• Volume 128, Issue 3

April 2019

• Occurrence of diamond in peninsular India and its relationship with deep Earth seismic properties

An improved shear wave velocity (V$_s$) structure of the lithosphere of peninsular India using the surface wave tomography from the ambient noise and earthquake waveforms suggests its bipolar character. While most of the geological domains of India are characterised by a uniform lithospheric mantle of V$_{s}$ $\sim$ 4.5 km/s, the three cratonic regions, eastern Dharwar, Bastar and Singhbhum, hosting most of the diamondiferous kimberlite fields, show significantly high V$_{s}$ of 4.7 km/s and above in their lower lithosphere beyond $\sim$ 90 km depth. The higher velocity could best be explained by the presence of diamond and/or eclogite along with peridotite in mantle. This unique relationship suggests the regional seismic image of lithosphere as a guide for exploration of diamonds.

• Groundwater faecal pollution observation in parts of Indo-Ganges–Brahmaputra river basin from in-situ measurements and satellite-based observations

More than quarter of underprivileged global population, who lack access to basic sanitation and clean drinking water, live in India. Consequently, every year, millions suffer with enteric diseases from drinking faecal-contaminated groundwater. The UN Sustainable Development Goal lists access to safe water and basic sanitation for all by 2030, as their sixth goal. For the first time, the role of economic improvement on decrease in water-borne faecal pathogens was studied across Indo-Ganges–Brahmaputra river basin (IGB) for almost last three decades, to delineate the long-term improvement trends of groundwater quality across India, as a consequence of development. Long-term temporal (1990–2017) and high-resolution spatial (administrative block scale, n$=$2217) datasets of water-borne faecal pathogen concentration in groundwater and satellite-based nightlight (NL) were used to investigate the statistical trends and causal relationships. Linear and nonlinear (Hodrick–Prescott) trend analyses, panel data analyses, Bayesian vector autoregression (VAR) and lead–lag causality (LLC) analyses were performed on aforesaid culled datasets. However, the efficiency of development in alleviating the water quality and public health, and relationship with economic development, has not been well understood. Here, for the first time, using long-term, high-spatial resolution (n$=$2217), annual in-situ measurements and multivariate statistical models, we show that the spatially variable groundwater faecal pathogen concentration (FC, 2002–2017, $-$1.39 $\pm$ 0.01%/yr) has been significantly decreased across the basin. In most areas, increasing satellite-based NL plays a significant role (NL, 1992–2013, 3.05 $\pm$ 0.01%/yr) in reduction of FC. However, in areas with low literacy rate surpass development. Enhanced decrease of faecal coliform concentration in groundwater possibly signifies the implementation of Clean India Mission since 2014.

• Estimation and spatial mapping of seismicity parameters in western Himalaya, central Himalaya and Indo-Gangetic plain

The present study attempts to assess the seismic hazard parameters (a, b and $M_{c}$) and their spatial variation in western Himalaya, central Himalaya and Indo-Gangetic plain areas (19–38$^{\circ }$N and 72–91$^{\circ }$E). The earthquake catalogue is prepared from different available sources, within a region of 500 km surrounding the study area, in moment magnitude scale. The maximum likelihood estimation method is used for spatial variation of seismicity parameters. The study area is disaggregated into small grids of 0.5$^{\circ }$ $\times$ 0.5$^{\circ }$, and the spatial variation of seismicity parameters is analysed for the complete catalogue period. A significant variation in seismicity parameters is observed while moving from west to east along the Himalayan belt within the study area. Due to significant variations in seismicity parameters, instead of assigning a lumped value of seismic hazard parameter to the entire region, distributed seismic hazard parameter is assigned by dividing the entire area into five zones, of similar level of seismicity. The estimated seismicity parameter a for these zones varies from 4.28 to 6.18, and for b, it varies from 0.80 to 1.03. Using these Gutenberg–Richter parameters a and b, the present study estimated the return periods and probability of different magnitudes of earthquake for each zone.

