL

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      Unravelling the anisotropic behaviour of the upper mantle helps to shed light on its present and past deformation processes. In this study, we attempt to explore the seismic anisotropy prevailing within the upper mantle beneath the Kachchh rift zone through shear wave splitting analysis. We have measured the splitting parameters (e.g., fast axis orientation ($\Phi$) and delay time ($\delta t$)) using SKS/SKKS core refracted phases from 112 teleseismic events recorded at NGRI network in the Kachchh region, during 2006–2009 and 2013–2016. The ‘$\Phi$’ and ‘$\delta t$’ estimates vary from $\rm{N}34^{\circ}$ to $\rm{N73^{\circ}E}$ and 0.80 to 1.5 s, respectively. The average vector means of ‘$\Phi$’ and ‘$\delta t$’ for all the stations are found to be $\rm{N(58 \pm 10)^{\circ}E}$ and $(0.99 \pm 0.19)\,\rm{s}$, respectively. Measurements of 59 good SKS/SKKS splitting parameters from 112 earthquakes reveal that the upper mantle is highly anisotropic beneath the Kachchh rift zone with an average fast axis orientation of $\rm{N(58 \pm 10)^{\circ}E}$, which is deviated nearly ($\sim\rm{N18^{\circ}E}$) from the absolute plate motion (APM) direction ($\rm{N40^{\circ}E}$) of the Indian plate in a no-net-rotation reference frame. This deviation of fast axis orientation from APM direction may be attributed to the effect of Kachchh rift zone as well as the presence of structural imprints of the 65 Ma Deccan mantle plume in the study region. And the average delay time of $(0.99 \pm 0.19)\,\rm{s}$ is consistent with the global average (1 s) for continents. Furthermore, the modelled seismic layer thicknesses reveal that anisotropic sources beneath study region are associated with both the lithospheric deformation processes (e.g., 184 Ma African rifting, 88 Ma Madagascar rifting, 65 Ma Deccan mantle plume) as well as asthenospheric flows.

    • Understanding stable isotope systematics of salinity affected groundwater in Mewat, Haryana, India

      GOPAL KRISHAN N C GHOSH C P KUMAR LALIT MOHAN SHARMA BRIJESH YADAV M L KANSAL SURJEET SINGH S K VERMA GOKUL PRASAD

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      Mewat district in Haryana located in the semi-arid region of India has been reported continual increase of groundwater salinity. Stable isotopes, $\delta^{18}\rm{O}$ and $\delta\rm{D}$, of groundwater and rain water were successfully used for characterization and source identification of salinity affected groundwater in the area. Eleven representative groundwater samples were of the pre-monsoon (May), monsoon (August) and post-monsoon (November) seasons were analyzed for determining $\rm{EC}$, $\delta^{18}\rm{O}$, $\delta D$ and other parameters. The mean EC of the samples was determined $6712 \mu\rm{S/cm}$ for the pre-monsoon, $4743 \mu\rm{S/cm}$ for the monsoon and $6602 \mu\rm{S/cm}$ for the post-monsoon. The slope of LMWL (8.13) obtained from the bivariate plot showed a very close to the GMWL (8) and the slope of rain water (7.47) and groundwater samples found lied on the right of the LMWL for all the seasons. Slopes observed for the pre-monsoon (6.76), monsoon (5.63) and postmonsoon (6.11) seasons indicated some evaporative enrichment of water before the groundwater recharge. The increase of $d$-excess values from 0.74 in pre-monsoon to 3.75 in monsoon and 4.46 in post-monsoon seasons suggested modern recharge with low evaporation. The recharge by meteoric water was noted from the decrease in the mean value of EC in the monsoon season and its increase in the post-monsoon season, which suggested possible ‘mechanism of mixing’. All these processes qualitatively predicted the recharge and discharge locations in the study area.

    • Evolution of Late Cretaceous to Palaeogene basalt–andesite–dacite–rhyolite volcanic suites along the northern margin of the Ladakh magmatic arc, NW Himalaya, India

      NONGMAITHEM LAKHAN A KRISHNAKANTA SINGH B P SINGH KSHETRIMAYUM PREMI GOVIND OINAM

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      This paper describes a comprehensive geochemical study of basalt–andesite–dacite–rhyolite volcanic association in the Khardung volcanic suite along the northern margin of the Ladakh magmatic arc. This volcanic association is outcropped mainly in the segment of the further north of the Khardung village to Khalsar delineating from the Ladakh magmatic arc by $\sim$2 km thick porphyritic sill. The closed association of basalt–andesite–dacite–rhyolite volcanic within a volcanic suite suggests that these rocks may be genetically inter-related and might have derived from the same parental magma source. Felsic lavas (dacite–rhyolite) show $\rm{SiO}_{2}$ range from 64.75 to 79.11 wt.%, while intermediate lavas (basaltic andesite–andesite) ranges from 50.80 to 51.81 wt.% with mafic lavas (basalt) span from 53.39 to 62.05 wt.%. These volcanic suites show enrichment in LIL elements (Rb, Ba, Th, U, and Pb) and depletion in Nb, P, and Ti, which can be evident in spider diagrams with pronounced to mild Eu negative anomalies in REE patterns. Previous reports on zircon U–Pb ages of the Khardung volcanics range between 60 and 69.7 Ma confirm an upper bound eruption age of this volcanic suite as pre-collision continental arc magmas. Hence, the results of geochemical modelling suggest that the Khardung mafic–intermediate-felsic lavas were generated from the melting of 1–4% spinel and garnet-bearing lherzolite sources. The generated parental magmas were modified by crustal materials during the magma ascent along with fractional crystallization and were metasomatized by slab-derived fluids released from the subducting Neo-Tethyan oceanic crust during the Late Cretaceous to Palaeogene in the northern margin of the Ladakh magmatic arc.

    • A revisit to the regulation of oxygen minimum zone in the Bay of Bengal

      B SRIDEVI V V S S SARMA

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      Occurrence of intense oxygen minimum zone (OMZ) is known in the Bay of Bengal (BoB), but it has been recently reported to have become more acute and is at its tipping point. Here, we show that the intensification of OMZ to acute condition is a random and short-term rather than perennial phenomenon based on re-evaluation of old and recent information in the BoB. Short-term modifications in dissolved oxygen (DO) in the OMZ are caused by balance among physical forcings: salinity stratification, occurrence of cyclonic (CE), and anticyclonic eddies (ACE). Our analysis reveals that ‘acute OMZ’ is only a transient phenomenon in the Bay since the dynamic periodic physical forcings, particularly ACEs, do not allow it to become a dead zone.

    • Observed variability of the East India Coastal Current on the continental shelf during 2010–2018

      S MUKHOPADHYAY D SHANKAR S G APARNA V FERNANDO A KANKONKAR

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      We describe the variability of the East India Coastal Current (EICC) during 2010–2018 on the outer continental shelf using data from four ADCP (acoustic Doppler current profilers) moorings deployed off Gopalpur ($\sim19.5^{\circ}\rm{N}$), Visakhapatnam ($\sim18^{\circ}\rm{N}$), Kakinada ($\sim16^{\circ}\rm{N}$), and Cuddalore ($\sim12^{\circ}\rm{N}$) on the east coast of India. In general, the shelf EICC mirrors the slope EICC for the annual and semi-annual cycles, but the shelf-slope coherence is weaker and patchy for the 120-day and intraseasonal bands. The seasonal cycle, which consists of the annual, semi-annual, and 120-day bands, dominates the observed variability. The amplitude of the annual cycle varies over the time series. In the intra-annual band, variability tends to switch between the semi-annual and 120-day bands, but the former dominates throughout the time series off Cuddalore, the southernmost location. The EICC appears as a shallow current in all period bands, including the seasonal cycle, off Cuddalore, but even the intraseasonal EICC appears as a deep current at the other three locations. A wavelet analysis shows seasonal variation of the wavelet power in the intraseasonal band, suggesting that the amplitude of intraseasonal variability itself varies with season, but there is no clear seasonal pattern. As on the continental slope, the annual and semi-annual components are coherent along the coast, but alongshore coherence is weak at shorter time scales. Upward phase propagation is evident for the seasonal cycle at all locations, but downward phase propagation, seen on the slope off Cuddalore, is evident on the shelf as well. The 500-day low-pass filtered shelf EICC is not weak and the sub-annual variability is comparable to that on the slope. The long ADCP record allows us to confirm the dominance of seasonality in the EICC regime in a robust fashion; the data show that the EICC tends to flow in its canonical poleward (equatorward) direction during spring (winter). This dominance of seasonality enhances the predictability of the EICC.

    • Mini-RF S-band observation of Ohm and Stevinus craters using circular polarization ratio and m-chi decomposition techniques

      ASHKA D THAKER SHREEKUMARI M PATEL PARAS M SOLANKI

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      The aim of the study was to observe two lunar impact craters of Copernican age, Ohm ($\rm{18.4^{\circ}N, 113.5^{\circ}W}$) and Stevinus ($\rm{32.5^{\circ}S, 54.2^{\circ}E}$) under microwave radar data of Miniature Radio Frequency (Mini-RF), an instrument onboard Lunar Reconnaissance Orbiter (LRO) of NASA, where Ohm is located on the far side of the Moon and Stevinus is situated on the near side of the Moon. We have analyzed the characters of impact ejecta melt of both the craters in radar data which are not evidently distinguished in the high resolution optical data of narrow angle camera (NAC) and wide angle camera (WAC) of LRO mission. Circular polarization ratio (CPR) and m-chi decomposition images were developed using ENVI and ArcGIS software which were used to understand surface roughness and backscattering properties of Ohm and Stevinus craters. Both the craters evidently have high CPR values indicating either exposure of fresh material or elevated surface roughness due to surface geometry. The m-chi decomposition of Ohm and Stevinus craters shows dominant yellowish hue suggesting a backscatter combination of double-bounce (db) scattering and volume scattering (vs) in contrast to the surrounding terrain which shows Bragg scattering (bs) according to the 7-fold classification colour-wheel. Using available optical and Mini-RF data geological maps of both the craters were generated including features such as boundary of ejecta blanket, ejecta boulders and mass wasting in the crater.

    • Study of mixing ratios of $\rm{SO}_{2}$ in a tropical rural environment in south India

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      Sulphur dioxide is a toxic pollutant in the atmosphere emitted from natural sources and human activities. Normally, $\rm{SO}_{2}$ has a life-time of about 2 days in the atmosphere and is not transported to long distances from its source region. However, under favourable circumstances such as low humidity or high wind speed, it can travel intercontinental distances from the point of emission. In this article, we have analysed the surface mixing-ratio of $\rm{SO}_{2}$ measured over the time period from January 2010 to April 2012 at a rural region in south India. It is found that $\rm{SO}_{2}$ mixing-ratio is very low over this region with an annual mean value in the range of 0.21–0.24 ppbv. OMI satellite estimates an annual mean value of 0.5 Dobson Units (DU) over the same location and period. However, during January to May relatively higher concentrations of $\rm{SO}_{2}$ are observed, mainly coming from power plants located in southern and eastern India as indicated by higher $\rm{SO_{2}/NO_{2}}$ ratios of greater than 0.5. In one instance, on June 20th, 2011, it is found that the OMI $\rm{SO}_{2}$ value was a factor of 13 higher than 2011 annual mean at Gadanki. Using the FLEXible PARTicle dispersion model (FLEXPART) and satellite data, it is found that the observed higher $\rm{SO}_{2}$ value on 20th June was due to intercontinental transport of $\rm{SO}_{2}$ from Nabro volcanic eruption. Using the FLEXPART model with ECLIPSE-v5 emission inventory, the observed seasonal variation of $\rm{SO}_{2}$ could be well reproduced; however, the mixing ratios are found to be overestimated. CAMS (Copernicus Atmosphere Monitoring Service) $\rm{SO}_{2}$ reanalysis values available through its implementation in the ECMWF Integrated Forecasting System are a factor of 7.8 higher than observations, possibly due to incorrect vertical profile used in the model.

    • Geochemical characteristics of the Late Cretaceous radiolarian cherts from North Andaman Island, Bay of Bengal, India

      S H JAFRI D SRINIVASA SARMA TAVHEED KHAN D K SINGH

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      The radiolarian cherts of Late Cretaceous age are reported in the Andaman-Nicobar ophiolites of Bay of Bengal, India. They are of chocolate-coloured (Type-I) and light pink-coloured (Type-II) varieties, juxtaposed and tectonically associated with phyllites, claystones and basalts and are exposed in eastern part of North Andaman Island. These cherts are composed of radiolarian tests in a fine-grained ferruginous matrix.Type-I radiolarian cherts have low $\rm{SiO}_{2}$, and high $\rm{Al_{2}O_{3}}$, $\rm{Fe_{2}O_{3}^{(T)}}$, $\rm{MgO}$, $\rm{Na_{2}O}$ and $\rm{TiO_{2}}$ and trace elements as compared to Type-II cherts. $\rm{Al–Fe–(\Sigma REE–Ce)}$ diagram of the studied cherts indicates a mixed terrigenous and volcanogenic source. $\rm{La_{N}/Ce_{N}}$ ratios (0.76–0.89 for Type-I and 0.71–0.88 for Type-II) and Ce-anomalies $\rm{(Ce/Ce^{\ast} = 1.15–1.33}$ for Type-I and 1.07–1.38 for Type-II) and other elemental ratios in these cherts suggest that they were deposited in continental margin environments. It has been suggested that the studied samples of cherts were deposited at different places, were scrapped off the subducting plate, became tectonically juxtaposed. They were obducted onto the leading edge of the Eurasian continent during the Late Cretaceous prior to the currently active Andaman–Java subduction, that was probably initiated during the Late Miocene.

    • Very low frequency electromagnetic (VLF-EM) study over Wajrakarur kimberlite Pipe 6 in Eastern Dharwar Craton, India

      SARVESH KUMAR SANJIT KUMAR PAL ARINDAM GUHA

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      The Wajrakarur kimberlite Pipe 6 in Eastern Dharwar Craton, is hardly explored using latest ground-based geophysical techniques. The present study uses the Very Low Frequency Electromagnetic (VLF-EM) method for understanding the aerial extension, depth and geometry of the kimberlite pipe. The VLF-EM data have been analyzed using Fraser filtering of in-phase component, 3D Euler deconvolution of Fraser filtered in-phase data, radially average power spectrum (RAPS) of VLF data (raw data) and 2D inversion of VLF data (raw data). The Fraser filtered in-phase grid anomaly map has witnessed as an effective tool for mapping extension of the kimberlite pipe. The maxima of Fraser filtered in-phase component has been observed as a key parameter to delineate the conducting bodies.The high apparent current density in Karous–Hjelt (K–H) pseudo section locate relatively conducting body possibly associated with kimberlite pipe. Two depth interfaces at about 15 and 32 m have been delineated using RAPS. 3D Euler solution indicate dyke-like structure associated with kimberlite pipe having depth solutions ranging from 6 to 40 m with mode of depth 17 m in the study area. 2D resistivity sections indicate that causative bodies are in the depth range of 15–50 m. The results of VLF-EM study are well validated using geological borehole data over the study area reported by Geological Survey of India.

    • An integrated approach for the identification of lithofacies and clay mineralogy through Neuro-Fuzzy, cross plot, and statistical analyses, from well log data

      MUHSAN EHSAN HANMING GU

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      Today, researchers face multiple challenges identifying clay mineral types and lithofacies from well log data. This research paper hopes to offer new insight into this particular challenge. Formation evaluation characteristics play a significant role in the exploration and production of future and current oil and gas fields. The proposed methodology in this study uses an integrated approach that includes: (1) numerical equations, (2) Neuro-Fuzzy neural networks, (3) cross plots, and (4) statistical analyses. This proposedintegrated approach is capable of dramatically improving the accuracy of the results. Well logging data provide valuable information for identifying lithofacies, clay mineralogy types, as well as other important hydrocarbon reservoir characteristics. Talhar Shale in the Southern Lower Indus Basin, Pakistan, is composed of interbedded shale, sand, and shaly-sand, intervals that have been identified via the lithological interpretation process of well logs. Talhar Shale contains montmorillonite type clay with minor amounts of illite, glauconite, and various micas that can be easily identified by natural gamma rayabsorption profiles, as well as through ratio logs, bulk density log, and photoelectric absorption index log. These interpretations can be further confirmed via cross plots and other statistical analyses. This approach consists of a comprehensive study of well logging data and thus can lend itself to be a helpful component in characterizing the hydrocarbon structures of the Talhar Shale.

    • Modelling, evaluation and simulation of drought in Iran, southwest Asia

      BEHROUZ SOBHANI VAHID SAFARIAN ZENGIR MOHAMAD HASAN YAZDANI

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      The drought phenomenon is not specific to a region and it affects different parts of the world. One of these areas is Iran in southwest Asia, which suffered from this phenomenon in recent years. The purpose of this study is to model, analyze and predict the drought in Iran. To do this, climatic parameters (precipitation, temperature, sunshine, minimum relative humidity and wind speed) were used at 30 stations for a period of 29 years (1990–2018). For modelling of the Combined Indicateurs based on four indices, StandardizedEvapotranspiration Torrent White Index (SET), Standardized Precipitation Index (SPI), Standardized Evapotranspiration Blanney Creedal FAO Index (SEB) and Modified CZI Index (MCZI) were fuzzy in Matlab software. Then the indices were compared and the Topsis model was used for prioritizing areas involved with drought. Finally, Anfis adaptive artificial neural network model was used to predict. Results showed that the new fuzzy index TIBI for classifying drought reflected above four indicators with high accuracy. Of these five climatic parameters: (precipitation, temperature, sunshine, minimum relative humidity and wind speed) used in this study, the temperature and precipitation parameters had the mosteffect on the fluctuation of drought severity. The severity of the drought was more based on 6-month scale modelling than 12 months. The highest percentage of drought occurrence was at Bandar Abbas station with a value of 24.30 on a 12-month scale and the lowest was in Shahrekord station with a percentage of 0.36% on a 6-month scale. Based on Anfis model and TIBI fuzzy index, Bandar Abbas, Bushehr and Zahedan stations were more exposed to drought due to the TIBI index of 0.62, 0.96 and 0.97, respectively. According to the results in both 6 and 12 months scale, the southern regions of Iran were more severelyaffected by drought, which requires suitable water management in these areas.

    • Cohesive river bank erosion mechanism under wave-current interaction: A flume study

      VIKAS KUMAR DAS SAYAHNYA ROY KRISHNENDU BARMAN SUSANTA CHAUDHURI KOUSTUV DEBNATH

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      The effect of hydrodynamic forces due to combined action of surface waves and current on the riverbank is critical to understand sediment entrainment, transport and bank line retreatment process. In understanding the temporal effect of turbulent structures under induced wave-current Cow, a series of laboratory experiments were carried out. Micro-Acoustic Doppler Velocimeter (ADV) and Ultrasonic Ranging System (URS) were used simultaneously for the measurement of velocity fluctuations and bank undercut depth increment. Modulation of the turbulent flow characteristics and the benefaction of turbulent bursting structures at the initiation of erosion process and before the failure of the cohesive bank due to undercut progression are discussed. The results show that velocity and Reynolds shear stress have direct dependence on the size and rate of the entrainment of cohesive aggregates from bank face. The effect of wave-current motion leads to an increase in shear stress at the lateral bank giving rise to erosion and transportation of sediment particles/aggregates. Quadrant analysis of the random velocity fluctuation under wave-current flow at the initiation of erosion process shows strong presence of ejection and sweep events. Findings from the present study may provide a better understanding on the design of cohesive bank erosion control measures.

    • Interpretation of stratigraphy and structure of the Neoarchaean Dharwar Supergroup of rocks in Chitradurga area, Dharwar Craton

      ABHINABA ROY H M RAMACHANDRA SILADITYA SENGUPTA

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      The Neoarchaean Dharwar Supergroup of rocks in the Chitradurga area unconformably overlie the Mesoarchaean Peninsular Gneissic Complex in the west and are tectonically juxtaposed with Javagondanahalli Schist Belt in the east. The rocks of the supergroup have been divided into older Bababudan and younger Chitradurga Groups. We support the recent division of the Bababudan rocks into a lower conglomerate–sandstone facies association and an upper sandstone–mudstone facies association indicating tidal flat depositional environment. The Talya Conglomerate sequence at the base of the Chitradurga Group is inferred to represent a fault-controlled debris flow deposit. The basin opens out to the east where sedimentation and volcanism took place on an uneven basement surface. The Vanivilas and Ingaldhal Formations likely represent contemporaneous and overlapping sequences indicative of facies variation in space. The KM Kere Conglomerate at the base of the Hiriyur Formation represents a facies series comprising a sequence of volcanic–pyroclastic–volcaniclastic–epiclast association. We propose a four-fold stratigraphic classification with introduction of a new ‘Kantaramanahalli Formation’, placed above the Vanivilas and Ingaldhal Formations and below the Hiriyur Formation. The interpretation of multiple deformed nature of Dharwar Supergroup of rocks and the dominance of the second deformation ($D_{2}$) is supported. The initial irregularities on basement surface and the $F_{1}$ folds have significant role in fold superposition and outcrop patterns. The intra- and interformational ductile shear zones have dominant sinistral transcurrent component. Structural studies are conclusive of simple shear ($D_{2b}$ ) superposed on intense pure shear ($D_{2a}$) indicative of an overall transpressional type of horizontal tectonics.

