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      Volume 129, All articles

      Continuous Article Publishing mode

    • 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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