• An integrated study on the coseismic and post-seismic deformation of the 2010 Yushu earthquake based on InSAR analysis

We carry out an integrated study on coseismic and post-seismic deformation caused by 2010 Yushu earthquake sequence, including both mainshock and aftershocks, by using multi-scene ENVISAT/ASAR data on two adjacent tracks. We map the extended deformation region to the west of mainshock and show the westward extension of seismogenic fault of mainshock. Based on our whole deformation field derived from mosaic interferograms, the total length of seismogenic fault reaches ${\sim }$103 km longer than ${\sim}$71 km suggested by the previous report. Several coseismic interferograms with different time baselines have similar deformation patterns, which indicate that the influence of aftershocks and post-seismic slip on coseismic deformation field is limited. Also, we observe a clear and separate deformation area, ${\sim}$38 km to the west of the mainshock epicentre, with maximum displacement of ${\sim }$9 cm. The localised deformation is composed of two patches with opposite motion directions, where an aftershock cluster with at least 47 events (> Ms 3.0) occurred. We infer that this localised deformation is caused by aftershocks ruptured on a blind active fault. While a weak post-seismic deformation band along main rupture zone near mainshock epicentre is likely attributable to short-term afterslip.

• Recent geodetic mass balance and extent changes of very small glaciers in the Hulugou Basin, Central Qilian Mountains, China

Very small glaciers (< 0.5 km$^{2}$) account for more than 70% of the total number of glaciers in the Qilian Mountains. Despite their total area and volume being small, they are important water resources in the Hexi Corridor. While glacier monitoring mostly focuses on medium-sized and large valley glaciers (e.g., Qiyi Glacier and Laohugou Glacier No. 12) in the Qilian Mountains, little is known about very small glacier mass balance in this region. This study presents a geodetic mass balance of six very small glaciers in the Hulugou Basin by comparing Shuttle Radar Topography Mission (SRTM) C-band (2000) and airborne laser scanning (2012) digital elevation models (DEMs). The total glaciers’ area decreased by 23.6% at a rate of 0.024 km$^{2}$ a$^{-1}$ and the geodetic mass balance was $-$0.68 $\pm$ 0.11 m water equivalent (m w.e.) a$^{-1}$ from 2000 to 2012. Shiyi Glacier, as the monitored glacier in the Basin, had lost 10.9% of the surface area at a rate of 0.005 km$^{2}$ a$^{-1}$ and the geodetic mass balance was $-$0.53 $\pm$ 0.11 m w.e. a$^{-1}$ for the period. Climatic variations over the last decade showed a pronounced increase in summer temperatures. The warmer conditions probably explain the glaciers mass loss observed in the Hulugou Basin.

• Fold interference patterns in Meso-Proterozoic Champaner fold belt (CFB) Gujarat, western India

This paper documents three phases of folding within the Meso-Proterozoic Champaner Fold Belt (CFB) located at the eastern part of Gujarat, western India. The first phase (F$_{1}$) displays WNW plunging F$_{1}$ fold of moderately inclined nature in the schists of the Khandia Formation. The second phase (F$_{2}$) refolded F$_{1}$ along a similar trend to produce folds of tight isoclinal nature in the Khandia and Narukot quartzites. Additionally, these F$_{1}$ folds depict second-order tight, and F$_{2}$ folds as first-order open type in the younger sequences of the CFB with varying amplitude vs. wavelength ratio. The ratio for F$_{1}$ folds ranges from 2:1 to 3:1, obtained along 3–4 m length across 3–6 m$^{2}$ area, whereas for F$_{2}$ folds the ratio ranges from 1:4 to 1:5 and is obtained along 1–2.5 km length across 0.5–1.5 km$^{2}$ area. The fold interference pattern developed on account of F$_{1}$ and F$_{2 }$ folds has resulted into Type-III or hook-shaped geometry regionally. The last phase of folding is characterised by N–S trending F$_{3}$ folds of open type over kilometre long limbs of F$_{1}$ and F$_{2}$ folds. The superposition of F$_{1-3}$ folds developed map scale Type-I or Dome and Basin geometry over Type-III superposed folds. The overall compressional direction for F$_{1}$ and F$_{2}$ folds ranges from N–S to NNE–SSW and for F$_{3}$ ranges from E–W to ESE–WNW.