    • Assessing rainfall erosivity and erosivity density over a western Himalayan catchment, India

      JAGDEEP SINGH OMVIR SINGH

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      The present study aims to assess rainfall erosivity and erosivty density both in space and time over the Suketi River catchment of western Himalayan region in India during 1971–2015. The data used comprises of daily rainfall measurements at three rain gauge stations, which are sparsely distributed over the catchment. Rainfall erosivity was assessed by employing Wischmeier and Smith algorithms, whereas erosivity density was estimated by applying Kinnell’s algorithm. The spatial distribution of both algorithms was analyzed through Kriging method based on geographical information system. The obtained results indicate remarkable year-to-year, seasonal and monthly variations in average annual rainfall erosivity and erosivity density. Apart from this, individual cases of high and very high rainfall erosivity and erosivity density were noticed. The long-term average annual rainfall erosivity and erosivity densityrevealed a general decreasing trend. This decreasing trend in rainfall erosivity was found to be statistically significant at 0.05 significance level, whereas it was found to be non-significant for erosivity density. The highest values of both indices were observed in the month of July followed by August and June particularly in northern parts. These results indicate that July month followed by August and June arethe most susceptible months for soil erosion over the Suketi River catchment with lower reaches (northern) being the most vulnerable one. Finally, results of this study will be valuable for farmers, agronomists and regional planners in chalking out best management practices for reducing water erosion in vulnerable areas of the catchment.

    • Substantiation of Reunion plume induced prolonged magmatic pulses (ca. 70.5–65.5 Ma) of the Deccan LIP in the Chhotanagpur Gneissic Complex, eastern India: Constraints from $^{40}\rm{Ar}/^{39}\rm{Ar}$ geochronology

      RAJESH K SRIVASTAVA FEI WANG WENBEI SHI

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      This study presents $^{40}\rm{Ar}/^{39}\rm{Ar}$ geochronology on the mafic dykes emplaced in the Damodar valley Gondwana sedimentary basins of the Chhotanagpur Gneissic Complex (CGC) to authenticate prolonged mafic magmatic activities during Maastrichtian period. A couple of earlier and one new $^{40}\rm{Ar}/^{39}\rm{Ar}$ plateau ages, which range in age from ca. 70.5 to 65.5 Ma, suggest prolonged ($\sim$5 myr) magmatic activities in the CGC. These syn- and pre-Deccan LIP magmatic intrusive activities in the CGC are supposedly related to the Reunion mantle plume. The reported age of 70.5 $\pm$ 0.9 Ma of a NE-trending mafic dyke emplaced within the Raniganj basin could probably be the earliest record of the Reunion mantle plume activity in the Indian shield. A number of other early magmatic rocks, related to the Reunion mantle plume induced Deccan LIP event, are also recorded elsewhere in the Indian shield and supportive of prolonged magmatic activities. Finally, this study also provides a better constraint on the initiation and lateral extent of the Reunion mantle plume induced Deccan LIP.

    • Trend analysis of weather extremes across the coastal and non-coastal areas (case study: Turkey)

      MOHSEN ABBASNIA HUSEYIN TOROS

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      High-quality daily climate parameters were prepared from 71 stations across Turkey for assessment of the long-term changes in weather extremes from 1961 to 2016. Results of temperature extremes showed that warm extremes had more significant trends than those found in cold extremes. Moreover, the growing season length revealed significant negative trend recorded at local scale for all coastal stations. The results of the precipitation extremes revealed decreasing trends in the number of precipitation days and the volume of precipitation. Only, a small percentage of stations experienced significant increasing trends for the average of total precipitation and very wet days, especially over the southeast coast of Black Sea. Strong evidence for shorter periods of warming and shorter length of growing seasons, alongside a lesser number of heavy rainfalls in the lowland region of coastal stations, are spatially more coherent for extreme events than in the highlands and inland stations. Prolonged periods of high temperatures increased for some of the coastal regions in Turkey over the last 50 yrs. Overall, the temperature extremes are expected to change in favour of warm and short-lasting events, while the precipitation extremes are expected to change towards a shorter duration and a higher intensity of rainfalls. Hence, higher content of atmospheric humidity over coastal locations is expected to cause stronger rainfalls, especially for higher latitudes.

    • An integrated approach of GIS, RUSLE and AHP to model soil erosion in West Kameng watershed, Arunachal Pradesh

      BISWAJIT DAS REETASHREE BORDOLOI LOBSANG TASHI THUNGON ASHISH PAUL PANKAJ K PANDEY MADHUSUDHAN MISHRA OM PRAKASH TRIPATHI

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      Soil erosion has always been a major environmental problem in many parts of the world including the northeastern region of India. An increase in the rate of soil erosion has tremendous implications on land degradation, biodiversity loss, productivity, etc. Hence, assessment of soil erosion hazard and its spatial distribution is essential to serve as a baseline data for effective control measures. The present study uses revised universal soil loss equation (RUSLE) and analytical hierarchy process (AHP) approach integrated with geospatial technology for modeling soil erosion hazard zone of West Kameng watershed of Arunachal Pradesh, Northeast India. The assessment showed that the erodibility factor of soil ranged between 0 and 0.38 t/ha/MJ/mm and slope length and steepness factor increases with increase in slope angle. Lower normalized difference vegetation index (NDVI) values depict vegetation cover and higher values represent the rocky area or barren land. Spatial distribution of conservation support practice on soil loss indicated the variability (0–1) where lower value represents the higher conservation practice.The predicted average soil erosion rate was 124.21 t/ha/Yr. Normalized eigen vector values ranged between 0.03 and 0.20. The areas with more slope, relative relief, drainage density, lineament density, and frequency have shown comparatively higher eigen vector values, and it has been noticed that the strength of these eigen vectors reduces with a decrease in the values of the parameters. The spatial soil erosion potential map was delineated using eight geo-environmental variables (LULC, geomorphology, slope, relative relief, drainage density, drainage frequency, lineament density, and lineament frequency). The soil hazard map showed that the moderate soil erosion has the maximum(57.71%) area cover followed by high erosion class (26.09%)which depicts that most of the watershed areas are moderate to high vulnerable to soil erosion. The efficiency of the AHP was validated applying area under curve (AUC) method which result 84.90% accuracy in the present study. Based on the findings, it is being recommended that present watershed requires adequate control procedures on a priority basis to conserve soil resources and reduce flood events and siltation of water bodies.

    • Iron limitation study in the North Indian Ocean using model simulations

      M K SHARADA C KALYANI DEVASENA P S SWATHI

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      There have been many studies on iron as a limiting nutrient for productivity in the World Ocean, but only a few studies have been done in the Arabian Sea on iron limitation. Sensitivity of primary productivity, chlorophyll, nitrate, $\rm{pCO_{2}}$ and carbon flux in the Arabian Sea to one of the parameters related to iron limitation has been investigated using a three-dimensional coupled biogeochemical model (TOPAZ) embedded in Modular Ocean Model (MOM) in the global domain, for climatology and interannual variability. Initially, the model results are evaluated for many of the biogeochemical components using data from World Ocean Atlas, satellites and cruises in the Arabian Sea. It is noticed that model results capture spatial and temporal variations of some of the biogeochemical components and fluxes in the north Indian Ocean. Subsequently, it is shown that micronutrient iron plays a significant role on the growth of phytoplankton, utilization of nutrients, $\rm{pCO_{2}}$ in the ocean and carbon flux across the air–sea interface in north and north-west regions of the Arabian Sea.

    • Gravity–magnetic appraisal at the interface of Cuddapah Basin and Nellore Schist Belt (NSB) for shallow crustal architecture and tectonic settings

      SHUVA SHANKHA GANGULI SANJIT KUMAR PAL J V RAMA RAO B SUNDER RAJ

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      Cuddapah Basin (CB) is an intracontinental, Proterozoic basin Canked by Eastern Dharwar Craton(EDC) in the west, Nellore Schist Belt (NSB) and Eastern Ghat Mobile Belt (EGMB) in the east,represents second largest Proterozoic basin of India. Gravity and magnetic surveys were carried out at the interface of Cuddapah Basin (CB) and Nellore Schist Belt (NSB) covering $\sim 2880 \rm{km}^{2}$ area. Gravity map has brought out some distinct zones. The thrusted contact of NSB and Cuddapah sediments has been well delineated from the gravity map by NE–SW trending steep gradient of contours. Relatively high gravity values are observed over NSB in the southeastern part, moderately high values are observed over Cumbum Formation, but distinct low is observed over Baironkonda Formation. These gravity highs and lows are mainly the manifestation of basement characteristics and intrusives. The magnetic map shows two distinct domains, viz., moderate to low zone in the southern part, and moderate to high zone in the northern part. Regional gravity map suggests a change in basement characteristics from felsic to mafic from NW to SE. Presence of mafic basement may be representing EGMB group of rocks underneath the Cuddapah sediments at the eastern part of the study area. The joint gravity and magnetic modelling reveal varied nature of sedimentary units in terms of density and susceptibility and change in basement characteristic.

    • Assessing the emissions of $\rm{CO}$, $\rm{SO}_{2}$, and $\rm{NO_{X}}$ and predicting potential zones of $\rm{CO}$ concentration from sugarcane factories in Egypt

      MOHAMED ABDELKAREEM YAO TAN RAAFAT M EL ATTAR ABDELMONSEF HASSAN

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      Air pollution causes significant environmental and health problems around the world. The present study assesses the emission of $\rm{CO}$, $\rm{SO}_{2}$, and $\rm{NO_{X}}$ from six sugarcane factories (SCFs) in Egypt, which are using two dominant fuels, bagasse and natural gas. The detected CO emission and concentrations levels from the stacks of SCFs that used bagasse were higher ($\rm{1751–3030 mg/Nm^{3}}$) than those using a mixture of bagasse and natural gas ($\rm{555 mg/Nm^{3}}$), as well as natural gas only ($\rm{169.2–246.5 mg/Nm^{3}}$). The emission of CO is higher than permissible levels, but $\rm{SO_{2} (2.5–26.5 mg/Nm^{3}})$ and $\rm{NO_{X} (25.5–149.75 mg/Nm^{3}})$ emissions in all kinds of fuels are within the permissible levels. Dispersion of CO in the ambient from stack emission from Kom Ombo SCF is simulated using the Ministry of Economic, Trade, and Industry Low-Rise Industrial Source dispersion (METI-LIS) model. The results predicted the higher risk zone (>10 ppmv) extends $\sim$1 km around the KSCF and occupies the near middle part of the plume, but the lower zone (<0.1 ppmv) occupies the outer zone and extends for several kilometers. Measurements in the ambient air validated the predicted model, which revealed that people living in areas about 1 km south and west downwind of the KSCF are exposed to higher levels of CO concentration. Usage of bagasse in SCFs needs to be replaced by natural gas for the reduction in emission of pollutants. Moreover, pollutants emitted from the SCFs should be monitored periodically to control the emission for healthy environment.

    • Delineation of shallow structures in Madawara igneous complex, Bundelkhand Craton, India using gravity–magnetic data: Implication to tectonic evolution and mineralization

      ANIMESH MANDAL ATHUL CHANDROTH AUROBINDO KUMAR BASANTARAY

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      An integrated gravity–magnetic study has been carried out over Madawara Igneous Complex (MIC) in southern part of Bundelkhand Craton with an aim to decipher shallow crustal configuration and mineralized zones, thereby to improve the understanding of tectonic evolution of the region. Derived gravity and magnetic anomaly maps show good correlation with known geology and have delineated continuity of mafic–ultramafic intrusive bodies in EW direction. Radially averaged power spectrum (2D) and solutions derived from 3D Euler deconvolution have revealed average basement depths for gravity sources as $\sim 0.3, 1.2$ and $3.2 k$, whereas for magnetic sources as $\sim 0.3$ and $1.2 \rm{km}$. From this study, these interfaces could be attributed to sedimentary origin for shallowest layer, mafic–ultramafic intrusive for intermediate layer and changes within the granite–gneissic basement for deeper solutions. Two-dimensional inverse modelling of residual gravity anomaly has delineated intrusion of highly dense mafic–ultramafic rocks from deeper part within the granite gneissic complex. Deeper basement from gravity and shallower from magnetic data indicate presence of two-stage magmatism within a subduction setting where the second magmatic emplacement probably occurred with a magma that comprises high magnetic material. High gravity and magnetic anomalies are observed over the mafic and ultramafic rock samples which are already identified (based on previous geochemical studies) as prospective zones for Cr, Ni and PGE mineralization. Thus, it can be inferred from this study that the mafic–ultramafic intrusive bodies are favourable targets for Cr–Ni–PGE mineralisation which may be obtained between a depth range of around 300 m to 3 km. Thus, the study enhances the scope for further integrated geophysical investigation over the identified prospective zones as well as provides important clues on magmatic evolution of the region.

    • Physico-chemical conditions of crystallization and composition of source magma of the Grenvillian post-collisional mafic–ultramafic rocks in the Chhotanagpur Gneissic Complex, Eastern India

      SUSMITA DAS BAPI GOSWAMI CHITTARANJAN BHATTACHARYYA

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      In the Chhotanagpur Gneissic Complex (CGC) of Eastern India a suite of mafic and ultramafic rocksoccurs as sills, dykes and enclaves within porphyritic granitoid pluton. These mafic and ultramafic rocks and host porphyritic granitoids were emplaced in a post-collisional setting around $998 \pm 10 \rm{Ma}$ ago. Field occurrence, petrology and mineral chemistry of the mafic–ultramafic rocks have been studied. Both the mafic $\rm{(Pl + Hyp + Di + Hbl + Bt + Mag + Spn \pm Ol \pm Spl)}$ and ultramafic rocks $\rm{(Di + Hyp + Bt \pm Hbl \pm Ol \pm Pl \pm Spl \pm Ep \pm Spn)}$ are composed of same minerals but in different modal proportions. Plagioclase, clinopyroxene, orthopyroxene, amphibole, biotite and rarely olivine and spinel are important primary minerals of mafic–ultramafic suite. Primary amphiboles, biotites and pyroxenes show their affinity with shoshonitic lamprophyres. Chemically these rocks are similar to the kentallenite (of appinite suite) and are enriched in both compatible (Fe, Mg, Ni, and Cr) and incompatible (K, Ba, Rb, and LREE) elements and show crust-like trace element patterns. Crystallization of clinopyroxene before labradorite and presence of primary hornblende and biotite suggest high water content while biotite–magnetite–sphene assemblage suggests high $f\rm{O}_{2}$ of the magma. Liquidus temperature $(975–1088^{0}\rm{C})$ of the parental magma of the mafic–ultramafic rocks was obtained by two-pyroxene thermometer. The pressure (2.9–5.7 kbar) and near-solidus temperature $(782–819^{0}\rm{C})$ of crystallization were determined using the amphibole–plagioclase geothermobarometry. Similar range of values of pressure, temperature and $f\rm{O}_{2}$ values were obtained using other thermobarometers. High $\rm{H_{2}O}$ and $f\rm{O}_{2}$ (>NNO buffer) of the magma are characteristics of convergent setting. The mafic–ultramafic rocks of the suite probably crystallized from a magma which had high $\rm{SiO_{2}}$ (48.16–67.64 wt%), high $\rm{CaO}$ (3.01–11.73 wt%), high $\rm{K_{2}O}$ (1.34–4.49 wt%) and low $\rm{TiO_{2}}$ (0.04–2.71 wt%) contents and intermediate Mg# (46.73 and 59.78).

    • Petrology, geochemistry and geochronology of Neoarchean A-type granite from Alwar Basin, North Delhi Terrane, NW India

      ARINDAM MISRA ALOK CHAUHAN DEBAPRIYA CHATTERJEE

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      A 2.53 Ga old Jhiri granite has been dated using zircon U–Pb systematics from the lowermost succession of North Delhi Terrane (NDT). The granite is an intrusive into the rocks of meta-volcano sedimentary sequence of basal Raialo Group of the Delhi Supergroup. Geochemically, the pluton is peraluminous, magnesian, alkali-calcic to alkali in character with strong negative anomaly for Ba, Ta, P and Ti and positive anomaly for K, Pb and Th. The plots on tectonic discrimination diagrams show the Jhiri granite to be of A-type with an affnity to the volcanic arc related granitoids. The comparison of Jhiri pluton with other Neoarchean granitoids of the Aravalli Delhi Mobile Belt (ADMB) and Bundelkhand craton shows the granite to be more evolved and have strong depletions for HREEs with $\rm{(La/Yb)_{N}}$ > 20. A hybrid source, having component of fractional crystallization-derived mafic melt mixing with melt generated by partial melting of early formed felsic crust in a back-arc extension or post-orogenic extension setting is proposed as the possible scenario for the generation and emplacement of Jhiri pluton.

    • Soft-sediment deformation structures in a Permo-carboniferous glacio-marine setting, Talchir Formation, Dudhi Nala, India

      H N BHATTACHARYA AMRITA MUKHERJEE

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      The Permo-carboniferous glacio-marine Talchir Formation of Dudhi Nala, West Bokaro Coal Basin, India, hosts soft-sediment deformation structures that originated from liquefaction and concomitant fluidization of unconsolidated sediments at or close to the sediment–water interface. Since liquefaction of water saturated sediments may be initiated by different endogenic or exogenic triggering agents, identification of the trigger needs careful analysis of the deformation structure, as well as depositional mechanism and environment of deposition of the host sediments. In-depth analysis of the studied liquefaction- and fluidization-induced soft-sediment deformation structures and sedimentary attributes of the host sediments of the studied succession unequivocally stand against the role of strong wave and tidal action, rapid sediment loading, mass-flow and subaqueous slides related shear stress, and water or gas seepage as the triggering agent. However, development of the soft-sediment deformation structures, close to sediment–water interface, closeness to syn-sedimentary fault, flowage along the tilt towards the fault, confinement within undeformed beds, episodic character and close similarities with structures that are formed during recent earthquakes, are consistent with seismic triggering for liquefaction. The studied shallow marine sediments record a sequel of climatic amelioration, glacial retreat, shallow marine sedimentation, glacio-isostatic rebound and related syn-sedimentary faulting and development of soft-sediment deformation structures.

    • Tectonic evolution of Kutch sedimentary basin, western India

      K CHANDRA MOULI P CHANDRASEKHAR D P RAO V K DADHWAL

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      Lithological variations, circular spectral anomalies, geological structures such as folds, faults, lineaments and shear zones of Kutch sedimentary basin were interpreted using IRS-LISS III satellite data. Aeromagnetic data was also interpreted qualitatively and quantitatively and a number of anomalous magnetic zones, faults, lineaments and domal structures were mapped. Magnetic basement depths and thickness of sediments were also computed. A number of alternate basement ridges/highs/uplifted blocks and depressions/lows/downthrown blocks were delineated. The information obtained from satellite remote sensing and aeromagnetic data were then integrated and the results were compared with published literature on gravity, magnetic (ground), magnetotelluric and seismic data, and also with field geology and well data. Structural controls in spatial domain (latitude, longitude and depth) were derived by establishing spatial relationship among different geological structures with reference to the geological time scale. Numerous horst and graben structures (ridges and sub-basins) as well as a number of master faults were delineated which serve as vital information with regard to hydrocarbon prospects and earthquake vulnerability, respectively. Based on the information obtained from this integrated study, a conceptual tectonometamorphic model along with sedimentation and igneous activity (ophiolitic and basaltic) has been constructed which has a significant bearing on the sequence of events that occurred during the deformational history of Kutch sedimentary basin resulting into the present day tectonic configuration.

    • Urban Heat Island studies: Current status in India and a comparison with the International studies

      K VEENA K M PARAMMASIVAM T N VENKATESH

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      Urbanization has resulted in many critical issues like increase in pollution levels, sudden climatic changes and the rise of temperature in the urban area, that is the formation of Urban Heat Islands (UHI). As the density of population rises, most of the land areas are being converted into cities and cities grows very rapidly. Due to the UHI effect, the cities are becoming hotter day by day. In India, all the metropolitan cities are victims of UHI effect and the severity of heat formation, necessitates research in this area. The present paper evaluates the trends of UHI studies in Indian cities and its out reach till 2018. Heat Island classification, methods of studying UHI in India and their limitation are discussed. Eventually a comparison of new trends of UHI studies in the world and where India lacks its growth in UHI research are included in this paper. One of the findings is that numerical modelling studies are very limited in India in this field and more focus in this area is required.