• Hydrogeochemical modelling to understand the surface water–groundwater interaction around a proposed uranium mining site

The interaction between surface water and groundwater is a complex process and is considered as an important component for controlling the mining activities. The objective of this study is to understand the interaction between surface water and groundwater around a proposed uranium mining site by geochemical modelling. Surface water and groundwater samples along the groundwater flow path were collected from September 2013 to June 2016 across the uranium mineralised region located near Gogi, Karnataka, India. Collected water samples were analysed for major ion and uranium concentrations. This hydrochemical data was used as input in the geochemical modelling code PHREEQC to calculate the uranium speciation and saturation indices. Inverse geochemical modelling was performed along the flow direction by considering the mineralogical composition of host rock. Measurement of surface water and groundwater level indicates that the recharge and discharge of this region were primarily controlled by rainfall. Relation between the temporal variation of rainfall and saturation index of mineral reveals the various scenarios of interaction between surface water and groundwater around the mineralised region. Silicate/carbonate weathering, irrigation return flow and dissolution of evaporites are the major processes indicated by inverse geochemical modelling, which controls the hydrogeochemical evolution of water in this region. Geochemical modelling was effectively used to understand the temporal changes in the interaction between surface water and the groundwater in a uranium mineralised region.

• Organic geochemical characteristics of Jurassic petroleum system in Abadan Plain and north Dezful zones of the Zagros basin, southwest Iran

Jurassic succession has resulted in prolific oil and gas reservoirs in southwest Iran. In order to geochemically investigate the Jurassic petroleum system and assess the source rock of these hydrocarbons, 32 source rock samples (from well cutting and surface section) and 4 condensate samples were analysed using geochemical approaches. Rock-Eval pyrolysis and vitrinite reflectance measurement were done on rock samples. Then, condensate samples and source rock extracts were subjected to gas chromatography, gas chromatography–mass spectrometry and isotopic analyses in order to establish oil–oil and oil–source rock correlation. The hydrocarbon generation prediction was then confirmed by petroleum system modelling. The results indicated that the middle Jurassic Sargelu Formation with average total organic carbon (TOC) and hydrogen index values of 3.8% and 600 mg HC/g TOC, respectively, can be classified as good to excellent source rock with kerogen of type II. The maturity indicators revealed late oil to wet gas generation window for the Jurassic Sargelu Formation. Biomarker parameters showed marine carbonate source rock with advanced level of thermal maturity for the source rock of the condensates. Furthermore, there were good correlations between Jurassic Sargelu Formation and the studied oil and condensate samples which proved the Sargelu Formation as the main source rock of the Jurassic petroleum system in the study area. The basin modelling results also confirmed late oil to wet gas window maturity for the Sargelu Formation enabling it as a source rock for generating gas condensate accumulation in southwest Iran. The hydrocarbon generation from Sargelu Formation began in the late Cretaceous and its peak expulsion occurred in the Miocene time.

• Roundness of survivor clasts as a discriminator for melting and crushing origin of fault rocks: A reappraisal

Roundness of survivor clasts (mineral/rock fragments) in fault rocks (e.g., pseudotachylyte and cataclasite/gouge) has been used by some workers to distinguish melt-origin from crush-origin of such rocks. Keeping in view the large overlap in the published data on the roundness of fault rocks, the reliability of such a discriminator appears somewhat uncertain. The present study attempts to reappraise the aforesaid criterion through roundness analysis of quartz and feldspar clasts in melting-dominated pseudotachylyte (M-Pt), crushing-dominated pseudotachylyte (C-Pt) and fault-related cataclasite (F-Ct) collected from Sarwar–Junia Fault Zone in Rajasthan and from Gavilgarh–Tan Shear Zone in central India. Our analysis shows that roundness of clasts cannot reliably distinguish between fault rocks of melt-origin and crush-origin (especially M-Pt and F-Ct) as the roundness values overlap and a distinct limit of roundness value for each rock type cannot be established. While the roundness of clasts in M-Pt and C-Pt may be enhanced due to melt-induced rounding off of the initially angular clasts, rounding of clasts can also occur by abrasion during rolling of crushed material in F-Ct. Furthermore, anomalous thermal expansion of clasts in melt-origin pseudotachylyte may cause disintegration of larger clasts into smaller angular fragments, thereby increasing the percentage of angular clasts in melt-origin fault rocks. Therefore, roundness of survivor clasts cannot be solely used as a discriminator between melt-origin and crush-origin fault rocks.

• Evidence for active faulting in the eastern part of the Gulf of Saros, northern Aegean, from high-resolution seismic data

This study focuses on the determination of the near-surface tectonic features in the eastern part of the Gulf of Saros, a highly active seismic region within the North Anatolian Fault Zone. Approximately 350-km-line high-resolution seismic data were acquired to understand the active tectonic setting of the inner side of the gulf. The Ganos Fault, which generated the 9 August 1912 earthquake (Mw = 7.3) in western Turkey, enters into the Gulf of Saros from the east, cuts the southern margin of the gulf forming a trough which becomes broader and deeper westward. The seismic data reveal that the fault is not made up of a single segment or a pair of border faults bounding the trough. According to the seismic images of the fault segments, however, the emanating earthquake energy will possibly be carried by two different faults; namely the Ganos and Saros segments. These fault segments will be presented first in this paper in detail from new collected seismic data at the inner part of the gulf, and will be used to help a new tectonic model that explains how the Ganos segment controls the northern margin of the trough while the Saros segment controls the central part of the main trough. The latter is responsible from the development of an active basin and it forms the sudden deepening observed on the trough.

• Possible seismo-ionospheric precursor of the 12 February 2014 Yutian earthquake in China

On 12 February 2014, a major earthquake occurred near the Yutian County, China. In this paper, the ionospheric variations around the time of this earthquake were analysed on the basis of the global positioning system vertical total electron contents (VTEC) and computerised ionospheric tomography (CIT) electron density distributions. Three ionospheric anomalies on 2, 17 and 19 February were detected with the global VTEC data from Center for Orbit Determination in Europe before and after the earthquake. Based on the analysis of the geomagnetic indices, we think the anomalies on 17 and 19 February could be related to the geomagnetic disturbances. Through further investigations on the temporal and spatial characteristics of the anomaly on 2 February, we draw the conclusion that the pre-earthquake ionospheric anomaly is probably the seismo-ionospheric precursor of the Yutian earthquake. In addition, the CIT results of the anomaly on 2 February were used to study the vertical distribution of this anomaly. The results showed that the ionospheric anomaly was mainly concentrated at the heights between 200 and 400 km.

• Stratigraphical and morphological aspects of the northern Marmara shelf based on seismic data