    • Robustness of best track data and associated cyclone activity over the North Indian Ocean region during and prior to satellite era

      KASTURI SINGH JAGABANDHU PANDA M MOHAPATRA

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      There are few studies focusing on analysing climatological variation in cyclone activity by utilising the best track data provided by the India Meteorological Department (IMD) over the North Indian Ocean (NIO). The result of such studies has been beneficial in decision-making by government and meteorological agencies. It is essential to assess the quality and reliability of the currently available version of the dataset so that its robustness can be established and the current study focuses on this aspect. The analysis indicates that there is an improvement over the years in the quality and availability of the data related to cyclones over NIO, especially in terms of frequency of genesis, intensity, landfall etc. The available data from 1961 onwards has been found robust enough with the advent of satellite technology. However, there can be still missing information and inaccuracy in determining the location and intensity of cyclones during the polar satellite era (1961–1973). The study also indicates undercount of severe cyclones during the pre-satellite era. Considering the relatively smaller size of NIO basin, these errors can be neglected and thus, the IMD best track data can be considered as reliable enough for analysing cyclone activity in this region.

    • Relationship between hydroclimatic variables and reservoir wetland landscape pattern indices: A case study of the Sanmenxia Reservoir wetland on the Yellow River, China

      HENG YANG JIANHUA WANG WEIHUA XIAO FAN LU YAN WANG JERKER JARSJO

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      Reservoir construction has led to the development of numerous wetlands, and these wetlands play an important role in global environmental change. In this paper, we investigate the relationship between reservoir wetlands and hydroclimatic variables. We used the MODIS land cover product to extract the wetland area of the Sanmenxia Reservoir, China. Then, various indices of reservoir wetland landscape patterns were calculated. Principal component analysis was performed to build the Sanmenxia Reservoir wetland comprehensive landscape pattern index (CLPI) to depict the changes in Sanmenxia Reservoir wetlands from 2001 to 2013. Pearson correlation analysis was used to assess their relationship. The following results were obtained. Firstly, the Sanmenxia Reservoir wetland area considerably declined and the landscape heterogeneity decreased from 2001 to 2013, especially in 2004. Secondly, the CLPI is significantly negatively correlated with annual runoff and significantly positively correlated with annual sediment discharge, annual average water level and annual shallow groundwater table in Sanmenxia Reservoir regions. Additionally, due to the decline in the reservoir wetland area, the values of Shannon’s diversity index and Simpson’s diversity index decreased in the study area. Therefore, the study suggests that maintaining a stable and healthy reservoir wetland area should be the focus of ecological reservoir management.

    • 2D and 3D numerical simulations of a reinforced landslide: A case study in NE Turkey

      HAKAN ERSOY AYBERK KAYA ZEKAI ANGıN SERHAT DAG

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      The purpose of this study is to investigate the slope stability problem that occurred in the Ulubey (NE Turkey) during the construction of a hospital building and to propose a reliable support design. The borehole applications, geophysical surveys, groundwater measurements, soil sampling and SPT were performed to establish the geotechnical model. Based on the site characterization investigations, three units were defined as sliding material, residual regolith and volcanic rocks. Strength parameters of the sliding and residual soil materials were obtained from the back analysis. The long-term performance of the double row-bore piles was proposed as support measures and was controlled using the limit equilibrium (LE) and finite element (FEM) analyses methods under a dynamic condition. The 2D-LE and 2D-FEM analysis results showed that the suggested support design is reliable for long-term stability. The locations of the critical shear surface determined by 2D methods were almost the same as those obtained from 3D-FEM method and the total displacement values obtained from the 3D-FEM model were smaller thanthose obtained from the 2D-FEM model. These results indicated that 2D and 3D stability analyses were sufficient to evaluate the stability of uncomplex slope geometry when a reliable design with simple solutions was required.

    • Geochemical signatures of Late Paleocene sandstones from the Sanu Formation, Jaisalmer basin, western India: Implication for provenance, weathering and tectonic setting

      A PATRA ANIL D SHUKLA

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      Sandstones of the Sanu Formation from Jaisalmer basin, western India were studied for major, trace and rare earth element (REE) geochemistry to deduce their paleo-weathering, tectonic setting, source rock characteristics and provenance. Geochemical results suggest that these sandstones can be classified into sub-arkose, which is supported by petrographic observations. The chemical index of alteration (CIA) values indicate intense chemical weathering. The major, trace and rare earth elements concentration pattern reveals that the sediments of the Sanu Formation were derived from silicic rock sources. The elemental discrimination diagrams specifically $\rm{(Gd/Yb)_{N}}$ against $\rm{Eu/Eu}^{\ast}$ suggest the Archean provenance as source possibly Aravallis for the studied samples.

    • Assessment of spatio-temporal distribution of $\rm{CO}_{2}$ over greater Asia using the $\rm{WRF–CO}_{2}$ model

      SRABANTI BALLAV MANISH NAJA PRABIR K PATRA TOSHINOBU MACHIDA HITOSHI MUKAI

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      In-depth knowledge of global and regional carbon budget is required for effective policymaking to mitigate the global climate change. However, Asian carbon budget shows large uncertainty due to both lack of sufficient observations and detailed understanding of the existing $\rm{CO}_{2}$ observations. A regional air quality model ($\rm{WRF–CO}_{2}$) is set up for simulating atmospheric $\rm{CO}_{2}$ variations over the greater Asia region ($68–124^{0}\rm{E}$, $2^{0}\rm{S}–45^{0}\rm{N}$) for the period 2010–2012. The $\rm{WRF–CO}_{2}$ simulations are compared with observations from nine sites and a global Atmospheric Chemistry Transport Model (ACTM). The comparisons suggest $\rm{WRF–CO}_{2}$ simulation is able to capture large scale features in the observed variabilities, with varied ability at fine scales depending on representation of surface fluxes and meteorology around the observation sites. Analysis of $\rm{CO}_{2}$ signals from individual flux components suggests that ocean flux has least contribution to the $\rm{CO}_{2}$ variation (<10%). Four sites (Mt.Waliguan, Nainital, Cape Rama and Lulin) show dominance of biospheric flux over fossil flux to the $\rm{CO}_{2}$ variation (>80%). $\rm{CO}_{2}$ mixing ratios are found to be maximum in northern hemisphere (NH) winter over East Asia, while they are maximum in NH spring over Indian subcontinent. Observed peak-to-trough seasonal amplitude is lowest (4.5 ppm) for the site Bukit Koto Tabang, Indonesia and highest (29.5 ppm) for Shangdianzi in China. Statistical analysis from monthly mean $\rm{CO}_{2}$ time series shows that correlation coefficient and normalised standard deviation with observations, are generally equal or better for the $\rm{WRF–CO}_{2}$ than the coarser resolution ACTM. Study of synoptic scale $\rm{CO}_{2}$ variations shows that the $\rm{WRF–CO}_{2}$ is able to better resolve daytime signatures than those in the night. Year-to-year $\rm{CO}_{2}$ variations of seasonal cycle amplitude is highest ($\sim 5 \rm{ppm}$) at Nainital, India compared to all other sites.

    • Phase petrographic, thermobarometric and petrochemical significance of Cretaceous mafic dykes along Nongchram Fault Zone of Swangkre–Rongmil area of Shillong plateau, NE India: Implications for genetic link to Kerguelen mantle plume

      NIVA RANI DEVI

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      The present study elucidates the phase petrographic and petrochemical signatures of a group of Cretaceous maBc dykes emplaced in the Precambrian gneissic basement complex in the western part of the Shillong plateau, NE India, in order to trace their petrological, geotectonic, geothermobarometric and oxybarometric status. The whole rock geochemistry discriminates the dykes as basaltic andesites and basaltic trachyandesites genetically related to each other and derived from common parent magma. The enrichment in LREE relative to HREE and HFSE, systematic Nb anomalies, moderate MREE to HREE fractionation suggests variable depths of melting of slightly enriched mantle source in the garnet stability field. As per geochemical modelling, the studied dykes are derived by 3–5% non-modal batch melting of garnet peridotite source at melting depth of $\sim 65–80\rm{km}$. The clinopyroxene thermobarometry reveals a temperature span of $1250–800^{0}\rm{C}$ and <2 kb pressure of crystallization for the dykes. The oxygen fugacity (16.82–18.25) indicates extremely reducing conditions at the time of cooling. The very good correlation of petrochemical and phase chemical data with Kerguelen plume derived Rajmahal Group II basalt, Sylhet volcanics and some ODP (ocean drilling project) sites from Kerguelen basalts implicate a genetic link of the studied dykes with Kerguelen mantle plume. Finally, the present study deciphers subalkaline nature of the studied dyke rocks that have been generated by tholeiitic magmas probably in an anorogenic extensional environment. But we need more geochemical data especially good isotope geochronologic data to get a clear picture of the studied dyke.

    • Interpretation of resistivity data using 3D Euler deconvolution and Radially Averaged Power Spectrum

      SHOVANA MONDAL SHALIVAHAN SRIVASTAVA ASHOK K GUPTA

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      Different electrode configuration in resistivity measurements over the same geologic structures generally produce different anomaly patterns. This is related to the position of the structure concerning the electrodes. Given the above, a unified approach has been proposed using the concept of analytical signal to interpret the resistivity data as electric potential follows Laplace’s equation. We interpret the data sets using Euler deconvolution and Radially Averaged Power Spectrum (RAPS) to determine both lithological boundaries and units and compare the results with inverted resistivity section. We analysed the resistivitydata using electrical resistivity tomography (ERT) technique over conducting dyke and vertical fault for Wenner and dipole–dipole arrays, respectively. The obtained structural indices for dyke and fault are 1.0 and 0.6, respectively. The results from Euler depth solutions match well with the inverted resistivity section. Subsequently, two field examples one each over ground water and mineral exploration were analysed. The delineated lineaments over ground water exploration matches fairly well with the available results. In addition, some additional lineaments are also mapped. These new features could be azone of interest for a detailed survey. The depths from Euler depth solutions and RAPS are in agreement. However, no depth information was available earlier. The data for mineral exploration have been acquired by ERT technique with a profile length of $\sim 500 \rm{m}$ over Dhanjori Basin, Jharkhand, India. The Euler depth solution and RAPS indicated the presence of two interfaces at an average depth of 8 and 20 m and 7 and 21 m, respectively. The first interface is present all along the profile, whereas the second interface liesbetween a part of the profile. The location and depth of these are in broad agreement with the resistivity sections obtained from ERT/AMT and borehole data. A borehole in the vicinity of the survey area indicated the presence of two interfaces. The first interface coincides with the soil depth and the second interface coincides with the sulphide mineralization.

    • Observed variability of the East India Coastal Current on the continental slope during 2009–2018

      S MUKHOPADHYAY D SHANKAR S G APARNA A MUKHERJEE V FERNANDO A KANKONKAR S KHALAP N P SATELKAR M G GAONKAR A P TARI R R KHEDEKAR S GHATKAR

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      We describe the variability of the East India Coastal Current (EICC) during 2009–2018 using data from ADCP (acoustic Doppler current profiler) moorings deployed on the continental slope in the western Bay of Bengal. The four moorings are deployed off Gopalpur ($19.5^{0}\rm{N}$), Visakhapatnam ($\sim 18^{0}\rm{N}$), Kakinada ($\sim 16^{0}\rm{N}$), and Cuddalore ($\sim 12^{0}\rm{N}$) on the Indian east coast. The longer data record allows us to attach a statistically more robust basis to the conclusions drawn by Mukherjee et al. (2014) on the basis of four years (2009–2013) of ADCP data. The data confirm that the seasonal cycle dominates the variability of the EICC. The amplitude of the annual band varies over the time series. In the intra-annual band, the variability switches between the semi-annual and 120-day bands off Gopalpur, Visakhapatnam and Kakinada, but the semi-annual band is stronger than the 120-day band off Cuddalore throughout the time series. Upward phase propagation is common in the seasonal bands, but downward phase propagation is common in the intra-annual band of Cuddalore during the summer and winter monsoons, leading to stronger undercurrents there. Off Cuddalore, even the annual EICC appears as a shallow current. In contrast, the EICC appears as a deep flow of Gopalpur, Visakhapatnam, and Kakinada particularly during the spring inter-monsoon. This deep flow is evident at these locations even in the intraseasonal (30–90-day) band; the longer data set suggests, however, that the intraseasonal variability does not necessarily peak during spring. The annual EICC is coherent along the coast, but it is only the semiannual band that shows a comparable coherence between Kakinada and Cuddalore: in the 120-day and intraseasonal bands, the EICC decorrelates along the coast. Wavelet analysis suggests significant variability at sub-annual periods. The sub-annual EICC exceeds $20 cm s^{-1}$ on many occasions, but it too decorrelates along the coast. The long ADCP record allows us to confirm the dominance of seasonality in the EICC regime in a robust fashion; the data show that the EICC tends to flow in its canonical poleward (equatorward) direction during spring (winter). This dominance of seasonality enhances the predictability of the EICC.

    • Episodic ferricretization of the Deccan Laterites (India): Inferences from ore microscopy, mineral magnetic and XRD spectroscopic studies

      JYOTIBALA SINGH S J SANGODE M F BAGWAN D C MESHRAM ANUP DHOBALE

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      Studies based on sampling a $\sim 40 \rm{m}$ thick profile comprising the basalt protolith, saprolitic horizon and various levels of ferricretization in the Deccan upland lateritic sequence of the western Maharashtra (India), indicated episodic nature of lateritization. Mineral magnetism precisely demarcated the ferrimagnetic to anti-ferromagnetic (fm/afm) boundary at the base followed by various stages of lateritic developments in the upper horizons. The fm/afm boundary can be traced in field using magnetic susceptibility and therefore provide a datum for laterite base-level mapping. Ore microscopy details the inter-association and paragenesis of amorphous and crystalline varieties of iron oxide minerals (hematite, limonite, goethite) that are further modified by allochthonous inputs and changes in porosity. The lowermost horizons show silcretization, while the XRD studies record sporadic kaolinitic occurrence throughout the profile with gibbsite appearing in the upper part of the profile. Combination of mineral magnetic and ore microscopic observations depict frequent lateral inputs possibly during periods of heavy precipitation arresting and further reclaiming the process of lateritization to produce large composite thicknesses of the Deccan lateritic sequence without matured lateritization.

    • Comparative assessment of two RegCM versions in simulating Indian Summer Monsoon

      S MAITY

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      In the present study, sensitivity of Indian Summer Monsoon (ISM) to the cumulus convection scheme (CCS) is assessed using Regional Climate Model (RegCM4.4.5). Seasonal scale (May–June–July–August–September) simulation of the model forced with European Centre for Medium Range Weather Forecasts reanalysis data (ERA interim) is carried out for the consecutive three monsoon years 2007, 2008 and 2009. Four major CCS (MIT, Grell, Tiedtke and Kain–Fritsch) are employed. Model simulated results are validated with various observed and reanalysis datasets. In addition, the model results are also compared with that of its earlier version (RegCM4.1). Detailed analysis reveals that the model’s ability to delineate large scale ISM features such as Heat Low, Tibetan high, Somali Jet, Tropical Easterly Jet (TEJ), Sub-tropical Westerly Jet (STWJ) are fairly well using multiple CCS options. Fairly, better model performance is identified while Grell over ocean and MIT over land (GO_ML) is used. This scheme exhibits relatively lower warm (cold) bias over entire northwest and partially central India (peninsular and other parts of India). Both lower and upper level circulation pattern including TEJ and STWJ are better simulated by GO_ML scheme. Simulated distribution of precipitation is also more realistic and closed to TRMM data using that scheme. Further comparison of results from two model versions indicates that the simulation with recent version (4.4) is more realistic than that with the earlier version (RegCM4.1). The study concludes that RegCM4.4 with GO_ML would be the optimal combination when overall performance of the model is taken into consideration.

    • Multi-approach synergic investigation between land surface temperature and land-use land-cover

      PRASENJIT SAHA SUBHAJIT BANDOPADHYAY CHANDAN KUMAR CHANDANA MITRA

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      Rapid urban expansion and associated land-use land-cover (LULC) change in India have emerged as a serious environmental threat that accelerates the impacts of urban heat island intensity (UHII). Three independent investigations have been conducted in this study using a series of Landsat data. The objectives of this work are: (1) To predict the near-future LULC scenario using an integrated model; (2) To understand the connection between band mean for particular LULC class with LST; (3) To analyze the temporal relationship between different types of built-up clusters and LST. The LULC and LST maps reveal that LST increases from $27.01^{0}$ to $33.86^{0}\rm{C}$, whereas built-up areas rise from 6.93% to 27.10% during 1988–2018, respectively. We observed that the near-future LULC scenario of KMA shows a huge expansion of built-up areas paid by decreased vegetation and open spaces. A clear significant correlation has been found between band mean and LST in all three Landsat sensors with the $R^{2} = 0.84$; $p$<$0.02$ for Landsat 5 TM, $R^{2} = 0.91$ and $0.99$; $p$<$0.01$ and $0.00$ for Landsat $7 \rm{ETM+}$, and $R^{2} = 0.88$; $p$<$0.01$ for Landsat 8 OLI in connection to our second objective. However, no agreement has been found between different built-up clusters and LST over 30 years of observation. For the first time, this study established the interconnectivity between bands of Landsat sensors and LST. The temporal relationship between different built-up clusters and LST have reviled also for the first time. Beside this, the rising rate of built-up areas was observed by the integrated model. Such alarming condition demands immediate attention to sustainable, and scientific land use regulations under new urbanism policy.

    • Evidence of Archaean metamorphism from the Yerrabali schist belt of Eastern Dharwar craton from EPMA dating of monazite

      SANKHA DAS SANDIP NANDY G RAMACHANDRAN SHAMPA KHAN

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      The Dharwar craton is divided in to the Western and Eastern Dharwar craton (WDC and EDC) by the N–S trending Chitradurga Shear zone. The EDC mainly consists of late Archean granites interspersed with N–S trending linear schist belts. The Yerrabali Schst belt (YSB) is located at the north-eastern corner of the EDC, near the Karimnagar granulite belt. The YSB is metamorphosed in middle-upper amphibolite facies and consists of Banded Magnetite Quartzite (BMQ), ferruginous quartzite, ultramafics, quartz–cordierite–gedrite $\pm$ garnet bearing quartzite, dolomite, amphibolite, deformed metapyroxenite, tremolite schist, sillimanite–garnet–cordierite schist, and dolerite dykes. We have dated monazites in the sillimanite–garnet–cordierite schist, exposed at the SW part of the YSB by EPMA chemical method. So far no dates are available from the YSB. The monazite chemical ages with three distinct populations, viz., $2658 \pm 42$, $2817 \pm 19$ and $3097 \pm 34 \rm{Ma}$, probably correspond to three distinct metamorphic phases. The peak metamorphism at around 2800 Ma corresponds with the garnet and cordierite growth. A temperature of $673^{0}\rm{C}$ and a pressure of 4.7 kb have been estimated for peak metamorphism.

    • REE mineral chemistry and the nature of REE mineralization: A study from felsite dykes of Phulan area, Siwana Ring Complex, Rajasthan, India

      UTPOL KUMAR DAS ARINDAM GANTAIT

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      Neo-Proterozoic Siwana Ring Complex (SRC) comprises per alkaline rocks of Malani Igneous Suite,viz., rhyolite, granite, and late phase microgranite and felsite dykes. Phulan area, lying at the north-easternmargin of SRC exposes a small body of rhyolite (<$1.0 \rm{km}^{2}$) containing feldspar + quartz + aegirine + rebeckite and is cut by dykes of felsite. These felsite dykes have a general NNW–SSE trend andvary from 60–200 m long and 0.10–2.50 m wide. These dykes are composed of quartz, alkali feldspar,aegirine and opaques. These felsite dykes were sampled and analyzed using inductively coupled plasmamethods. Of special significance is the enrichment of trace elements and rare earth elements (REE) in thefelsite dykes. These include up to 1.17% Ce, 0.6% La, 0.8% Y, 0.12% Dy, 169.25 ppm U, 571 ppm Th,1385 ppm Nb, 9944 ppm Zr. These dykes are peralkaline in nature and show negative europium (Eu)anomaly. In this study, the authors attempted to characterize REE bearing phases of the felsite dykes ofPhulan area, SRC with respect to their geneiss. REE bearing phases identified in felsite dykes aremonazite, bastnaesite, parisite, eudiyalite, allanite, perreierite and tritomite. Monazite, perreierite,allanite and tritomite are mostly found to be of magmatic in origin whereas bastnaesite, parasite andeudiyalytes occur both as magmatic and as well as of hydrothermal types. Magmatic REE minerals aremostly formed during crystallization of REE rich magma. In felsite dykes, Zr/Hf ratio varies from 23 to 31and Nd/Ta ratio ranges from 7 to 44. These two ratios are positively correlated and indicators ofhydrothermal fluid influx.

    • Groundwater exploration in limestone–shale–quartzite terrain through 2D electrical resistivity tomography in Tadipatri, Anantapur district, Andhra Pradesh

      DEWASHISH KUMAR KARRI RAJESH SETBANDHU MONDAL TAUFIQUE WARSI R RANGARAJAN

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      Two-Dimensional (2D) Electrical Resistivity Tomography (ERT) survey was carried out at 11 sites within an area of $10 \rm{km}^{2}$ to delineate deeper potential groundwater zones in a complex geological terrain underlain by quartzite, shale and limestone formations with varied resistivity characteristics. The area is in medium rainfall zone in Tadipatri mandal of Anantapur district, Andhra Pradesh state, India. The investigation was carried out to meet the growing demands of water supply. Interpretation of the highdensity 2D resistivity dataset results revealed potential zones at only three sites in Tummalapenta, Ayyavaripalle and Guruvanipalle villages within the depth zone of 24–124 m. A major fault zone orientedin EW direction is mapped at Tummalapenta site. Based on high resolution geophysical data interpretation and significant anomalies, four boreholes were drilled in complex, viz., limestone, shale and quartzite formations up to a maximum depth of 192 m in the area with the yield ranging from $300$ to $\sim 5000$ liter per hour (lph). These four anomalous drilled borehole sites corroborates with the aquifer zone delineated through ERT technique. The aquifer parameters estimated from pumping tests show that the transmissivity varies between $\sim 0.3$ and $\rm{179.5 m^{2}/day}$ while the storage coefficient ranges from 0.137 to 0.5 indicating large variation in aquifer characteristics of the system in a smaller area. Suitable water conservation measures were suggested for improving the groundwater condition and yield of the pumping wells.

    • Latent heat Cux variation during the warming phase of intraseasonal oscillations over northern Bay of Bengal

      SIMI MATHEW G LATHA R VENKATESAN

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      The sensitivity of latent heat flux to the warming phase of intra-seasonal oscillation in the Bay of Bengal is studied with the help of in-situ data. This was analyzed from 2012 to 2015 with the help of data obtained from moored buoys deployed in the northern Bay of Bengal. The annual secondary peaks in sea surface temperature is observed in the northern Bay of Bengal associated with the warming phase of the intra-seasonal oscillation during southwest monsoon season, with net heat flux dominantly governing the mixed layer temperature. An increase in the release of latent heat flux from the northern bay is observed with the warming phase of intra-seasonal oscillation, which again leads to cooling of sea surface temperature. Higher latent heat flux release associated with the intra-seasonal warming phase during southwest monsoon season has intrigued us to study the sensitivity of latent heat flux with sea surface temperature. The sensitivity of gradient in saturation specific humidity is comparatively higher than the sensitivity of wind speed to sea surface temperature variations during southwest monsoon season. The gradient in sea–air saturation specific humidity is largely driven by saturation specific humidity of air ($Q_{a}$) during both the seasons. However, the correlation of gradient in saturation specific humidity with surface saturation specific humidity is higher during southwest monsoon season compared to northeast monsoon season. Thus, the warming phase of sea surface temperature associated with intra-seasonal oscillation during southwest monsoon season always lead to an increase in latent heat flux release, favoured by high sensitivity of surface saturation specific humidity to variations in sea surface temperature.

    • Shell weights of foraminifera trace atmospheric $\rm{CO}_{2}$ from the Miocene to Pleistocene in the central Equatorial Indian Ocean

      TANVI V MUNGEKAR SUSHANT S NAIK B NAGENDER NATH DHANANJAI K PANDEY

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      The Maldives Sea is a region dominated by the South Asian monsoon (SAM) and at present, a $\rm{CO}_{2}$ source to the atmosphere. Ti/Al elemental ratios from Site U1467 and U1468 recovered from the Maldives Sea show a gradual increase from $\sim 12 \rm{Ma}$ and indicate terrigenous inputs to this region associated with increasing wind intensity associated with initiation of the SAM. Shell weights of planktonic foraminifera, Globigerinoides trilobus have been used to understand variations in surface water carbonate ion concentration for the last 20 Ma. Shell weights show a good correspondence with global $\rm{CO}_{2}$ records and show heavier shell weights during the colder periods than compared to warmer intervals which reveals that the Maldives Sea behaved similar to other tropical oceanic regions in terms of its surface water carbonate chemistry. A significant decrease in $\rm{CaCO}_{3}$ wt.%, decrease in foraminifera shell weights and dissolution of spines along with an increase in organic carbon (OC%) towards 10.5 Ma is linked to the reduced carbonate deposition and increased productivity during monsoon which is a feature in all tropical sediment cores. Lower shell weights and dissolution features on foraminiferal shells were observed during periods of intense Oxygen Minimum Zone (OMZ) suggesting calcite dissolution due to an increase in bottom water $\rm{CO}_{2}$.

    • Deep insight to the complex aquifer and its characteristics from high resolution electrical resistivity tomography and borehole studies for groundwater exploration and development

      DEWASHISH KUMAR SETBANDHU MONDAL TAUFIQUE WARSI

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      Discovering and locating the source and availability of groundwater in a plateau region of Chhotanagpur gneissic complex, where there is a varied hydrogeological characteristics, is a crucial task for earth scientists. One such region located at Garh Khatanga near Ranchi, Jharkhand, India was closely studied for groundwater assessment and exploration. High resolution electrical resistivity tomography 2D data were acquired to probe deep inside the earth up to a maximum depth of 220 m using state-of-the-art electrical resistivity tomography technique and mapped geoelectrical subsurface images at 16 sites in three different blocks along a 7.2 km line for prospecting and exploration of groundwater resources. The geophysical inversion of the 2D resistivity data revealed prospect groundwater scenario at six sites based on the hydrogeological interpretation and the significant resistivity contrast between the highly weathered/fractured and the massive rocks. The modelled resistivity sections revealed different degree of weathered, fractured and saturated weathered/fractured strata as well as clearly indicated the presence of a totally hard massive rock within the subsurface lying between $\sim$30 and 220 m depths. The geophysical anomalies were confirmed and validated by borehole drilling at four sites up to a maximum depth of 215 m with yields ranging from 2.0 to 4.25 inch, which is equivalent to 5632–63769 l/hr of groundwaterexploitation. These yields of groundwater resources are rated as good aquifer(s) in the plateau region of Chhotanagpur gneissic complex. The characteristics resistivity for fracture zone varies from 140 to 1300 $\Omega$m, while for saturated weathered/fractured it ranges from 10 to 1000 $\Omega$m. On joint interpretation of the 2D resistivity models and the borehole lithology data, it clearly shows the average resistivity of the aquifer zone lies in the range 50–500 $\Omega$m. The present study along with the conceptual geological models provided a sound knowledge of hard rock hydrogeology in the plateau region with complex geological settings and these helped to achieve significant results for groundwater exploration and development of the resources of the studied area as well as take up such challenging work in exploring the prospect groundwater resources in other similar geological setting of the country.

    • Analysis of seismic site characterization of the Isparta basin (southwestern Turkey) using passive surface-wave method ($\rm{ReMi^{TM}}$) and borehole data

      ALI SILAHTAR MEHMET ZAKIR KANBUR GuNAY BEYHAN

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      This study presents a site classification of the Isparta basin situated at the upper part of the Isparta Angle, which is one of the most important tectonic components in Turkey. The local conditions of the basin sediments may significantly increase ground motions from earthquakes and cause more structural damage. $V_{s30}$ is one of the base parameters used for the determining site classification. In this study, refraction microtremor ($\rm{ReMi^{TM}}$) method was used to determine the shear-wave velocities structure and hence classifying the site characterization of Isparta basin. The data were collected at 172 locations and converted to shear-wave velocity–depth models and shear velocity ($V_{s}$) maps were created. The $V_{s}$ structures were compared and evaluated with the current borehole records compiled from the area. The site classification map of the Isparta basin was prepared by using the $V_{s30}$ map and considering the National Earthquake Hazards Reduction Program (NEHRP) criteria. According to this map, the soft alluvial deposits of the central basin are mostly classified as D, and a few are classified as C. The soil class at the southern part of the basin (old urbanization area of the city) increases to C class due to which the tuff–tuffite content increases. The rock units such as Mesozoic carbonates and Cenozoic flysch located around the basin are classified as A. The soil class B, appears between the class A rocks and the alluvial basin, has relatively thin alluvial slope deposit overlying the rock. The classification obtained from this study may contribute to the studies on future urban planning and seismic risk assessment.

    • Simulation of coastal aquifer using mSim toolbox and COMSOL multiphysics

      SRUTHI S KUMAR S DEB BARMA MAHESHA AMAI

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      Fluctuations in groundwater levels along the coast have a significant impact on the extent of saltwater intrusion into freshwater aquifers. This study aims to simulate the groundwater flow and solute transport in the region by using the mSim toolbox in the MATLAB and COMSOL Multiphysics. The investigation is focussed on a micro-basin of Pavanje river located along the west coast of India. The model results are calibrated and validated against the field observations. The results show that the variation of the water table over the year is significant and range from about 3–14 m. There exists a reasonable correlation between the simulated and observed values of groundwater level and salinity. The wells that are most vulnerable to seawater intrusion in the region are identified. The COMSOL model estimated a salinity range of 0–20 mol/m3. Additionally, the model is used to understand the response of coastal aquifer to various stress scenarios. The study reveals that reduced recharge rate with increased pumping has a serious impact on aquifer system.

    • Observational aspects of tropical mesoscale convective systems over southeast India

      A MADHULATHA M RAJEEVAN T S MOHAN S B THAMPI

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      To enhance the knowledge of various physical mechanisms related to the evolution of Tropical Mesoscale Convective Systems (MCSs), detailed analysis has been performed using suite of observations (weather radar, electric field mill, surface weather station, flux tower, microwave radiometer and wind profilers) available at Gadanki ($13.5^{0}\rm{N}/79.2^{0}\rm{E}$), located over southeast India. Analysis suggests that these systems developed in warm, moist environment associated with large scale low level convergence. Significant variations in cloud to ground (CG) lightning activity indicate the storm electrification. Deep (shallow) vertical extents with high (low) reflectivity and cloud liquid water; dominant upward (downward) motionreveals variant distribution in convective (stratiform) portions. Existence of both +CG and –CG Cashes in convective regions, dominant –CG in stratiform regions explains the relation between lightning polarity and rain and cloud type. Sharp changes in surface meteorological variables and variations in surface fluxes are noticed in connection to cold pool of the system. Increase (decrease) in temperature, moisture and equivalent potential temperature ($\theta$e) within the boundary layer in convective (stratiform) regions associated with latent heat warming (cooling) of air parcel are apparent. Presence of updrafts and downdrafts in convective region and dominant downdrafts in stratiform regions are evident from vertical velocity measurements. Isentropic upgliding (downgliding) illustrate the existence of isentropic ascents (descent) of air parcels in the storm vicinity. Veering (backing) of wind due to warm (cold) and moist (dry) air advections demonstrated the formation of $\theta$e ridge in storm environment. Blend of observations provided considerable insight of electrical, microphysical, thermodynamic, dynamic and kinematic features of MCS.

    • New evidence for a thin crust and magmatic underplating beneath the Cambay rift basin, Western India through modelling of EIGEN-6C4 gravity data

      AVINASH KUMAR CHOUHAN PALLABEE CHOUDHURY SANJIT KUMAR PAL

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      The Cambay rift basin (CRB) is an intracratonic rift in the western part of India. The basin assumes great importance in petroleum exploration owing to the presence of thick hydrocarbon bearing sedimentary rocks. Previous investigations using deep seismic soundings (DSS), gravity and heat flow data reveal that the CRB is characterised by a thin crust, high heat Cow and high density lower crust. In this study, a detailed crustal structure of the basin is presented by performing a 2.5D density modelling of the EIGEN-6C4 gravity data. Present study attempt to find a plausible explanation for the variation in the Bouguer anomaly (BA) values from +20 to -50 mGal within the basin. It refined the crustal model that is constrained using results from radial average power spectrum (RAPS) analysis of gravity data along with previous seismological and geophysical studies, which reveals that the values of average sedimentary and Deccan Traps thickness are in the order of 4–5 and 1.5–3 km, respectively, along the rift. It also presents possible evidences for a high density underplated layer of thickness 7–15 km along the central part of the CRB. To study the deep-seated features, upward continuation of the BA is carried out at heights of 30, 40 and 50 km. The extension of underplating layer is noticed in the present crustal model and in the upward continued BA in the western part, while it merges with the Moho in eastern part of the CRB. The Moho depths, varying from 31 to 37 km, are found to be shallower inside the CRB than the surroundings. It is inferred that the high BA values in the basin are due to the combined effect of the high density underplated layer in the lower crust and a shallow Moho.

    • Percolation pond with recharge shaft as a method of managed aquifer recharge for improving the groundwater quality in the saline coastal aquifer

      M C RAICY L ELANGO

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      The deterioration of groundwater quality has become a serious problem for the safe drinking water supply in many parts of the world. Along coastal aquifers, the saline water moves landward due to several reasons even though significant rainfall is available. The objective of the present study is to investigate the impact of a combined recharge structure including a percolation pond and a recharge shaft in improving the groundwater quality of the surrounding area. The area chosen for this study is Andarmadam, Thiruvallur district of Tamil Nadu. As a part of the study, a suitable site was selected for the construction of a percolation pond based on preliminary field investigations in 2012. Three piezometers were also constructed near the percolation pond to investigate the impact of the structure on groundwater recharge. Further, a recharge shaft was added to this structure in 2013 to overcome the clogging issues at the pond bottom and to enhance the recharge. The impact of the percolation pond on groundwater was assessed by comparing the periodical groundwater level fluctuations with rainfall in the area. The fluctuations in groundwater level near the percolation pond show variations before and after the construction of recharge shaft. The amount of water recharged through the percolation pond during the water year 2012–2013 was estimated as $250–300 \rm{m}^{3}$. The volume of recharge was calculated to be increased more than twice after the construction of recharge shaft inside the percolation pond, on the assumption that recharge through the pond surface remained almost same as before. The dilution of ionic concentration in water was three times higher after the construction of recharge shaft. The long-term groundwater quality in the surrounding area of the pond improves gradually with time. The total dissolved solids (TDS) decrease considerably with time due to the dilution of dissolved solids in water with the fresh water recharging into the aquifer. The Wilcox diagram of most of the water samples after the construction of the recharge structure fall in the excellent to good category, indicating improvement in irrigation water quality.

    • Contrasting kinematics of brittle-shears within the Salem–Attur and Bhavani shear zone, south India: Tectonic implications

      C ANANTH SUBHADIP BHADRA ABHISHIKTA GOSWAMI

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      We document kinematics and rheological behaviour of brittle shears ($\sim$50 cm wide) postdating solid-state tectonic fabric in the Salem–Attur (SASZ) and Bhavani (BSZ) shear zone that constitute a Paleoproterozoic ($\sim$2500 Ma) suture juxtaposing disparate granulite blocks in south India. We constrain brittle deformation mechanisms from established relationship between changing orientation of deflected strain marker (quartz vein) and foliation within the shear band with respect to their orientation outside the shear band. Quartz c-axis orientation in charnockite (host lithology) and phyllonite (reworked charnockite) from the SASZ show presence of mixed basal $\langle a \rangle$ (low-T) and prism $\langle a \rangle$ (high-T) slip, and single basal $\langle a \rangle$ slip mechanism, respectively. This suggests considerable cooling of the granulite block prior to the onset of brittle shearing. Distribution of strain parameters – effective shear strain ($\it{\Gamma}$), shear strain ($\it{\gamma}$), stretch $K_{2}$ along intermediate strain axis Y – from margin to the centre of the shear band, show peaked distribution with a single maximum at the shear zone centre. This implies rheological-weakening/ strain-softening induced localizing shear zone character. Kinematically heterogeneous strain distribution during brittle shearing varies from transpression dominated for the BSZ to transpression-to-transtension switchover for the SASZ. Demonstrably, contrasting cooling-exhumation, hitherto unexplored, characterizes post-accretionary tectonics along the paleo-suture zone.

    • Fluvial facies and petrography of Late Pleistocene Baneta sediments, Central Narmada Basin, Madhya Pradesh, India

      M G KALE ASHWIN S PUNDALIK DEVENDER KUMAR

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      Baneta Formation, comprising of fining upward sequences of pebbly conglomerate, sandstone and siltstone, exhibits development of five distinct lithofacies, viz., massive pebbly conglomerate, large scale tabular cross bedded sandstone, horizontal parallel bedded coarse-grained sandstone, parallel laminated fine-grained yellowish sandstone and siltstone; representing channel lag, point bar and overbank flood plain deposits of mixed load meandering river. In these sediments, development of nodular, buckled bedded calcrete, rhizoliths and tepee is noticed. Granulometric studies of these sediments revealed presence of wide range of grain size classes, polymodal grain size distribution, moderate to very poor sorting, positive skewness and leptokurtic nature, supporting fluvial environment of deposition. Lithic arenitic nature, heavy mineral assemblage with dominance of augite and low ZTR index of these sediments indicate mineralogical immaturity and presence of illite, kaolinite and montmorllionite together with geochemical composition indicate their derivation from mixed provenance of Precambrian granite, metapelites, Vindhyan Supergroup, Gondwana Supergroup, Deccan trap basalt, and laterite. The thin sections studies reveal signatures of meteoric phreatic and vadose zone diagenesis related with semi-arid climate and subaerial exposure. The $\delta^{13}\rm{C}$ and $\delta^{18}\rm{O}$ content of calcretes indicate their pedogenic and/or shallow groundwater origin under semi-arid climatic conditions, and C3–C4 mixed vegetation with dominance of C4 vegetation. $\rm{OSL}$ and $^{14}\rm{C}$ dates of the samples from Baneta Formation suggest deposition of these sediments in Late Pleistocene.

    • Trend analysis of atmospheric temperature, water vapour, ozone, methane and carbon-monoxide over few major cities of India using satellite data

      POOJA JINDAL PRADEEP KUMAR THAPLIYAL MUNN VINAYAK SHUKLA SOM KUMAR SHARMA DEBASHIS MITRA

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      In this study, decadal trend analysis of atmospheric temperature, water vapour, ozone, methane and carbon-monoxide has been presented over few major cities of India using Aqua-AIRS products from 2003 to 2012. The atmospheric column is studied in few atmospheric layers, viz., surface-850, 850–500, 500–100, 100–50 and 50–1 hPa for temperature, water vapour and ozone. However, $\rm{CH_{4}}$ and $\rm{CO}$ results are presented in total column amounts. Non-parametric Mann–Kendall test has been applied to investigate the trends of annual means of parameters and Sen’s slope estimate has been used to find the rate of the change, if there is a trend. The layer average temperature (LAT) has been found to be increasing in lower troposphere (surface-850 hPa) and decreasing in lower stratosphere (100–50 hPa). The warming trend over Chennai is found to be not limited in lower tropospheric region, but extended in 850–500 hPa layer also. However, LAT(850–500 hPa) has decreasing trend over Thiruvananthapuram. LAT in 500–100 hPa has significant decreasing trend only over Ahmedabad. The decreasing LAT trend in 100–50 hPa is quite prominent with significant decreasing trends over Mumbai, Ahmedabad, Kolkata and Hyderabad. The layer integrated water vapour (LIWV) is found be increasing mainly in surface-850 hPa and 850–500 hPa layers. The decreasing trend of LIWV has been observed only over Ahmedabad in 500–100 hPa layer. For total column water vapour, the trends are mostly increasing, however, it is statistically significant only over Hyderabad. The layerintegrated ozone has been found to be increasing in troposphere and decreasing in lower stratosphere. The increasing trend of ozone in troposphere is most prominent in lower-mid tropospheric region (850–500 hPa layer). No significant trend has been observed for total column ozone. Total column methane has shown significant increasing trend over all cities with very good significance level. However, for total column carbonmonoxide, the trends are decreasing and the decreasing trends are significant over Delhi and Mumbai.

    • A new Western Disturbance Index for the Indian winter monsoon

      T M MIDHUNA P KUMAR A P DIMRI

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      The Himalayas are storehouse of freshwater, which is of utmost importance for agriculture and power generation for billions of people in India. Winter (December, January and February: DJF) precipitation associated with Western Disturbances (WDs) influences Himalayan climate, glaciers, snow-water storage, etc. One-third of annual precipitation over northern Indian region is received during winter. Winter WDs are synoptic-scale systems embedded the subtropical westerly jet (SWJ). Their orographic interaction with the Himalayas intensifies precipitation over Pakistan and northern India. Precipitation due to WDs and associated dynamics are termed as Indian winter monsoon (IWM). The present study focuses on the WDs climatology using National Center for Environmental Prediction/National Center for Atmospheric Research, US (NCEP/NCAR) reanalysis data. The period of study spans over 29 years (1986–2016) during which $\sim500$ WDs were observed as per India Meteorological Department (IMD) daily weather report. Precipitation, vertical distribution of wind and geopotential height during the passage of these WDs are analyzed. Importantly, a new index, Western Disturbance Index (WDI), for measuring strength of IWM is proposed by using difference of geopotential height at 200 and 850 hPa levels. The index is able to capture changes in 500 hPa wind, air temperature and mean sea level pressure during the passage of WDs.