Recent sedimentation and Plio-Quaternary stratigraphy of northern Marmara shelf has been investigated by high-resolution seismic datasets. Seismic data indicate that a thin cover of Plio-Quaternary unit (termed Unit 1) overlies the Miocene/Oligocene age older sediments (termed Unit 2). The erosional surface between Unit 1 and Unit 2 is the regional unconformity for the shelf formed during the last sea level low stand. Unit 1 is subdivided into two sub-units as Unit 1a for Holocene deposits accumulated after the last glacial maximum (LGM) and Unit 1b for fluvial sediments deposited during the last low stand of the Marmara Sea. The thickness of the Holocene sediments is maximum at SW of Bosphorus outlet, in the Buyukcekmece Bay and along the coastal area between Silivri and Buyukcekmece reaching approximately 32 m. Mean sedimentation rate of the entire northern shelf is calculated as 0.4 m/1000 yr for the last 12,000 yr based on the Holocene sediment thickness. There are four depressions in the western part of the shelf, which correspond to palaeolakes during the LGM filled by Plio-Quaternary sediments. Transition from lacustrine to marine conditions in the palaeolakes occurred when the Marmara Sea level exceeded −62 m threshold depth during the sea level rise following the LGM at approximately 12,500–13,000 yr before present (BP).

• Long-term (2005–2012) measurements of near-surface air pollutants at an urban location in the Indo-Gangetic Basin

Simultaneous long-term measurements of near-surface air pollutants at an urban station, New Delhi, were studied during 2005–2012 to understand their distribution on different temporal scales. The annual mean mass concentrations of nitrogen dioxide (NO$_{2}$), sulphur dioxide (SO$_{2}$), particulate matter less than 10 $\mu$m (PM$_{10}$) and suspended particulate matter (SPM) were found to be 62.0 $\pm$ 27.6, 12.5 $\pm$ 8.2, 253.7 $\pm$ 134 and 529.2 $\pm$ 213.1 $\mu$g m$^{3}$, respectively. The 24-hr mean mass concentrations of NO$_{2}$, PM$_{10}$ and SPM were exceeded on $\sim$ 27%, 87% and 99% days that of total available measurement days to their respective National Ambient Air Quality Standard (NAAQS) level. However, it never exceeded for SO$_{2}$, which could be attributed to reduction of sulphur in diesel, use of cleaner fuels such as compressed natural gas, LPG, etc. The mean mass concentrations of measured air pollutants were found to be the highest during the winter/post-monsoon seasons, which are of concern for both climate and human health. The annual mean mass concentrations of NO$_{2}$, PM$_{10}$ and SPM showed an increasing trend while SO$_{2}$ appears to be decreasing since 2008. Air mass cluster analysis showed that north–northwest trajectories accounted for the highest mass concentrations of air pollutants (more prominent in the winter/post-monsoon season); however, the lowest were associated with the southeast trajectory cluster.

• Carbon sequestration and CO$_{2}$ absorption by agroforestry systems: An assessment for Central Plateau and Hill region of India

India ranks fourth in terms of greenhouse gas (GHG) emissions and accounts for 6% of total GHG emissions in the world. Carbon dioxide (CO$_{2}$) has major contribution of 76% in total GHG emissions. Agroforestry that integrates trees in the agricultural landscape is regarded as a strategy for both adaptation and mitigation of climate change. Agroforestry plays an important role in reducing the level of GHG emissions vis-a-vis atmospheric CO$_{2}$ through carbon sequestration. Carbon sequestration is the process involved in carbon capture and the long period storage of atmospheric CO$_{2}$. In the present study, firstly area under agroforestry was estimated in Central Plateau and Hill region (agro-climatic zone-8) using satellite remote sensing data. Secondly, dynamic CO$_{2}$FIX model v3.1 was used to assess the baseline total carbon and carbon sequestration potential (CSP) of agroforestry systems for a simulation period of 30 yr. Finally, equivalent CO$_{2}$ absorption was assessed with the help of estimated agroforestry area and net CSP in the zone. Estimated area in Central Plateau and Hill region is about 1.96 million ha, which is 5.18% of total geographical area of this zone. Total carbon sequestered at zone level was estimated to be 17.81 Tg (tera gram) C and equivalent CO$_{2}$ absorption is at 65.36 Tg. The CSP of agroforestry systems would be about 158.55 Tg C for a simulated period of 30 yr or CSP would be 5.28 Tg C yr$^{-1}$ at country level. On the other hand, equivalent CO$_{2}$ absorption was 586.50 Tg for a period of 30 yr or would be 19.55 Tg yr$^{-1}$ at country level. Hence, the present study concludes that agroforestry has significant contribution in reduction of atmospheric CO$_{2}$ which would have much more if the area under agroforestry and/or number of trees ha$^{-1}$ on farmlands are increased.