    • Development of framework for assessment of impact of climate change in a command of water resource project

      R K JAISWAL A K LOHANI H L TIWARI

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      A framework comprising of four interdependent modules has been developed to analyse demand–supply scenarios under future uncertainties of climate change in an irrigation command where any mismatch can affect sustainability and wellbeing of the rural population. In the absence of runoff records, the water balance module of framework computes daily runoff from catchment considering all inputs, outputs and losses from the system. The climatic parameters and rainfall were forecasted for three future projected periods using statistical downscaling for six different climate projections. The Soil andWater Analysis Tool (SWAT), a physically based spatially distributed hydrological model and SWAT-CUP, an application for calibration and uncertainty analysis of SWAT model have been used to calibrate and validate a model for the base period (BP:1981–2015) and further applied to generate multiple future run off series to asses water availability. The module-IV was designed to compute evapotranspiration using ETo calculator (a software to compute evapotranspiration) and then irrigation demand for Tandula command in the Chhattisgarh state of India considering present overall effciency of 51% for the base (1991–2015) and future assessment periods. The analysis of all projectedscenarios suggested an increase of annual temperature from present $26.2^{0}–27.1^{0}$, $27.3^{0}$ and $27.8^{0}\rm{C}$ during near (FP-1: 2020–2035), mid (FP-2: 2046–2064) and far century (FP-3: 2081–2099) periods, respectively, may demand more water which could be adversely affected by reduced rainfall. The water requirement may vary in the range of 410.4–464 MCM and supply from 426.2 to 453.2 MCM based on future projection from GCMs.

    • Observed variability of the West India Coastal Current on the continental slope from 2009–2018

      ANYA CHAUDHURI D SHANKAR S G APARNA P AMOL V FERNANDO A KANKONKAR G S MICHAEL N P SATELKAR S T KHALAP A P TARI M G GAONKAR S GHATKAR R R KHEDEKAR

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      We describe the variability of the West India Coastal Current (WICC) during October 2008 to October 2018 using data from ADCP (acoustic Doppler current profiler) moorings deployed on the continental slope off the west coast of India. The four moorings are deployed off Mumbai ($\sim 20^{0}\rm{N}$), Goa ($\sim 15^{0}\rm{N}$), Kollam ($\sim 9^{0}\rm{N}$), and Kanyakumari ($\sim 7^{0}\rm{N}$). This 10-year data set allows us to attach a statistical significance to the conclusions drawn by Amol et al. (2014) on the basis of four years (October 2008–October 2012) of ADCP data. The longer data set confirms the earlier finding that intraseasonal variability in the 30–90-day band dominates the variability of the WICC at all locations and that this intraseasonal variability peaks during the winter monsoon. The annual cycle (300–400 days) is strong and statistically significant at all locations. The phase propagates upward for the annual cycle and this phase difference is seen in the relative phases of both, the ADCP currents at 25 and 48 m as well as the 48 m ADCP and satellite-derived currents. The intra-annual (100–250 days) and intraseasonal currents show instances of both upward and downward phase propagation. The alongshore wavelet coherence is high on seasonal time scales between adjacent mooring locations and several instances of high coherence are seen even on intraseasonal time scales. Data gaps off Goa and Kanyakumari restrict the significant wavelet power to the ADCP records off Kollam and Mumbai, and the coherence analysis shows that the WICC off Kollam leads Mumbai on seasonal scales. The direction of the alongshore WICC is, however, largely determined by the direction of the significantly larger intraseasonal component. Though the climatological seasonal cycle over the whole record does show the canonical equator ward flow during the summer monsoon (June–September) and poleward flow during the winter monsoon (November–February), the scatter around the daily mean is very high.The data show that the WICC may flow in either direction on a given day of the year, with this unpredictability of direction being stronger off Kollam, where the $1-\sigma$ band of the daily mean alongshore WICC shows that it can flow in either direction in most months. The seasonality is stronger off Mumbai, where the width of the $1-\sigma$ band is less. The decade-long continuous record off Kollam and Mumbai shows that the sub-annual along shore WICC at both locations is significant and is comparable to or stronger than the annual component.The cross-shore sub-annual current is also strong off Kollam and is seen to be associated with eddy-like circulations.

    • Mapping of basement structure beneath the Kohima Synclinorium, north-east India via Bouguer gravity data modelling

      CH RAVI KUMAR N KESIEZIE B PATHAK SAUMEN MAITI R K TIWARI

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      Kohima Synclinorium is one of the most tectonically active corridors of Indian subcontinent and displays complex tectonics of the region. Mapping the basement structure beneath the Kohima Synform is, therefore, vital to provide deep insight into the understanding of the crucial thrust geometry of the region. The vertical gravity gradient anomalies and available geological evidences suggest that the underlying area is occupied by thrust geometry embedded with prominently known tectonic trends of Schuppen Belt (SB), Kohima–Patkai Synclinal (KS–PS) and adjoining Inner Fold Belts (IFB). By keeping in view the massive complex tectonic upheaval in the region, we carried out 2D Bouguer gravity data analysis using the radially averaged power spectral techniques and GMSYS modelling to map the basement depth more precisely. Our results suggest that there is a wide range of heterogeneity in the underlying undulating basement indicating an average sedimentary thickness of the order of 2.2–5.5 km. The gravity PDEPTH modelling results show that source depth varies from 2.5 to 6.5 km. There is an uplifted basement tending towards the southwestern part while gradual deepening of basement was observed towards the eastern part of the study area. The profile modelling results show the presence of basement in a depth range of 2.5–3.8, 3.8–4.0, and 3.8–4.2 km beneath Foreland Basin (FB), Kohima–Patkai Synclinal structures (KS–PS), and Inner Fold Belts (IFB), respectively. The underlying results of integrated profiles, PDEPTH and GMSYS modelling would be useful to understand the detailed basement structure and tectonic trends of Belt of Schuppen (BS), Kohima–Patkai Synclinal structures (KS–PS) and adjacent Inner Fold Belts (IFB) of north-eastern region of India.

    • GIS-based pre- and post-earthquake landslide susceptibility zonation with reference to 1999 Chamoli earthquake

      SANGEETA BAL KRISHNA MAHESHWARI DEBI PRASANNA KANUNGO

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      Landslides induced due to monsoon rainfall and earthquakes are very common phenomena in Uttarakhand Himalayas of India. For example, many such landslides got induced and reactivated by the 1999 Chamoli earthquake. In view of above, authors have made an attempt to prepare pre- and post-earthquake landslide susceptibility zonation (LSZ) maps for a part of Chamoli district, Uttarakhand, India. The novelty of this work lies in producing an LSZ map considering peak ground acceleration (PGA) as one of the controlling factors for earthquake-induced landslide occurrences and validating the LSZ map with the post-earthquake landslide inventory. For this purpose, a spatial database of seven controlling factors, i.e., slope angle, slope aspect, slope curvature, geology, distance to drainage, normalized difference vegetation index (NDVI) and peak ground acceleration (PGA) was prepared in Geographic Information System (GIS). Then, relative frequency ratio (RFR) method was adopted for the LSZ maps. The landslide inventory of 276 landslides (220 pre-earthquake and 56 post-earthquake landslides) was prepared for the study area. Firstly, an LSZ map was generated using six controlling factors excluding PGA and the pre-earthquake landslide inventory (Case I). In another attempt, the LSZ map is prepared using seven controlling factors including PGA and pre-earthquake landslide inventory to examine the influence of seismic parameter (PGA) in landslide susceptibility assessment (Case II). Subsequently, pre- and post-earthquake landslide inventory along with seven controlling factors were used to construct another LSZ map (Case III). Finally, these three LSZ maps were validated and compared with the training and testing data. In this study, a spatial predictive model for earthquake-induced landslide is developed.

    • Change of lithofacies in marine sediment core from Quaternary to Pre-Quaternary: A case study from the Central Indian Ocean Basin

      SIMONTINI SENSARMA SHYAM M GUPTA RANADIP BANERJEE SUBIR MUKHOPADHYAY

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      A distinct change in lithofacies was observed from red clay to siliceous ooze in a core from Indian Ocean. Radiolarian index species were used to ascertain the Quaternary datum levels and an age of 2.0 Ma is determined up to 125 cm depth from surface. Below 185 cm depth, the sediment core lacked radiolariantest completely. At about 50 cm from core top, the sedimentation rate decreased drastically from 0.18 to 0.05 cm/kyr with a corresponding age of 500 kyr, marking Marine Isotope Stage 13. The changes in lithofacies and sedimentation rate are further accompanied by the change in clay mineralogy from smectite rich older sediments to smectite depleted younger sediments and presence of higher amount of volcanogenic materials in the older sediments. Higher values of chemical index of alteration (CIA) and lower $\rm{K_{2}O/Al_{2}O_{3}}$ in older sediments indicate dominance of chemical weathering in the older sediments which decreased gradually towards core top. Ti normalized concentrations of elements like $\rm{Co}$, $\rm{V}$, $\rm{Cu}$, $\rm{Ni}$, $\rm{Ce}$, $\rm{Y}$ and $\Sigma\rm{REEs}$ exhibit lowest values at the transition zone above which the ratios increased steadily towards the core top. All these observations indicate a marked change in the climatic regime from late Quaternary onwards, prior to which the environment was less bio-productive.

    • Landslides assessment using geophysical and passive radon exhalation detection techniques in Murree Hills, northern Pakistan: Implication for environmental hazard assessment

      KHAWAR ASHFAQ AHMED SARFRAZ KHAN MAHMOOD SULTAN UMAIR BIN NISAR MUHAMMAD RIZWAN MUGHAL SHAHID NADEEM QURESHI

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      Geophysical investigation of three landslides in Murree Hills was carried out using geophysical techniques (i.e., seismic refraction and electrical resistivity) and geochemical tool (passive radon exhalation detection method). The seismic data was acquired by using reverse shooting scheme employing placement of source after the last active geophone in the spread. The acquired data was analyzed, and layer velocities were estimated by using Hagedoorn’s method. The resistivity data was modeled in terms of true resistivity of subsurface material by curve matching technique. The radon emission was determined as alpha track densities for each detector planted in dosimeter in the sub-surface along survey profiles. The results of all the methods employed were interpreted and correlated in the context of local geology, and also considering seasonal and anthropogenic factors. The study guides the importance of local geological structure and lithologies in the formation of thick weathering layer. The weathered layer wet/moistened through rains in the winter and summer seasons or daily use of water due to urbanization of the area, exerts more downslide force thus resulting landslides. This thickness of weathered layer is determined by using seismic refraction and resistivity methods for the three landslides (MIT, Kuldana and Chitta Mor) which is in agreement. Also, the passive radon exhalation detection technique (geochemical investigation) has delineated the stable and unstable areas within the three landslide zones. These geophysical and geochemical investigations are recommended on the major landslides of the area prior to damage control measures.

    • Source rock weathering and groundwater suitability for irrigation in Purna alluvial basin, Maharashtra, central India

      ASHOK K SRIVASTAVA PRAVIN S PARIMAL

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      Purna alluvial basin is characterized by low to high level groundwater salinity having adverse effect in a large area, however, the basin still lacks one-time data of any season regarding hydrogeochemistry and quality assessment for drinking and irrigation purposes. The present work is aimed to determine various weathering indices and estimation of groundwater quality for irrigation purpose. The interpretations are based on the study of total 158 samples, collected from dug wells (60) and bore wells (98) during both pre and post-monsoon periods of the year 2009. The plots between $\rm{Ca+Mg}\,vs. \rm{SO_{4}+HCO_{3}}$, $\rm{Na}\,vs. \rm{Cl}$ and $\rm{Na}\,vs. \rm{HCO_{3}}$ reveal that most of the samples fall below the equiline that indicates prevalence of silicate weathering. The USSL diagram (Wilcox diagram) demonstrates higher concentration of points in the fields of C2S1 and C3S1 for both the aquifers, indicating high salinity and low to medium sodium water; however, a few sample points positioned in C3S4 and C4S4 fields indicate high salinity but medium to high sodium. The values of Na%, RSC, Kelley ratio and magnesium ratio for most of samples exhibit doubtful to unsuitable categories of groundwater for irrigation from both the aquifers during pre- and post-monsoon periods. The vast data bank generated for entire basin is significant for government and non-government organizations for future planning and management.

    • Observations of carbon dioxide and turbulent Cuxes during fog conditions in north India

      M N PATIL T DHARMARAJ R T WAGHMARE SURENDER SINGH PRAKASH PITHANI RACHANA KULKARNI NARENDRA DHANGAR DEVENDRAA SIINGH G R CHINTHALU RAJ SINGH SACHIN GHUDE

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      The occurrence of thick fog for longer duration in the northern regions of India disturbs the aviation, roadtransportation and other day to day activities. To understand the turbulence properties during fog period,we measured the atmospheric turbulent parameters along with carbon dioxide concentrations in theatmospheric boundary layer using eddy covariance system. These measurements were conducted over the agricultural station, Hisar, India, during the months of January–February of the year 2017 and 2018.During this period, total five thick fog events and three moderate fog events were captured. The turbulentparameter such as friction velocity, stability, sensible and latent heat fluxes are presented with respect tofog events. During the study period, the western disturbance persists over the north Pakistan andneighborhood region which advects the large amount of moisture into the lower troposphere and furtherthrough evaporation. It enforces stable and clear sky atmospheric conditions and reduces the surfacetemperature leading to the formation of strong surface-based temperature inversion which facilitatesthe fog formation in the study region. The land surface processes with neutral stability conditions in thesurface layer, play significant role to sustain fog in the study region. The observations show substantialincrease of carbon dioxide concentration during the thick fog events. The foggy days did not depict thediurnal pattern in flux of $\rm{CO}_{2}$. The anomalies of the meteorological parameters during foggy days and clear sky are analyzed. The foggy conditions (04:00–10:00 h, IST) are found to be characterized with low wind speed, high relative humidity with remarkable fluctuations in dew point temperature. Also, the sensible and latent heat flux shows remarkable changes during foggy and clear sky conditions.

    • Implication of submarine groundwater discharge to coastal ecology of the Bay of Bengal

      KOUSIK DAS PALASH DEBNATH SRIMANTI DUTTAGUPTA SUKANTA SARKAR SUDHA AGRAHARI ABHIJIT MUKHERJEE

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      The present study is undertaken in the eastern coast of India, along the coastal tract of Bay of Bengal (BoB), to delineate the submarine groundwater discharge (SGD)-borne nutrient flux at temporal scale and their impact to coastal ecology and biogeochemical processes. Solutes chemistry, seepage meter study, stable-isotopic signature, and geophysical techniques were used to identify the surface water–groundwater interaction zone, SGD rate and nutrient flux. The estimated rate of major annual discharge of nutrient fluxes were 240 and 224 mM $\rm{m^{-2} day^{-1}}$ for $\rm{NO}_{3}^{-}$ and Fetot. The variation of solute and nutrient fluxes was depending on the load of terrestrial water masses, which is triggered by the local monsoonal meteoric recharge. The ecohydrological response to this solute flux results in spatio-temporal patterns of N and P-sensitive algal blooms in the intertidal zones. Most algae were identified as dinoflagellates and some haptophytes, with greenish and brownish hue that provides a distinct look to the coastal landscape. The algal blooms were found to be substantially influenced by the seasonal-nutrients flux and discharge location. Our study is expected to increase the understanding of a rarely reported ecohydrological response to terrestrial–marine water interactions and their implications in the tropical ocean adjoining the Indian Subcontinent.

    • Comparative analyses of Bnite element and limit-equilibrium methods for heavily fractured rock slopes

      TuMAY KADAKCI KOCA M YALCIN KOCA

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      Limit-equilibrium method (LEM) and Bnite element method (FEM) with shear strength reduction (SSR) technique are the most widely used analysis tools in slope stability assessment. Recently, researchers have reported that both factor of safety (FOS) values and failure surfaces obtained from LEM and FEM are generally in good agreement except in some particular cases. On the other hand, the consistency between two methods has not been adequately discussed for heavily fractured rock mass models by employing Generalized Hoek–Brown Criterion (GHBC). In this study, the FOS values and failure surfaces derived from LEM and FE-SSR based on GHBC were compared concerning static and pseudo-static conditions, various overall slope angles, geological strength index (GSI) values, and various water table levels. In this context, three homogeneous, highly fractured rock slope models with irregular geometry and different slope heights were generated by two-dimensional Slide and $\rm{Phase^{2}}$ software. Limit-equilibrium (LE) analyses were performed by Bishop, Fellenius, Morgenstern–Price, and Spencer techniques. The comparisons of global minimum FOS values for 431 cases and the effects of variables on two methods were investigated by statistical analyses. Consequently, it was determined that the difference between the FOS values are statistically significant. However, if the seismic coefficient is higher than 0.1 g, slope angle is higher than $34^{0}$, and the slope is assumed to be fully saturated, Morgenstern–Price is the most well-matched technique with FE-SSR than the others. For the same cases, the failure surfaces detected by Fellenius is more similar to the ones detected by FE-SSR.

    • An improved method for predicting water shortage risk in the case of insufBcient data and its application in Tianjin, China

      LONGXIA QIAN ZHENGXIN WANG HONGRUI WANG CAIYUN DENG

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      It is very important to estimate the parameters of a risk prediction model in the case of small samples. This paper proposed an improved method for predicting water shortage risk in situations when insufficient data are available. The new method (maximum entropy estimation, MEE) does not require the data about water shortage risk but only a few data about the risk factors. Twelve simulations or experiments were made to evaluate the performance of MEE under different small sample size and compared with the maximum likelihood estimation (MLE) which requires a large amount of data about risk and its factors, and two models which require small samples about risk and risk factors. The result shows that MEE performs much better than MLE, and has an advantage over the two models. Water shortage risks in 2020 in all the districts or counties of Tianjin were predicted by using the new method. The result shows that the values of water shortage risk in most of the districts or counties of Tianjin are very high when the transferred and unconventional water are not used. After using the transferred and unconventional water, all the values of water shortage risk decline considerably.

    • Petrological study of spinel peridotites of Nidar ophiolite, Ladakh Himalaya, India

      RANJIT NAYAK BIDYANANDA MAIBAM

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      Petrological study of the ultramafic rocks from the Nidar Ophiolite Complex (NOC) of the Indus Suture Zone is carried out. The study of Cr-spinels along with olivine and pyroxenes emphasizes the genesis and tectonic setting of the ultramafites. Olivine from the harzburgite is Mg-rich, with the molar ratio Mg# [$\rm{Mg/(Mg + Fe^{2+}}$)] varying between 0.91 and 0.94 and olivine in dunite between 0.92 and 0.94. Clinopyroxene from the harzburgite is $\rm{TiO_{2}}$ and $\rm{Na_{2}O}$-poor diopside ($\rm{Wo_{47–50}En_{47–50}Fs_{2–4}}$). Spinel in harzburgite shows wide Cr#, molar ratio varied between 0.26 and 0.72, and significantly higher in dunites with Cr# ranges from 0.69–0.85. Cr# of the peridotite spinel follow a depletion trend. Calculated equilibrium conditions of the samples are $800–900^{0}\rm{C}$ temperature, 32 and 40 kbar pressure, oxygen fugacity -0.09 to 0.55 log units above the FMQ buAer. Residual nature of the harzburgites and the presence of high and low Cr# spinels may be due to the genetic artifact of the different ultramafic units.

    • Estimation of groundwater abstraction induced land subsidence by SBAS technique

      S SUGANTHI L ELANGO

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      The groundwater over pumping induced land subsidence is one of the major geological hazards in the alluvial aquifers. The objective of this study is to assess the rate of land subsidence in Kolkata metropolitan area, India. Land subsidence can be estimated with high precision by Small Baseline Subset (SBAS) analysis. The advantages of this method are generation of a mean deformation map. The ENVISAT ASAR data acquired at six different periods over the study site were processed by SBAS technique. The decline in the piezometric head from the year 2003 to 2010 was about 6 m. Land subsidence velocity was $\sim$8 mm/year at Salt Lake City and Science City (near the eastern metropolitan bypass). The major cause for land subsidence is over pumping of groundwater from the confined aquifers in these areas. There is a reasonable comparison between the maximum region of land subsidence and low value piezometric head contours confirming that the over extraction of the confined aquifer of this region is responsible for land subsidence. It is necessary to control the groundwater pumping so as to arrest the declining trend of piezometric head of study area for managing the problem of land subsidence. Hence, the possible remedial measures that can be taken are reducing groundwater pumping in the study region.

    • Compositional mapping and the evolutionary history of Mare Tranquillitatis

      H BHATT P CHAUHAN P SOLANKI

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      This study signifies the compositional variability of Mare Tranquillitatis basalt and the Irregular Mare patches (IMPs) – the youngest volcanic feature on the Moon, using hyperspectral data from Moon Mineralogy Mapper ($\rm{M}^{3}$) for the first time. Along with composition, the topographic and morphological mapping has been done to understand the possible evolutionary history of this mare. Total 22 spectral units has been identified based on Integrated Band Depth (IBD) parameter technique. Number of reflectance spectra were collected from the fresh craters of each spectral unit and quantitative mineralogical abundances estimated using band parameters like band centre, band strength and band area. The result shows abundances of olivine and pyroxene mixture bearing material in the mare basalt. The compositional map shows smaller spectral units in the western-low lying half and larger spatial distribution of spectral unit in the eastern half depicts probable large-scale volcanic eruption in the eastern part that may have Cowed to longer distances from the Cauchy shield to the central mare. This study marks 61 new domes in the Cauchy shield area and also depicts possible formation and evolutionary history of the Mare Tranquillitatis.