• Statistical analysis of urban regional pre-monsoon rainfall in and around Kolkata, India

The present study aims at statistical analysis of pre-monsoon rainfall at Kolkata, India over a span of 45 yr (1970–2014) with special emphasis on the effect of urbanisation on pre-monsoon rainfall at Alipore, a core area of Kolkata (22$^{\circ}$34$^{\prime}$N; 88$^{\circ}$24$^{\prime}$E) India, where the urbanisation is almost static during the period 1970–2014 and Dumdum (22$^{\circ}$65$^{\prime}$N; 88$^{\circ}$45$^{\prime}$E), the outer periphery of Kolkata, where the urbanisation is still an ongoing process. As pre-monsoon rainfall is an effect of mesoscale convective development (horizontal dimensions 5–500 km), the two stations namely Dumdum and Alipore which are nearly 22 km apart from each other are taken into consideration in this study. To determine the possible changes in the pre-monsoon rainfall in both stations, a non-parametric Wilcoxon Signed Rank Sum test is conducted. This test reveals that the annual average pre-monsoon rainfall increased at Dumdum in post-urbanisation period, i.e., 1991–2014 compared to Alipore during the same period. It is important to note that the result of statistical analysis almost tallies with that of the geographical one.

• Gridded data as a source of missing data replacement in station records

The quality of available station data over western Himalayan region (WHR) of India is poor due to missing values, and hence quantifying climate change information at the station level is more challenging. The present study investigated the extent to which the available two different resolutions gridded rainfall data from the India Meteorological Department (IMD) namely, IMD-0.25$^{\circ}$$\times 0.25^{\circ} (IMD.25) and IMD-1^{\circ}$$\times$1$^{\circ}$ (IMD1) and global observational gridded data from the Climate Research Unit (CRU-0.5$^{\circ}$$\times$ 0.5$^{\circ}$) of UK can be used as a substitute to replace the missing values in IMD station data. Long-term time series produced at each station location showed that IMD.25 data was much closer to observation both in magnitude and patterns compared to CRU and IMD1. The seasonal and annual scale performance of these gridded data has been evaluated through different agreement and error indices. The agreement indices showed higher values in case of IMD.25 data while IMD1 and CRU indicated poor results. Similarly, the estimated errors are minimum in IMD.25 and maximum in CRU data. Finally, an overall agreement index (OAI) was developed by the combined influence of all the agreement indices. The results of OAI for each station revealed that in more than 77% of cases, the performance of IMD.25 gridded data to reproduce station level rainfall is superior as compared to IMD1 (<63%) and CRU (<46%) data. Therefore, it is concluded that the IMD.25 gridded data may be reliably used as a substitute data source in place of missing rain-gauge data over the WHR.

• Spatial analysis of landslide susceptibility using failure rate approach in the Hindu Kush region, Pakistan

This paper analyses and applies a spatio-statistical failure rate (SSFR) technique for landslide susceptibility zonation in the Hindu Kush region, Pakistan. The study area (Shahpur valley) is located in the eastern Hindu Kush mountain system. In Shahpur valley, land sliding is a recurrent and costly extreme event. Geologically, this region constitutes the youngest mountain systems and almost every year landslide-induced losses are reported. The frequency and intensity of landslide events is expected to further increase in future due to rapid population growth over the fragile slopes, infrastructural development and deforestation. In order to achieve objectives of the study, data were obtained from both primary and secondary sources. In Shahpur valley, an inventory of the past 300 landslide events of various sizes has been identified and marked on a SPOT satellite image of 2.5 m resolution. In order to identify the influence of landslide triggering factors, such as geology, tectonic structures, land use, slope angle, slope aspect, roads and streams, a univariate SSFR technique has been tested and applied for calculating the susceptibility score in each class of the selected parameters. Based on factor maps and cumulative score, the landslide susceptibility zones have been developed and validated appearing to be significantly reflecting the pattern of the past landslide events.

• Impact of different types of meteorological data inputs on predicted hydrological and erosive responses to projected land use changes

Hydrological responses to land use/land cover (LULC) changes are complex in nature and tend to have an impact on the hydrological cycle, affecting the livelihood of the inhabitants. Rainfall–runoff models, such as the Soil and Water Assessment Tool, were used in the past to unravel the interactions between the impacts of climate and land use changes. However, the sensitivity of the model outcome, regarding the hydrological and erosive response to climatic data derived with different methods, has not been fully understood. We carried out a hydrological simulation using (a) Climate Forecast System Reanalysis data set, which synthesises outputs of global climate models along with gauged weather information and has a global coverage, and (b) purely weather station-based gridded climate data provided by Indian Meteorological Department. A possible LULC scenario for the year 2020 was created using the combined Cellular Automata–Markov model. Application of both climate data sets resulted in a modest increase in the predicted streamflow and sediment yield as a response to the probable development scenario in 2020. However, the marked variations emerged in the location and monthly pattern of significant changes in the surface runoff and sediment yield in response to the likely LULC scenario for 2020 vis-a-vis 2010.

• Observed trends in indices for daily rainfall extremes specific to the agriculture sector in Lower Vellar River sub-basin, India

Globally, climate change has caused changes in frequency and intensity of climate extremes such as heat waves, droughts, floods and tropical cyclones. There is a need to understand the pattern of regional climate extremes to develop crucial adaptation strategies for the farming community. This paper focuses on developing the Expert Team on Climate Risk and Sector-specific Indices for rainfall, relevant for the agriculture and food security sector. The indices have been developed for Lower Vellar River sub-basin, a coastal basin in Tamil Nadu, India. Trend analysis has been done for the climatic and cropping seasons in the sub-basin. Overall, there has not been any trend in the annual rainfall index values. The monthly trend values for the different indices have mostly exhibited insignificant trends throughout the study period (1978–2015) except for a few indices. Overall, the southwest monsoon season has shown a significantly decreasing trend in the indices. The northeast monsoon season has shown insignificant trends with positive slopes for most indices. There were insignificant or no trends in the indices for the summer season. The findings from the study can be used as a guiding tool for developing adaptation strategies, for the farming community.

• C-equivalent correction factor for soil organic carbon inventory by wet oxidation, dry combustion and loss on ignition methods in Himalayan region

Soil organic carbon (SOC) is an important parameter to study the carbon cycle as soil carbon stock inventory as well as to serve as prime indicator in assessing soil health and soil quality. The present study was attempted to investigate C-equivalent correction factor for SOC by Walkley–Black (wet oxidation) and loss on ignition (LOI) methods in relation to TOC analyzer (dry combustion) method. TOC analyzer method supposed to be the best method of total soil organic carbon estimation. Soil sample from 77 sites representing dominant land use/land cover types of crop land, forest and scrub cover were collected in Himalayan region of Uttarakhand state, India. Surface (0–15 cm) and sub-surface (15–30 cm) soil samples were used for estimation of SOC by these three methods. C-equivalent correction factor ranged from 1.10 to 1.17 for SOC determination by Walkley and Black method to TOC analyzer method, whereas it varied from 0.257 to 0.417 for soil organic matter (SOM) by LOI method to TOC analyzer for soils under various land use/land cover types in the Himalayan region. The recovery of SOC by Walkley–Black method varied from 86.84 to 91.04% in the soils of various land use/land cover in the Himalayan landscape. Thus, there is need to develop specific correction factor for soils under various land use/land cover types for improved estimation of soil carbon stock. The regression models developed in the study can be directly used to obtain TOC analyzer equivalent total carbon contents in the soils (surface and sub-surface) for computation of soil carbon stock in Himalayan region.