    • Integration of geophysics and petrography for identifying the aquifer and the rock type: A case study from Giddalur, Andhra Pradesh, India

      TAUFIQUE WARSI V SATISH KUMAR DEWASHISH KUMAR M J NANDAN GEORGE BISWAS DINESH KUMAR SAHADEVAN C MANIKYAMBA T VINODA RAO R RANGARAJAN SHAKEEL AHMED V CHANDRASEKHAR

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      A comprehensive geophysical and petrological study was carried out at Giddalur area in Prakasam district, Andhra Pradesh, which is geologically a highly deformed area and is difficult to delineate the aquifer zone(s). The task was to find out the exact rock type in which aquifer is concealed as well as to delineate the aquifer zone, which can yield sufficient quantity of water. The resistivity models derived from geophysical dataset were interpreted in terms of hydrogeology and the results revealed substantial resistivity contrast of the geological formations within the study area. We have delineated two major groundwater potential zones based on this study. These zones were tapped at different depths in diverse rock types. Drilled hand specimens (rock cuttings) were not adequate, so these specimens were petrographically studied to reveal the exact contact zones of the rock type. On integration of the geophysical and the petrographic results, it was illustrated that two aquifer zones were struck at a depth of 92 and 122 m between shale-phyllite and phyllite-quartzite, respectively. These findings were correlated, which matched with the lithology of the drilled borehole. This integrated approach will be helpful in strategy for groundwater assessment as well as prospecting groundwater resources in different geological terrain.

    • Eddy covariance measurements of $\rm{CO_{2}}$ exchange from agro-ecosystems located in subtropical (India) and boreal (Finland) climatic conditions

      PRAMIT KUMAR DEB BURMAN NARASINHA J SHURPALI SUBHARTHI CHOWDHURI ANANDAKUMAR KARIPOT SUPRIYO CHAKRABORTY SAARA E LIND PERTTI J MARTIKAINEN SEETHALA CHELLAPPAN ANTTI AROLA YOGESH K TIWARI P MURUGAVEL DINESH GURNULE KIRAN TODEKAR THARA V PRABHA

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      Climate impacts agriculture in various complex ways at different levels and scales depending on the local natural crop growth limitations. Our objective in this study, therefore, is to understand how different is the atmosphere–biosphere exchange of $\rm{CO_{2}}$ under contrasting subtropical and boreal agricultural (an oilseed crop and a bioenergy crop, respectively) climates. The oilseed crop in subtropical climate continued to uptake $\rm{CO_{2}}$ from the atmosphere throughout the year, with maximum uptake occurring in the monsoon season, and drastically reduced uptake during drought. The boreal ecosystem, on the other hand, was a sustained, small source of $\rm{CO_{2}}$ to the atmosphere during the snow-covered winter season. Higher rates of $\rm{CO_{2}}$ uptake were observed owing to greater day-length in the growing season in the boreal ecosystem.The optimal temperature for photosynthesis by the subtropical ecosystem was close to the regional normal mean temperature. An enhanced photosynthetic response to the incident radiation was found for the boreal ecosystem implying the bioenergy crop to be more efficient than the oilseed crop in utilizing the available light. This comparison of the $\rm{CO_{2}}$ exchange patterns will help strategising the carbon management under different climatic conditions.

    • Spatio-temporal analysis and forecasting of drought in the plains of northwestern Algeria using the standardized precipitation index

      KENZA ACHOUR MOHAMED MEDDI AYOUB ZEROUAL SENNA BOUABDELLI PAMELA MACCIONI TOMMASO MORAMARCO

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      Drought is the most frequent natural disaster in Algeria during the last century, with a severity ranging over the territory and causing enormous damages to agriculture and economy, especially in the northwest region of Algeria. The above issue motivated this study, which is aimed to analyse and predict droughts using the Standardized Precipitation Index (SPI). The analysis is based on monthly rainfall data collected during the period from 1960 to 2010 in seven plains located in the north-western Algeria. While a drought forecast with 2 months lead-time is addressed using an artificial neural network (ANN) model. Based on SPI values at different time scales (3-, 6-, 9-, and 12-months), the seven plains of north-western Algeria are severely affected by drought, conversely of the eastern part of the country, wherein droughtphenomena are decreased in both duration and severity. The analysis also shows that the drought frequency changes according to the time scale. Moreover, the temporal analysis, without considering the autocorrelation effect on change point and monotonic trends of SPI series, depicts a negative trend with asynchronous in change-point timing. However, this becomes less significant at 3 and 6 months’ time scales if time series are modelled using the corrected and unbiased trend-free-pre-whitening (TFPWcu) approach. As regards the ANN-based drought forecast in the seven plains with 2 months of lead time, the multi-layer perceptron networks architecture with Levenberg–Marquardt calibration algorithm provides satisfactory results with the adjusted coefficient of determination ($R^{2}_{adj}$) higher than 0.81 and the rootmean- square-error (RMSE) and the mean absolute error (MAE) less than 0.41 and 0.23, respectively. Therefore, the proposed ANN-based drought forecast model can be conveniently adopted to establish with 2 months ahead adequate irrigation schedules in case of water stress and for optimizing agricultural production.

    • Nature of spatial heterogeneity of the coastal, marine ecoregions along the eastern coast of India

      MEGHA GUPTA SUBHRONIL MONDAL HINDOLITA CHAKRABORTY PUNARBASU CHAUDHURI

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      The global marine environment is highly heterogeneous although the nature of heterogeneity can vary spatially. In this study, the nature and extent of spatial heterogeneity of the coastal, marine ecoregions along the Central-Eastern and South-Eastern coast of India (parts of Andhra Pradesh, Pondicherry andTamil Nadu) was studied, which represent two different – Central-Eastern, and South-Eastern – coastal ecoregions. Several environmental (e.g., salinity, temperature, and nutrients of the ocean water, etc.) and physical (e.g., substrate type, energy condition of the coast) parameters were measured (quantitative aswell as semi-quantitative approach) and analysed by using several bivariate and multivariate methods. Our results clearly point out that the Central-Eastern, and South-Eastern marine, coastal ecoregions of India are highly heterogeneous among themselves, and even smaller ecoregions (i.e., sub-ecoregions)within each of these larger ecoregions are also different from each other. Thus, each of these ecoregions is internally highly heterogeneous. In addition, there is no consistent spatio-latitudinal change in the environmental variables along the eastern coast of India.

    • Forecasting extreme precipitation event over Munsiyari (Uttarakhand) using 3DVAR data assimilation in mesoscale model

      N NARASIMHA RAO M S SHEKHAR G P SINGH

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      A localized extreme precipitation event occurred over Munsiyari (Uttarakhand, India) on 2nd July 2018 causing Cash floods, landslides and damage to the hydropower project. A preliminary study has been carried out by using Weather Research and Forecasting (WRF) model with three-dimensional variation data assimilation technique (3DVAR) to examine the feasibility of the model to predict the localized phenomena. Sensitivity experiments were carried out with two different microphysics in the model. Results show that P3 1-category plus double moment cloud water microphysics scheme with 3DVAR in WRF simulates the quantity of precipitation closer to the observed precipitation over Munsiyari. The vertical velocity and relative humidity were also simulated well during 3DVAR data assimilation as compared to without data assimilation over study region.

    • Composition of the peninsular India rivers average clay (PIRAC): A reference sediment composition for the upper crust from peninsular India

      SHAIK SAI BABU RAVIPATI VENKATA RAMANA VENIGALLA PURNACHANDRA RAO MEKALA RAM MOHAN ARADHI KESHAV KRISHNA SARIPOOT SAWANT NANNAPANENI SATYASREE

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      We present a new dataset on the average composition of the clay fraction of sediments in 13 rivers draining the entire peninsular India, referred to here as Peninsular India Rivers Average Clay (PIRAC). PIRAC showed relatively low Si and high Fe, Mn and Mg compared to the other reference sediments. The total trace elements ($\Sigma$TE) content of PIRAC was lower than that of Post-Archean average Australian Shale (PAAS), but close to that of Average Suspended Sediment of World Rivers (ASSWR). The total rare earth elements ($\Sigma$REE) content of PIRAC was slightly lower than that of PAAS but close to that of World River Average Clay (WRAC). The $\Sigma$TE and $\Sigma$REE were much higher for PIRAC than in other reference sediments. Anomalously high Cu, Zn and Pb in PIRAC suggest that these trace elements do not reliably indicate the crustal composition. PAAS-normalised REE of PIRAC showed LREE-depleted, MREE- and HREE-enriched REE patterns with positive Ce and Eu anomalies, suggesting that PIRAC is more mafic than that of PAAS and the clays weathered from volcanic rocks and felsic component of the metamorphic rocks dominated the crustal composition of peninsular India. The REE pattern of PIRAC resembles to that of European Shale (ES) and Mud of Queensland (MUQ) but different from PAAS, WRAC, upper continental crust (UCC) and East China Post-Archean Shale (ECPAS), which exhibit LREE-enriched and HREE-depleted REE patterns. It implies that the REE composition of the upper crust is not uniform and it should be thoroughly investigated to determine the composition of PIRAC with more analyses on sediments for better understanding of the evolution of the crust.

    • Study of solar cycle dependence of the quasi-two-day wave in the MLT from an extratropical station

      A GUHARAY P P BATISTA V F ANDRIOLI

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      The relationship between the quasi-two-day wave (QTDW) and solar variability during summer in the MLT is studied using long-term meteor wind observations from an extratropical station, Cachoeira Paulista ($22.7^{0}\rm{S}, 45^{0}\rm{W}$) in the Southern hemisphere. Overall, the seasonal (summer) mean and monthly mean zonal amplitude of the QTDW show a negative correlation and the meridional amplitude exhibits a positive correlation with the solar F10.7 flux in the MLT. Although the seasonal mean (summer) wave period shows positive correlation with the solar cycle, both positive and negative correlations are found in the monthly mean period in certain summer months at the present location. Additionally, both amplitude and period of the QTDW show slightly higher values in solar minimum and lower values in solar maximum within the limit of standard deviation indicating a weak, but measurable response to the solar cycle.The features of the present study bearing similarity as well as disagreement with the findings of the past investigators are also discussed in the perspective of current understanding.

    • Clay minerals from the Lameta Formation of Pandhari area, districts Amravati, Maharashtra and Betul, Madhya Pradesh: Its paleoclimatological implications

      ASHOK K SRIVASTAVA NEELAM K KANDWAL A KRISHNAKUMAR K ANOOP KRISHNAN

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      This report highlights the record of clay minerals from the Lameta Formation of a new locality of central India. A 9-m thick argillaceous column represented by various shades of grayish-greenish-brownish-yellowish coloured clay to silty-clay has been investigated. The clay has been separated from the host sediment by pipette method which has been further subjected to XRD analysis. The peaks identified are of palygorskite, sepiolite, illite, montmorillonite and kaolinite. The assemblage is interpreted to be a product of arid to semi-arid climatic condition due to weathering of pre-existing rocks. The depositional site also shows the possibility of short term marine incursion.

    • GIS based 3D visualization of subsurface geology and mapping of probable hydrocarbon locales, part of Cauvery Basin, India

      J SARAVANAVEL S M RAMASAMY K PALANIVEL C J KUMANAN

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      The hydrocarbon explorations were mostly guided by conventional geological and geophysical techniques in the past and modern tools like Remote Sensing, GIS, geophysical tomography came into being only during the last 2–3 decades. However, advanced virtues available with GIS, which could provide potential clues in deciphering the deep-seated natural resources were not capitalised deservingly. In this connection, the present article is the outcome of a study carried out in parts of Cauvery Basin, India for deciphering the subsurface hydrocarbon locales using Digital Elevation Modelling (DEM) techniques. The study was accomplished by the following hierarchical steps. (i) In the Brst step, DEM of gravity, litho tops depth of layered sedimentary rocks of Tertiary period and iso-resistivity data of 50 m depth were generated using Arc-GIS. (ii) It was followed by mapping the surface expressed circular features and the faults. (iii) Then, all the above surface and multi-depth data on the geological structures were integrated using Arc-GIS. (iv) From such an integration, 3D visualised domal structures of probable of hydrocarbon parentage were identified. (v) Finally, these were validated using known oil/gas wells. The study revealed the occurrence of domal structures with encircling peripheral faults from the subsurface to surface level in number of places. The spatial correlation of the known oil and gas occurrences with these 3D visualised domal structures indicated that the peripheral faults and domes have acted respectively as the zones of mobilisation and accumulation of oil and gas.

    • Linking variability of monsoon precipitation with satellite-based observations of stable water isotopes over Northeast India

      ROHIT PRADHAN NIMISHA SINGH RAGHAVENDRA P SINGH

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      Isotopic composition of atmospheric water vapor provides information on transport, mixing and phase change of water in the atmosphere. It provides a useful tool for understanding various aspects of the hydrological cycle. SCanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) onboard ENVISAT-1 was a spectrometer designed to measure the composition of trace gases in troposphere and stratosphere. It provided global measurements of total columnar HDO and $H_{2}O$ concentrations using the spectral window between 2338.5 and 2382.5 nm. Temporal variability of columnar $\delta\rm{D}$ was studied over Northeast (NE) India and mean columnar $\delta\rm{D}$ for pre-monsoon and monsoon months were correlated with precipitation data obtained from Global System for Mapping of Precipitation (GSMaP). It was observed that $\delta\rm{D}$ during the pre-monsoon months of April–May showed good correlation ($r$ > 0.7, $p$ < 0.05) with total precipitation during June–August for the corresponding year over forested regions of Meghalaya and parts of Assam. Analysis was also carried out to understand the relationship between SCIAMACHY derived gridded monthly $\delta\rm{D}$ and Multivariate El-Ni$\tilde{n}$o Index (MEI) with zero and one month lag periods. Positive correlation was observed between $\delta\rm{D}$ and MEI over parts of Central India, Myanmar and Thailand. Isotope ratio of water vapor provides additional information compared to traditional meteorological observations and holds the potential to improve forecasting models.

    • Characteristics of electromagnetic radiation signal of coal and rock under uniaxial compression and its Beld application

      XIAOFEI LIU ZHIBO ZHANG ENYUAN WANG XIAORAN WANG BO YANG HAO WANG

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      Rockburst is a serious threat to the safety and effciency of coal-mine production in China. Accurate monitoring and prediction of rockburst is an ongoing challenge in coal mining. Electromagnetic radiation (EMR) technology is a real-time and non-contact prediction method for changes in the mechanical parameters of coal or rock. In this paper, uniaxial compression testing of coal and rock samples was carried out, EMR data were collected and analysed from deformation to failure. The rescaled range ($R/S$) analysis method was applied to study the Hurst index of the EMR signals during the uniaxial compression test. The results showed that the higher the degree of deformation and failure, the larger the Hurst index. On the basis of the experimental and theoretical results, the Hurst index of the EMR signal during the ‘8.11’ rockburst in the Yuejin coal mine was analysed. The results showed that the Hurst index was low before the rockburst, and increased to 0.9 in the pre-rupture stage, then decreased 1–2 days before the rockburst. This suggests a correlation between EMR and the conditions leading to a rockburst event. Therefore, further study on the characteristics of EMR can contribute to development of early-warning technology for rockburst.

    • Application of neural network modelling for classifying hydrocarbon bearing zone, water bearing zone and shale with estimation of petrophysical parameters in Cauvery basin, India

      ATUL KUMAR PANDEY RIMA CHATTERJEE BISWAJIT CHOUDHURY

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      This work has been developed to classify sand and shale from seven wells in the Cauvery basin using a multilayered feedforward neural network (MLFN) model. Seven wells distributed over $5100 \rm{km}^{2}$ of this basin have been utilized for analysis of conventional well logs and reservoir characterization. Hydrocarbon bearing sediments of Andimadam, Bhuvanagiri, Nannilam and Niravi formations of the Cauvery basin are evaluated in terms of shaliness, cementation factor, porosity, water saturation, and permeability. Pickett plot has been applied to investigate the cementation factor, formation water resistivity, permeability. The cementation factor ($m$) varies from 1.31 to 1.86 in these formations, whereas permeability varies from 0.01 to 400 md. Very good quality reservoir exists in the Bhuvanagiri formation with high permeability 300–400 md, whereas a good quality reservoir is occurring in Niravi, Nannilam and Andimadam formations with hydrocarbon saturation 60–70%.

    • Subduction–collision processes and crustal growth in eastern Dharwar Craton: Evidence from petrochemical studies of Hyderabad granites

      ARIJIT PAHARI P PRASANTH DEVLEENA M TIWARI C MANIKYAMBA K S V SUBRAMANYAM

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      The granite batholiths of eastern Dharwar Craton, which are showing intrusive relationship with TTGs, exposed in the eastern part of Telangana state at University of Hyderabad, Gachibowli ($9.30 \rm{km}^{2}$), are studied for their petrographic and geochemical characteristics compared with their counterparts in EDC and evaluated their petrogenesis. These are predominantly microcline and quartz with subordinate plagioclase, exhibiting intergranular and perthitic textures. Geochemically, they are strongly peraluminous to slightly metaluminous in nature with high Alumina Saturation Index (ASI) ranging from 0.86 to 1.11 indicating the role of plagioclase in their genesis. Their alkali-calcic to alkalic nature, narrow range of Modified Alkali-Lime Index ($\rm{MALI; Na_{2}O+K_{2}O -CaO}$), and low Fe-number reflect their similarities with the I-type Cordilleran granites. Prominent negative Europium anomalies, high Sr, Rb, Rb/Sr and low Sr/Y ratios indicate moderate to low pressure partial melting of pre-existing TTG with residual plagioclase in the source. We suggest, the melting of older TTGs through crustal anataxis process formed these granites and the sanukitoid melts supplied the required heat for the melting of TTG to evolve into granites. The genesis of these granites supports reworking of older crust, crustal differentiation during syn-collisional stage and marks the stabilization of continental crust in the Dharwar Craton during the Neoarchean time.

    • Modelling of earthquake locations and source parameters in Kachchh region to understand genesis of earthquakes

      BHOOPENDRA SINGH PRANTIK MANDAL

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      Modelling of earthquake source locations and parameters infers seismogenesis of earthquakes. In this study, we modelled the earthquake source locations through hypocenter location algorithm using the difference in arrival time of P and S waves and source parameters through the Levenberg–Marquardt nonlinear inversion method using S-wave spectra. A total of 340 aftershocks of 2001 Bhuj mainshock (1.8$\leq M_{w}$ <4.3), which have occurred in Kachchh, Gujarat, India from January 2014 to January 2015, are located in this study. Out of 340 aftershocks, digital waveforms of 78 aftershocks (2.2$\leq M_{w}$ <3.9) are used for estimation of the earthquake source parameters. The results obtained from earthquake locations show two clusters of seismicity along the Kachchh Mainland Fault (KMF) and North Wagad Fault (NWF) and three felt events ($M_{w} =\geq 3.0$); one along the Katrol Hill Fault (KHF) ($M_{w} = 3.3$), two along the Banni Fault (BF) ($M_{w} = 3.0; 3.2$). The generation of these three felt events is attributed to the triggering mechanisms caused by the migration of Cuids or the stress pulse generated by the 20 MPa stress drop of the $M_{w} 7.7$ Bhuj earthquake. A marked concentration of events is noticed in 15–30 km depth range, which could be attributed to the presence of a mafic intrusive body, resulting in stress build-up for earthquake generation in this region. The results of source parameters; seismic moment ($M_{0}$), source radius ($r$) and stress drop ($\Delta\sigma$) vary from $1.86 \times 10^{12} \rm{to 3.2 \times 10^{15} N m}$, 146–262 m and 0.04–5.73 MPa, respectively. The maximum stress drop value is estimated to be 5.73 MPa at 24 km depth for the largest studied event of $M_{w} 3.9$. Large stress drops are confined to the 8–33 km depth range, which indicates the probable existence of the base of the seismogenic layer in this depth range. This observed large stress drops could be attributed to stresses induced by crustal maBc intrusive bodies and the presence of aqueous fluids in the lower crust below the region.

    • Susceptibility assessment of rainfall induced debris flow zones in Ladakh–Nubra region, Indian Himalaya

      H S NEGI ANANT KUMAR N NARASIMHA RAO N K THAKUR M S SHEKHAR SNEHMANI

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      In recent past, rainfall-induced debris flow events in Ladakh–Nubra region have caused loss of lives and damages to civil infrastructures and army locations. Therefore, there is a need of high spatial and temporal monitoring of precipitation, and further to assess susceptible rainfall-induced debris flow zones in the area. We assessed the rainfall data collected at two gauge stations and observed a significant increase in the rainfall amount over the study region during summer-monsoonal period 1997–2017. Increasing trend was also observed from CRU gridded precipitation dataset. A GIS-based multi-criteria evaluation (MCE) method was performed by combining topographical, environmental and hydrological parameters for mapping of rainfall-induced susceptible zones. Suitability analysis of precipitation forecasts from WRF model at higher resolution (3 km) was also performed. A good agreement (r = 0.76) was observed between 4-day model forecast and field observed rainfall. Further, the simulated precipitation from WRF was incorporated into GIS model for assessment of debris flow susceptible zones for two cases of heavy precipitation events. The modelled high, medium, low and very low risk susceptible zones identified for the year 2015 events are validated with field survey and pre-post satellite imageries, and found in good agreement (ROC = 76.6%). The model was able to identify affected areas during the Leh cloud burst event in year 2010. In addition, a threshold value of rainfall for initiation of debris flow in the region was also reported.

    • Elucidating intra-seasonal characteristics of Indian summer monsoon. Part-I: Viewed from remote sensing observations, reanalysis and model datasets

      DIPAK K SAHU T N KRISHNAMURTI VINAY KUMAR

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      In this study, we examine the transitions in the monsoon phases (onset, active, break and the withdrawal) during an entire monsoon season. This makes use of a host of observational tools that come from GPM (Global Precipitation Measurement) and TRMM (Tropical Rainfall Measuring Mission) satellites for precipitation estimates, the vertical structure of rain, hydrometeors and cloud types from TRMM and CloudSat datasets. During onset, the mean moisture convergence, especially over west and south-west coast of India is $2 \times 10^{-4} \rm{kg m^{-1} s^{-1}}$; however, it carries much higher value of >$4 \times 10^{-4 }\rm{kg m^{-1} s^{-1}}$ during the active phase over central eastern India. Much lesser moisture convergence (<$1 \times 10^{-4} \rm{kg m^{-1} s^{-1}}$) is noted over Western Ghats area during the break phase. However, there are northeasterly moisture fluxes present over southern part of India during withdrawal phase. The tall cumulonimbus clouds that extend out to 16 km are illustrate during onset, the active phase is dominated by alto stratus and nimbostratus type clouds that are somewhat shallower. In general, we noted an absence of such clouds during the break and the withdrawal phases. Those structures were consistent in a number of derived fields such as the moisture convergence, moisture fluxes, the energy conversions between the rotational and the divergent kinetic energy and the corresponding phases of the intra-seasonal oscillations.

    • Crustal architecture and rift tectonics across the Visakhapatnam Bay basin, central-east Indian margin: Insights from multichannel seismic and potential field data

      PRANAYA SANGVAI G SRINIVASA RAO K S R MURTHY M RADHAKRISHNA

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      The Visakhapatnam Bay (VB) basin is a passive margin rift basin located at the non-basinal segment of the Eastern Continental Margin of India (ECMI) and formed during the rift–drift events associated with the breakup of eastern Gondwanaland. In the present study, integrated analysis of potential field and multi-channel seismic reflection (MCS) data were carried out to understand the rift tectonics, crustal configuration and onshore–offshore structural continuity across this basin. The study revealed the following: (i) crustal models derived through joint gravity-magnetic modelling show limited stretching with 36–40 thick crust below the Eastern Ghat Mobile Belt (EGMB) thinning down to 16–20 km at the Ocean Continent Transition (OCT), (ii) extension of Charnockitic basement associated with the Eastern Ghat Mobile Belt (EGMB) into the offshore region. Comparison of the crustal configuration across the VB basin with that across the adjacent thick sedimentary area of the Krishna–Godavari shows that upper crustal configuration is significantly different in the VB area. The observed limited rift related structuration (horst-graben morphology), the mapped high angle break-away fault with large offset in the seismic data and narrow width (70–90 km) of extended crustal domain in VB basin suggests that this segment acts as transfer zone between Krishna–Godavari and Mahanadi rift zones. Further, long curvelinear trend of magnetic anomalies associated with Pudimadaka Lineament (PKL) demarcate the VB basin from the adjacent Krishna–Godavari rift zone.

    • Seismic imaging of subsurface geological structures by Kirchhoff’s migration based on extended Born approximation

      ALOK KUMAR ROUTA P R MOHANTY

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      Complex seismic signatures are generated because of the multifaceted nature of the subsurface. These features make the interpretation very complex. To understand the seismic behaviour, different numerical tools are available. In this present study, an attempt has been made to demonstrate both the modelling and imaging aspects of these complex subsurface features commonly encountered in petroleum exploration. The present work is an extended form of the Born approximation by using Green’s function based asymptotic ray theory. Subsequently, Kirchhoff’s depth migration has been applied to generate seismic shot gathers over structural as well as stratigraphic traps. From this analysis, it is observed that the technique is able to efficiently migrate both the structural and stratigraphic traps. The proposed technique also intends to handle strong velocity variation and amplitude restoration. However, some noise in terms of over-critical reflection has been observed in the depth migrated section corresponding to pinch-out and unconformity respectively.

    • Geochemistry of ultramafic–mafic rocks of Mesoarchean Sargur Group, western Dharwar craton, India: Implications for their petrogenesis and tectonic setting

      KIRANMALA PATRA R ANAND S BALAKRISHNAN JITENDRA K DASH

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      The Nuggihalli and Holenarsipur greenstone belts of the western Dharwar craton expose ultramafic–mafic rocks of the Mesoarchean. The rocks in these belts are geochemically considered as komatiites and komatiitic basalts with minor occurrences of tholeiitic and calc-alkaline basalts. The dominant ultramaficrocks of the Nuggihalli greenstone belt are layered and indicate fractionation processes at relatively shallower crustal levels. The Al-undepleted and Al-depleted signatures obtained could be attributed to magmatic differentiation processes and might be due to fractional crystallization of minerals such as hornblende and plagioclase, in addition to cumulus olivine and pyroxene. The chemical heterogeneity in the rocks of these greenstone belts might have therefore developed during the intrusion of the parental melts and their differentiation into a layered igneous complex. The differences in the lithological characteristics of the Holenarsipur and Nuggihalli greenstone belts can be explained by their different crustal levels of exposure. Presence of spinifex-textured komatiites need not necessarily imply that the sources have to be ultramafic and therefore of a deeper origin. This study indicates that the parental melts for unambiguous layered intrusive ultramafic–mafic complexes could be high-Mg basalts originating from relatively shallower levels. The probable geodynamic setting for the emplacement of the rocks of the two greenstone belts could be in a plume-modified mid-ocean ridge that was too thick and buoyant to be subducted, and the decompression-melted magma chamber developed igneous layering as the magma stalled in the lithosphere.

    • Suitability of distributions for standard precipitation and evapotranspiration index over meteorologically homogeneous zones of India

      N T MONISH S REHANA

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      The Standardised Precipitation and Evapotranspiration Index (SPEI) became one of the popular drought indices in the context of increasing temperatures under global warming in recent periods. The SPEI is estimated by fitting a probability distribution for the difference between precipitation (P) and potential evapotranspiration (PET), which represents the climatic water balance. The choice of an inappropriate probability distribution may lead to bias in the index values leading to distorted drought severity. Till date, none of the studies have focused on the suitability of the probability distribution for SPEI over India. The objective of the present study is to compare and evaluate the performance of a group of candidate probability distributions over seven meteorologically homogeneous zones and all over India using high resolution ($0.25^{0}$) gridded daily precipitation data from India Meteorological Department (IMD). The Kolmogorov–Smirnov (K–S) test was used to test the goodness-of-fit for (P–PET) and Akaike Information Criterion (AIC) was used to obtain the relative distribution rankings for each grid point. The results of the study suggest that Pearson type III distribution has performed better than other distributions, significantly for shorter time scales and slightly for longer time scales, for each meteorological homogeneous zone based on K–S test. Also, for shorter time scales, Pearson type III distribution has been observed to be significantly better based on AIC with 82.89% and 71.91% grid points for 3 and 6 months, respectively. However, the relative ranking by AIC revealed GEV distribution as the best fit for SPEI values all over India for longer time scales with total grid points as 50.26%, and 58.81% for 12- and 24-month time scales respectively. Pearson type III distribution for shorter time scales (3 and 6 months) and GEV distribution for longer time scales (12 and 24 months) have been identified as the best distributions for fitting SPEI for Indian case study. Comparison of GEV based SPEI with remote sensing-based drought severity index (DSI) for drought events indicated concordance for most of regions in India. Also, SPEI is evaluated to test its capability to represent seasonality and its performance has been compared with Standardised Precipitation Anomaly Index (SPAI) which is known to represent seasonality well.

    • Spatial-temporal changes in NPP and its relationship with climate factors based on sensitivity analysis in the Shiyang River Basin

      XUELEI ZHANG WEIHUA XIAO YICHENG WANG YAN WANG HEJIA WANG YAXU WANG LISHAN ZHU RUIXIANG YANG

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      As a typical inland river basin in China, the Shiyang River Basin is characterized by its special mountain-basin structure. The ecological health in the basin is related to the sustainable development of the economy and society. At present, there are few studies on net primary productivity ($NPP$) in the Shiyang River Basin, and the existing analysis of the relationship between $NPP$ and climatic factors is lacking. The upper mountainous area and the middle and lower oasis areas in the Shiyang River Basin were selected as the study area. The $NPP$ of the study area was estimated using the Thornthwaite Memorial Model. The spatial and temporal characteristics of $NPP$ were analyzed by Sen’s slope method. Based on the sensitivity analysis, the correlation of the main climate factors to $NPP$ was estimated. According to the aforementioned work, the variation trend of the future $NPP$ was predicted. The results showed that $NPP$ in the study area increased from 1981 to 2015 with the increase in temperature and precipitation. The spatial heterogeneity of the change trend of $NPP$ was not significant, but the spatial heterogeneity of the rangeability was strong. The $NPP$ was highly sensitive to precipitation, relative humidity and net solar radiation. By integrating the changes in climatic elements, the temperature, precipitation and relative humidity contributed the main parts of the change in $NPP$. The $NPP$ is predicted to increase by 4.9–8.1% by 2050 according to the amplitude of climate change over the past 35 yrs.

    • Role of colloid in metal transport in river water around Jaduguda uranium mines, Singhbhum shear zone

      SK MD EQUEENUDDIN SHAHEEN AKHTAR FAKIRA BASTIA SUBHRANSU SEKHAR ROUT PALLAV JYOTI SAIKIA

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      This paper attempts to identify and characterize the colloids present in the river water around the Jaduguda uranium mines located in Jharkhand, India in order to understand their role in metal transport. The stream receiving direct release of effluent water from the mine tailing is contaminated and the concentration of $\rm{Mn, F^{-}, Na^{+}, SO_{4}^{2-}}$ and $\rm{U}$ is above the maximum permissible. The colloids mostly consist of Mn-oxide, kaolinite, halloysite and Fe(oxy)hydroixe. The concentration of As, Co, Cu, Mn, Ni, Pb, U and Zn in surface water is very much lower than that of the colloids. This is attributed to the importance of colloids in metal scavenging due to more reactive surface sites. The high resolution transmission electron microscope (HRTEM) study further indicates that Mn-oxides plays a most important role in retention and transportation of U in the study area.

    • Gondwana biostratigraphy and geology of West Bengal Basin, and its correlation with adjoining Gondwana basins of India and western Bangladesh

      BIJAI PRASAD B S PUNDIR

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      Integrated biostratigraphic and geological studies on the drilled exploratory boreholes of West Bengal Basin have revealed the presence of very thick distinctive Permo-Triassic Gondwana successions in the subsurface, and widely recognized across the basin below the latest Jurassic–Early Cretaceous Rajmahal Traps. Precise geological age of identified Gondwana lithounits of this basin is inferred on the basis of associated palynofloral assemblages along with their correlation with the adjoining Gondwana basins. In addition, two Gondwanic grabens are recognized below the pericratonic set-up whose presence in this basin, till now, are poorly understood. Detailed palynological studies on the Gondwana successions in thekey boreholes of this basin enable recognition of 12 established palynological zones ranging from Early Permian (Asselian) to Middle Triassic (Ladinian). Lower Gondwana (Permian) palynofloras of this basin resemble earlier recorded palynofloras from the Talchir, Barakar and Raniganj formations of Indian Gondwana basins, suggesting the occurrence of well-developed above Lower Gondwana lithounits in this basin and the absence of Karharbari and Barren Measures formations which are marked by the nondepositional hiatuses. Upper Gondwana successions (Triassic) of the basin are represented by the Early and Middle Triassic palynofloras only that resemble Panchet and Supra-Panchet (Molangdighi Formation) palynofloral assemblages, and indicate the absence of Late Triassic succession of Upper Gondwana. Newly acquired geological and Bouguer anomaly data, and spatial distribution of Gondwana bearing boreholes across the basin suggest that the boreholes of CHK-A, GB-A, HRP-A, AMD-A, PLS-A and MNG-A fall in a well-defined NNE–SSW aligned graben, defined as the ‘Chandkuri–Palasi–Bogra Gondwanic Graben’ which includes Chandkuri and Palasi Gondwana basins in Indian part and Bogra Gondwana Basin in western Bangladesh where thick Gondwana successions are recognised in the subsurface sections of Singra (Singra-1X, Kuchma-X1, Bogra-X1), Jamalganj (EDH-1, 6) and Barapukuria (GDH-40, 43) coalBelds. Gondwana bearing boreholes in the western margins of West Bengal Basin (GLS-A, GLS-B, GLS-C) represent a quite separate Gondwana basin of ‘Galsi’ which is located in the southern part of the N–S trending ‘Purnea–Rajmahal–Galsi Gondwanic Graben’. Latest Jurassic–Early Cretaceous Rajmahal Traps cap the Gondwana successions in the above Gondwana basins of West Bengal Basin along with Bogra and Rajmahal Gondwana basins. Rajmahal Traps and its infra- and intertrappean beds are exlcuded from the Gondwana cycle as these beds are marked by the Early Cretaceous marine dinoflagellate cysts, and the Rajmahal volcanism took place after a very long time gap from Late Triassic to Late Jurassic (ca. 78 my). Rajmahal Traps and its infra- and intertrappean beds indeed represent the post-Gondwana syn-rift sequence in West Bengal, Mahanadi and Rajmahal basins, and closely related with the break-up of Indian Plate from the East Gondwanaland during Tithonian (ca. 150 Ma). The post-trappean Late Cretaceous successions mark the initiation of passive-margin phase in this basin with the deposition of marine Bolpur and Ghatal formations.

    • Active rifting and bimodal volcanism in Proterozoic Papaghni sub-basin, Cuddapah basin (Andhra Pradesh), India

      SUKANTA GOSWAMI SUKANTA DEY SYED ZAKAULLA M B VERMA

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      Bimodal volcanism in the Cuddapah basin is associated with a cratonic rift setting. The Cuddapah basin consists of five sub-basins (viz., Papaghni, Nallamalai, Srisailam, Kurnool and Palnad) and a total thickness of $\sim$12 km sediments and associated bimodal volcanics. The oval-shaped gravity high observed over the Papaghni sub-basin is due to lopolithic intrusions along listric faults. A basin evolution model is prepared in this context with signatures of active rifting.Mapping and geochemical sampling along the Tadpatri–Tonduru tract along with petrographic observations additionally supports the proposed model. The model presents the mechanism of bimodal volcanism during rifting and sedimentation. Basin evolution with tectonic modifications revealed a link with global tectonic events (e.g., $\sim$1.8 Ga Hudsonian orogeny, $\sim$1.3 Ga Grenville orogeny, $\sim$0.9 Ga Enderbia docking). The stratigraphic disposition of the surge, flow, fall and volcaniclastic deposits in this old Proterozoic terrane indicate the magma history and eruption conditions. The felsic volcanic rocks are classified as rhyolite and rhyodacite. The mafic volcanics are mainly basaltic. Primordial mantle normalized trace element plots indicate enrichment of large ion lithophile elements (Rb, Th and K) along with negative Sr, P and Ti anomalies. The chondrite normalized REE patterns are characterized by LREE enrichment, negative Eu anomaly and flat HREE pattern. These features indicate origin of felsic volcanics through shallow crustal melting with plagioclase either as a residual or a fractionating phase. The mafic rocks of the area are product of shallow mantle melting related to asthenospheric upwelling followed by decompression melting and generation of basaltic magma. This was also associated with lithosphereic stretching, rifting and initiation of sedimentation. The less viscous mafic magma was probably channelized along the rift-related faults. The underplating and intraplating of hot mantle-derived magma supplied heat into the crust. The attendant partial melting of continental crust produced the felsic magma. Different sub-basins within the Cuddapah basin indicates a combined mechanism of rifting and orogenic events.

    • Assessment of water resources and crop yield under future climate scenarios: A case study in a Warangal district of Telangana, India

      TIRUPATHI CHANAPATHI SHASHIDHAR THATIKONDA VENKATA REDDY KEESARA NAGA SOWJANYA PONGURU

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      In the present study, assessment of the impact of climate change on the availability of water resources and crop yield of Warangal district of Telangana state, India has been carried out using Soil and Water Assessment Tool (SWAT). The importance of bias correction methods in regional forecasts with multiple Regional Climate Models (RCMs) along with projected uncertainties have been emphasized, and regionalization of parameters in ungauged watersheds have been dealt with. SWAT model was run using observed data and then calibrated using observed streamflow of Akeru watershed, Warangal district, India. The R2 and NSE values for calibration (0.72 and 0.84, respectively) and validation periods (0.7 and 0.56, respectively) indicated a significant correlation between observed and simulated streamflow. Thenthe model was run for historical and future scenarios (early, mid, and end of the 21st century) for four RCMs. Variables such as rainfall, surface runoff, water yield, evapotranspiration, and intensity of rainfall showed an increasing trend under future scenarios, while crop yields (corn, cotton and rice) showed adecreasing trend. The models predicted an increase in the extremity of rainfall events, especially in the months of July and August, for the mid and end of the 21st century. The results showed that the production of cotton is under threat in the district in future. The results obtained can be used to plan the mitigation and adaptation strategies for the region.

    • Evidence for glacial deposits during the Little Ice Age in Ny-Alesund, western Spitsbergen

      ZHONGKANG YANG WENQING YANG LINXI YUAN YUHONG WANG LIGUANG SUN

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      The glaciers act as an important proxy of climate changes; however, little is known about the glacial activities in Ny-Alesund during the Little Ice Age (LIA). In the present study, we studied a 118-cm-high palaeo-notch sediment profile YN in Ny-Alesund which is divided into three units: upper unit (0–10 cm), middle unit (10–70 cm) and lower unit (70–118 cm). The middle unit contains many gravels and lacks regular lamination, and most of the gravels have striations and extrusion pits on the surface. The middle unit has the grain size characteristics and origin of organic matter distinct from other units, and it is likely the glacial till. The LIA in Svalbard took place between 1500 and 1900 AD, the middle unit is deposited between 2219 yr BP and AD 1900, and thus the middle unit is most likely caused by glacier advance during the LIA. Glaciers during the LIA likely overran the sampling site, removed part of the pre-existing sediments, and contributed to the formation of diamicton in the middle unit. This study provides evidence for glacial deposits during the LIA in Ny-Alesund and improves our understanding about historical glacier dynamics and ice-sheet margins during the LIA in western Spitsbergen.

    • Investigation of sources of atmospheric dust in Guiyang City, southwest China using rare earth element patterns

      YANG TANG GUILIN HAN

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      Rare earth elements (REE) of atmospheric dust were used in many investigations to trace the potential sources of environmental materials. In this study, we collected atmospheric dry deposition samples monthly from May of 2009 to January of 2011 over one and half year in a typical karst urban area of Guiyang city, southwest China, and measured the contents of REE to trace the sources. The total REE contents ($\Sigma$REE) of the dusts ranged from $\rm{9.48 to 181 mg kg^{-1}}$, with an average of $\rm{93.9 mg kg^{-1}}$. The $\Sigma$REE content of atmospheric dusts is similar to the contents of local soils. All the dust samples showed slighter Ce and Eu anomalies, and the dusts deposited in dry season showed slightly positive Ce anomaly. PAAS (post-Archean Australian shale) normalized REE patterns showed that there was significant difference between the dusts of dry seasons and wet seasons. The values of PAAS-normalized $La_{N}/Yb_{N}$, $La_{N}/Sm_{N}$ and $Gd_{N}/Yb_{N}$ of atmospheric dusts were closer to those of local soils collected in dry seasons, whereas the REE characteristics and patterns of dusts were similar to anthropogenic urban air particulates in wet seasons, demonstrating that dusts weremainly originated from anthropogenic inputs.

    • Forming topography in granulite terrains: Evaluating the role of chemical weathering

      ASMITA MAITRA ADITI CHATTERJEE TIRUMALESH KEESARI SAIBAL GUPTA

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      Granulite terrains have gently undulating topography, with charnockites and khondalites forming hillocks within low-lying areas comprising quartzofeldspathic gneisses (QFG). Petrographic, XRD and spectroscopic studies reveal that QFGs and charnockites show minimal clay mineral formation, indicating their resistance to chemical weathering. In contrast, khondalites weather progressively to form a variety of clay minerals, the proportion of which increases with elevation, ultimately stabilizing bauxite on hilltops. Geochemical modelling indicates that this weathering pattern in khondalites can develop under open system conditions prevailing on hill tops and slopes, as rainwater is not retained within the system. This implies that the khondalite hills existed before bauxite formation. Since khondalite hills occur within more resistant but low-lying QFG, the present granulite terrain topography was not shaped by chemical weathering. Rather, mechanical weathering or neo-tectonic activity may be responsible for topography formation in stable granulite terrains.

    • RedeBning the timing of Tongul glacial stage in the Suru valley, NW Himalaya, India: New insights from luminescence dating

      S NAWAZ ALI P MORTHEKAI SHACHI BAJPAI BINITA PHARTIYAL ANUPAM SHARMA M FIROZE QUAMAR SIDDHARTH PRIZOMWALA

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      The present study investigates latero-frontal moraines to reconstruct the pattern of glacier advances and associated climate variability in the Suru valley, southwestern Zanskar Himalaya. Impressive sets of latero-frontal moraines and discontinuous morainic ridges (recessional) represent the records of the past glacier advance and retreat. The northerly trending latero-frontal moraines that descend down the tributary valleys and terminate at the trunk Suru valley are the geomorphic expression of one of the oldest preserved record of glacier advance and is named as Tongul glacial stage. Previous studies (based on $^{10}\rm{Be}$ and $^{14}\rm{C}$ ages) deBning the chronology of Tongul glacial stage are either limited in number ($^{14}\rm{C}$ ages) or have a large spread ($^{10}\rm{Be}$ ages) and hence demand further investigation. Optically stimulated luminescence (OSL) dating suggests that the Tongul glacial stage responded to the global last glacial maximum (gLGM) dated between $\sim$ 20 and 24 ka. We suggest that the Tongul glacial stage was driven by enhanced mid-latitude westerlies and reduced temperature (viz., continental cooling) during MIS 2 andfacilitated by corresponding long winters.

    • The Palaeogene record of Himalayan erosion in the Andaman Basin

      NEERAJ AWASTHI JYOTIRANJAN S RAY

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      The Himalayan orogeny has been recognized as one of the most important Cenozoic events that shaped the geography, climate and ocean chemistry of our planet. The erosion in the Himalayas is believed to have played a critical role in crustal deformation and changes in the chemistry of the ocean water since the Eocene. In spite of the fact that the orogeny began after India–Asia collision at $59\pm1$ Ma, the record of its earliest erosional history is meagre. In an attempt to fill this gap in the knowledge, we studied temporal changes in provenance of Paleogene–Neogene siliciclastic sediments of the Andaman Islands, deposited in a trench-forearc basin in the Bay of Bengal. Using Sr-isotope stratigraphy and tephrochronology we determined the timings of depositions of various lithologies. Sediment sources were identified using trace element and isotopic (Sr–Nd) fingerprinting. Results of our study suggest that the Myanmar Arc had remained a constant sediment source to the Andaman basin during 55–5 Ma, whereas the basin started receivingsignificant continental sands input after 35 Ma that increased with time until $\sim$20 Ma. Geochemical provenance of these sands suggests their derivation from Precambrian crustal sources in the Himalaya, which probably is an outcome of higher erosional rates subsequent to a rapid exhumation of the orogen in the late Eocene and efficient sediment transport through the palaeo-channels of the rivers Brahmaputra and Ganga under optimal conditions of the Indian monsoon. Such a scenario is consistent with the idea that the Himalayan sediment input is the cause for the conspicuous rise in marine $^{87}\rm{Sr}/^{86}\rm{Sr}$ since $\sim$40 Ma. Our data also suggest that since the Miocene, sediment sources in the Indo-Burman Ranges and the Myanmar arc have become the major contributors to the Andaman Basin through the Irrawaddy river system.

    • Implication of weathering and mineral sorting on rare earth element geochemistry of Pleistocene–Holocene sediments from Cauvery delta, south India

      MALIK ZUBAIR AHMAD PRAMOD SINGH

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      REE analysis of sediments was carried out on representative samples from two cores drilled at Uttrangudi and Porayar locations from Cauvery delta in south India to better understand the patterns and textural and mineralogical control on REEs. Good correlation of REEs and their chondrite normalized ratios $\rm{(Gd/Yb and La/Yb)_{N}}$ with Ti, Th and Y in both the cores suggest control of Allanite, Titanite and Monazite among heavy minerals on the REE distribution in sediments. Good to strong positive correlation among REEs and Al, Fe, Mg, Ni, Cr, Sc and Co in both the cores suggests partial control of mafic minerals and clay. The Eu/Eu* values show a significant negative correlation with the CIA values, suggesting that the Eu in sediments has been modified to some extent by the process of weathering, affecting its loss and consequently lowering of Eu/Eu* values particularly in Uttrangudi sediments. The correlation of various trace elements with Eu/Eu* suggests that the enrichment of LREE bearing heavy minerals (Allanite, Titanite and Monazite) has resulted in relatively higher increase in LREE and HREE in comparison to Eu that is dominantly held in feldspars, which has further resulted in decreased value of Eu/Eu*.

    • Bias correction of maximum temperature forecasts over India during March–May 2017

      HARVIR SINGH ANUMEHA DUBE SUSHANT KUMAR RAGHAVENDRA ASHRIT

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      In recent times, instances of intense heat waves have increased over the Indian subcontinent. This increase in temperature has an adverse effect on human health and the economy. Over India, such high temperatures are usually seen during the months of March–May (summer). For weather forecasters, it is a challenging job to accurately predict the timing and intensity of this anomalous high temperature. The difficulty in the accurate prediction of weather is increased because of the presence of systematic biases inthe models. These biases are present because of improper parameterizations or model physics. For increasing the reliability or accuracy of a forecast it is essential to remove these biases by using a process called post-processing. In this study the biases in the surface temperature maximum are corrected using two methods, namely, the moving average and the decaying average. One of the main advantages of both the methods is that they do not require a large amount of past data for calibration and they take into account the most recent behaviour of the forecasting system. Verification, for maximum surface temperature during March–May 2017, was carried out in order to decide upon the method giving the best temperature forecast. It was found that both the bias correction methods lead to a decrease in the mean error in maximum surface temperature ($T_{max}$). However, the decaying average method showed a higher decrease in the mean error. Scores obtained from a contingency table like POD, FAR and PSS, showed that for $T_{max}$, the decaying average method outperforms the forecasts, i.e., raw and moving average in terms of having high POD and PSS and a low FAR.

    • Investigation of hydrologic inCuence of geologic lineaments in areas of the Lower Benue Trough, Southeastern Nigeria

      S N UKPAI C O OKOGBUE I A OHA

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      Stratigraphic formations, namely, Asu River, Ezeaku, Awgu and Nkporo Groups; belonging to Albian, Turonian, Coniacian and Campanian ages, respectively, underlie the studied region. The formations aredominated by groundwater problematic clastic sediments. This study is aimed at tracing fracture zones for groundwater prospects and delineating hydrological catchments for the watershed managementstrategy. It commenced with analyses of aeromagnetic and edge enhanced band 5 Landsat 7 ETM+ data, with application of Blters like reduction to equator (RTE), Brst vertical derivatives (1VD), total horizontal gradient (THG) and analytical signal. The THG of the RTE grids was combined with the edge enhanced Landsat data and utilized on-screen lineament discriminations. Results showed igneousintrusive representative lineaments in Asu River Group. Lineaments pinpointing ferruginous structures like ironstones stained the Nkporo Group. Further applications of edge enhanced Blters delineated lineaments as river beds, fractures/fault nodes and fold axes. The lineaments trending NW–SE depict fracture axes and river beds, whereas those trending NE–SW represent axial anticlines. Validation ofresults with electrical sounding veriBed the relevance of outcropping fractures as conduits through which groundwater discharges from the shallow water table at the northwestern hill range region; producingCuvial systems like river tributaries/catchments. Conversely, the rivers recharge the groundwater via fracture linking to deeper water table downstream.

    • Rainfall over the Himalayan foot-hill region: Present and future

      ARKADEB BANERJEE A P DIMRI KIREET KUMAR

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      Uttarakhand, one of the Himalayan foot-hill states of India, covers an area of $51,125 \rm{km}^{2}$. This region is enriched with bio-diversity and is one of the highly potential regions in the Central Himalayas for agroclimate, hydro power generation, food-processing, tourism, etc. Present study investigates the spatio-temporal rainfall distribution over the state during Indian summer monsoon period. Observational and modelled (under different Representative Concentration Pathways (RCPs) at radiative forcing 2.6, 4.5 and $8.5 \rm{W/m}^{2}$) rainfall distribution is studied to assess the present and future trends. Study uses standard observational rainfall estimates from APHRODITE, Tropical Rainfall Measuring Mission (TRMM 3B42) and India Meteorological Department (IMD) gridded rainfall datasets and inter-compare these products in order to Bnd out orographic responses during the monsoon months and elevation dependent mean rainfall pattern changes. It is found that rainfall pattern breaks near 3100 m elevation. Comparative analysis reflects that with respect to IMD, TRMM 3B42 rainfall underestimates more than 3 mm/day rainfall whereas, APHRODITE overestimates rainfall below 4.5 mm/day. Future trends in modelled monsoon rainfall are examined and mixed results are found and discussed with possible explanation.

    • Ecostratigraphic implications of a Late Palaeocene shallow-marine benthic community from the Jaintia Hills, Meghalaya, NE India

      SUMAN SARKAR

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      Moderately preserved shallow-marine extinct, fossil benthic community has been recovered from a sub-surface Late Palaeocene limestone cave section near Lumshnong in the Jaintia Hills, Meghalaya, NE India. The present contribution focuses on the ecostratigraphic implications of the carbonate microbiofaciesbased on the evaluated facies gradients. Precise field assessments and microscopic observations led to the identification of three microbiofacies: benthic foraminiferal–algal grainstone, coralline algal framestone and oolitic grainstone–packstone. The microbiofacies distinguished in the study suggest a general shallowing-upward trend from an inner shelf setting to a lagoonal–shoal environment depicting the distinct changes in the benthic community. Presence of coralline alga Distichoplax biserialis and benthic foraminifera Idalina sinjarica, Daviesina khatiyahi, Miscellanea primitiva, Rotalia trochidiformis and Vania anatolica assign the studied carbonates to Early Thanetian (SBZ 3) corresponding to the lower part of the Lakadong Limestone. In this study, ecostratigraphy has facilitated the classification of a single carbonate section corresponding to a solitary shallow benthic zone into multiple microbiofacies attributedto variable environmental depositional conditions. This clearly demonstrates its potential in improving the applicability of biostratigraphy worldwide.

    • Dimensionality analysis of MT data using Mohr circle: A case study from Rewa–Shahdol region, India

      KHASI RAJU PRASANTA K PATRO

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      Mohr circle in magnetotelluric (MT) is being used to represent dimensionality of subsurface structure. Mohr circle plot on individual axes for each frequency represents the dimensionality concerning frequency, whereas plotting of Mohr circle on common Cartesian coordinates for all frequencies displays the effects of noise on the impedance tensor. Here, we examine the Rewa–Shahdol region MT data with the Mohr circle approach to understand the sub-surface dimensionality structure, but the presence of noise in the signal has randomized the Mohr circle response. Hence, we made an effort to obtain the subsurface dimensionality using Mohr circle properties and derive two new invariants such as tan $\phi$ and sin $\phi$. The two invariants represent the dimensionality and anisotropy nature of the subsurface structure. Results from the Mohr circle together with the new angles brought out the 1-D graben structure of the Gondwana and Vindhyan basins, 2-D/3-D nature of the underlying basement structure and the crustal structure below the Narmada–Son Lineament (NSL) zone. 2-D/3-D nature of the NSL zone represents the basement uplifted horst structure between Gondwana and Vindhyan basins. Further, the horst-graben structure of NSL zone is evident from the Mohr circle analysis suggesting of rifting and block movement.

    • Multiparametric coupling and constrained interpolation to improve natural recharge estimation

      SUBASH CHANDRA BO HOLM JACOBSEN NIELS B CHRISTENSEN SHAKEEL AHMED SAURABH K VERMA

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      The inverse modelling technique seeks to improve the existing estimates of natural recharge in hard rocks by coupling multiple hydrogeophysical parameters that jointly affect natural hydrogeological processes. This approach involves coupling of an initial set of multiple hydrogeophysical (soil resistivity, bedrockdepth and rainfall) parameters in the form of exponents assigned to each parameter and a multiplication coefficient to obtain natural recharge. These model parameters (i.e., exponents and coefficients) are then quantified using linear least squares inversion against the known recharge values. To reduce the effect of geomorphic heterogeneity, viz., hills on natural recharge, laterally constrained inversion has been employed to integrate data sets (e.g., recharge measured at various points and logical expectation over exposed hills in an area) and constrained interpolation is then carried out along the grid lines for increaseddata density. Finally, Kriging interpolation over dense data obtained through data integration and constrained interpolation is used to significantly minimise the risks of overshooting the observations. Thus, the present approach provides a realistic spatial distribution of natural recharge values in a highly heterogeneous hard rock terrain.

    • Trajectories of three drifters deployed simultaneously in the northeastern Arabian Sea

      SHRIKANT DORA RAHUL KHEDEKAR S G APARNA

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      Three drifters were deployed in the northeastern Arabian Sea at ($69.18^{0}\rm{E}, 19.77^{0}\rm{N}$). They were released almost at the same time on 29 November 2016. The three drifters, initially moved poleward along the direction of the west India coastal current. The distance between any two drifters is less than 5 km for initial 8 days. The drifters veered apart when they moved along the edge of an anti-cyclonic or cyclonic circulating loop, thereby increasing the distance between them. Within a period of six months, the three drifters were in different directions and the distance between them was more than 600 km.

    • Crustal shear-wave velocity structure in Western Java, Indonesia from analysis of teleseismic receiver functions

      T ANGGONO S SYUHADA F FEBRIANI L HANDAYANI M M MUKTI A AMRAN

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      We analysed receiver functions from teleseismic events recorded at 11 broadband seismometers in the western part of Java Island, Indonesia. The stations are mostly located at three main geological environment including Northwest Java Basin, Bogor Zone, and Southern Mountains Arc. A total of about 341 receiver functions were computed using iterative time domain deconvolution. We derived shear-wave velocity structure and crustal $Vp/Vs$ ratio by inverting stacked radial receiver functions using non-linear neighbourhood algorithm. Inversion results show sediment thickness varies between 1 and 2 km thick in Western Java. Our inversion shows that crustal thickness in this region varies between 25 and 32 km. Average crustal $Vp/Vs$ ratio is estimated to be about 1.69–1.78. We hope the study may provide useful information for velocity model and crustal thickness for Indonesia region.

    • Thermal anomalies detection before Saravan earthquake (April 16th, 2013, $M_{W}$ = 7.8) using time series method, satellite, and meteorological data

      MARZIEH KHALILI SEYED SABEREH ABDOLLAHI ESKANDAR SEYED KAZEM ALAVI PANAH

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      Thermal anomaly detection related to strong earthquakes is one of the earthquake precursors extensively investigated by researchers. In this research, five years (March 16th to May 16th, every year from 2009 to 2013) of Land Surface Temperature (LST) data products, obtained from satellite data (MODIS-Aqua), and meteorological data (air and soil temperature), using three-dimensional time series method, have been analyzed to characterize the thermal anomalies related to the Saravan earthquake (April 16th, 2013, $M_{w}$ = 7.8). The results indicate that the thermal anomalies were observed in the time period before and after the earthquake. In the LST time–space–temperature coordinates, the thermal anomaly pattern was seen before the Saravan earthquake. In the Kriging surfaces of the air temperature and the difference between the LST and air temperature (DT), considerable changes were seen a few days before the earthquake until a few days after it. In addition, the soil temperature time–space–temperature coordinates show changes (increase) a few days after the Saravan earthquake. Therefore, the obtained results suggest that these changes (thermal anomalies) are related to the earthquake and can be expressed as an earthquake predictor.

    • Evolution of the hydraulic properties of deep fault zone under high water pressure

      ZIWEI QIAN ZHENQUAN JIANG YUNZHANG GUAN

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      Repeated water injection tests with varied injection flow rates are conducted on a fault zone under the roadway floor to study the evolution of the hydraulic properties of fault zone under high water pressure. Based on the analysis of test results, the evolution process of the hydraulic properties of fault zone under high water pressure can be divided into three successive stages: the initial infiltration stage, the splitting stage, and the scouring infiltration stage. It is found that in the splitting stage and the scouring infiltration stage, the hydraulic conductivity of fault zone increases rapidly under the condition of sufficient water supply, and this is likely to evolve into a large-flow-rate water inrush accident. Therefore, the safety factor e of fault zone should be defined as the ratio of the splitting pressure of fault zone $P_{f}$ over the aquifer pressure $P_{h}$, i.e., $e = P_{f} /P_{h}$; when e < 1, water inrush may occur in the fault. Based on the results in this study, a new method is proposed for assessing the risk of fault.

    • A new approach in calculating porosity of shallow unconsolidated soil based on Archie’s Law

      N ROSLI N A ISMAIL R SAAD N RAHMAN

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      Porosity ($\phi$) of soil/rock is frequently approximated using Archie’s Law where bulk resistivity ($\rho_{\rm{o}}$) is obtained from resistivity method while pore-fluid resistivity ($\rho_{\rm{w}}$) relies on well/borehole availability. This research proposes a new approach in obtaining $\phi$ of unconsolidated soil. The study was conducted at Balik Pulau, Minden and Teluk Kumbar. Clay’s presence was determined via particle size distribution (PSD) analysis. PSD graphs’ curves show that Balik Pulau is composed of elastic silt, while the other two sites consist of sand dominantly. For verification, soil samples’ porosities, $\phi_{\rm{sample}}$, were measured to produce 31.93, 32.95 and 26.47% values for the three sites, respectively. The new approach uses saturated layer’s resistivity values for porosity calculation, $\phi_{\rm{resistivity}}$. The resistivity values generated $F_{\rm{a}}$, $\rho_{\rm{w}}$ and $\rho_{\rm{o}}$ with constraints applied according to published reports for the parameters’ range of values. Conventional and normalized Waxman–Smits models were then employed for $\phi_{\rm{resistivity}}$. Conventional model produced $\phi_{\rm{resistivity}}$ of 12.66, 25.33 and 12.94%, while normalized model produced better $\phi_{\rm{resistivity}}$ values of 30.38, 31.91 and 27.32% for the three sites, respectively. Normalized model significantly outperforms with errors of <5%. Hence, the new approach accurately estimates saturated layer’s $\phi$ with no dependency on physical samplings and is applicable even in clay’s presence.

    • Tangential winds of a vortex system in a planetary surface layer

      SHEFALI UTTAM DEEPAK SINGH VARUN SHEEL

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      The planetary boundary layer (PBL) mediates interactions between the surface and free atmosphere. In Martian PBL, surface can force convective vortices leading to dust devils. We use the Navier–Stokes equations and the continuity equation to determine mean (with respect to time) tangential wind velocity in cylindrical co-ordinate system within the surface layer of a planetary atmosphere. We utilize Martian surface layer properties for theoretical derivation of our solution. However, our results remain valid for any planetary surface layer as long as all of our assumptions are valid. Our theoretical values of the tangential wind velocity lie well within the range of observed values. The derived equation represents the dependency of tangential velocity on both radial distances from the center of vortex, and the altitude. As we move further away from the vortex center, the effect of vortex becomes non-significant, and velocities start following the standard logarithmic profile. Due to dependency of tangential wind velocity on altitude, the tangential velocity increases as we move higher up in the vortex system. At 100 m altitude, for an order of magnitude increase in the radial distance, the mean tangential wind velocity drops by about a factor of 1.5 in magnitude.

    • Groundwater contamination in mega cities with finite sources

      AYAN CHATTERJEE MRITUNJAY KUMAR SINGH VIJAY P SINGH

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      Groundwater contamination due to multiple sources occurring in mega cities was modelled. One constant source contamination was considered at the source boundary, whereas other sources may join in between at various locations at different times. Initially, the aquifer was contamination-free in mega cities and was subsequently contaminated by means of different sources in due course of time. One-dimensional ADE (Advection Dispersion Equation) for modelling groundwater contamination was used and solved analytically in the semi-infinite aquifer domain for a finite number of point sources. A numerical solution wasalso obtained for two sources to compare analytical solutions. Results were examined for different velocity profiles to show the maximum contaminant concentration level with distance. This may be helpful to model the maximum possible number of point sources of contamination (i.e., it represents approximately what happens in the field situation). Some remedial measures may be taken to overcome these kinds of contamination problems in mega cities by treating the sources so that recharge of the aquifer is not affected.

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