• Peshtasar basalts: An example of post-collision basalts in sedimentary basin of Moghan, NW Iran

With an east–west exposure trend, Peshtasar Complex, which is located in the sedimentary basin of Moghan, northwestern Iran, is lithologically varied. The main constituent minerals are plagioclase, clinopyroxene and iddingsitised olivine in basalts and plagioclase megacryst, clinopyroxene and leucite in tephrite. The studied rocks are plotted in the fields of basaltic trachy-andesite, trachy-andesite and tephri-phonolite in the total alkali-silica (TAS) diagram as well as high-K to calc-alkaline and shoshonite fields. The chondrite normalised pattern of rare earth elements indicates the enrichment of LILE and LREE as well as the depletion of HFSE and HREE. Nb and Ti have a negative anomaly in the spider diagram. Eu/Eu* represents a positive anomaly for Eu indicating the frequency of calcic plagioclase and low oxygen fugacity in rocks. Geochemical parameters and diagrams predict a magmatic evolution via assimilation – fractional crystallisation process. According to the Ce/Yb vs. Ce diagram, partial melting has happened within the garnet–lherzolite field in the depth of ${\sim}$100 km. Based on $^{87}$Sr/$^{86}$Sr, Shahyourdi samples have EM1 sources, whereas Germi and Tazehkand basalts have EM11 sources that are indicative of different mantle sources for basalts in the western Moghan of the central and eastern areas. Basalts are found in active continental margins associated with the post-collision arcs.

• Variability in the ice sheet elevations over Antarctica derived from repetitive SARAL/AltiKa radar altimeter data (2013–2016)

Changes in surface elevations of polar ice sheets are the result of changes in ice dynamics and surface mass balance. Here, we present intra- and inter-annual elevation changes over the Antarctic ice sheet using the AltiKa radar altimeter’s 40 Hz geophysical data record products for the period 2013–2016. Slope corrections were applied on the elevations using a digital elevation model (DEM) available from NASA’s ice, cloud and land elevation satellite (ICESat). Comparison of elevations from AltiKa and ICESat’s DEM yielded correlation, bias and root-mean-square-deviation values of the order of 0.99, −2.88 and 23.04 m, respectively, indicating the first-level accuracy of a former dataset. Further comparison of Airborne Topographic Mapper dataset with AltiKa derived elevation yielded 0.4 m root-mean-square-deviation over a part of Vostok subglacial lake. The intra-annual change indicates that for GY2 (glaciological year), GY3 and GY4, number of negative elevation change points exceeded the number of positive elevation change points during the Antarctic austral summer period (December–February). Inter-annual elevation changes were negative during 2013–2014 and positive during 2014–2015 over east Antarctica, whereas in west Antarctica negative elevation changes were observed for both periods.

• Shallow subsurface imaging of the Wagad active fault system (Kachchh, northwestern India) by time domain electromagnetic studies

The Kachchh rift basin (KRB) in the northwestern Indian shield is one of the most seismically active intraplate regions of the world. It has witnessed four large earthquakes in the past two centuries that leads the region most vulnerable for seismic hazard. For effective seismic hazard assessment, detailed information on faults and its subsurface geometry is essential. Recently, shallow subsurface geophysical studies, particularly electrical resistivity studies have become a successful practice in imaging of fault zones and their attribute. In the present study, we carried out the time domain electromagnetic (TDEM) investigations across the Wagad highland of eastern KRB to map shallow subsurface structure and imaging fault zones in terms of resistivity. Resistivity section obtained after combining one dimensional models of 21 sites display significant details of the fault structures and geometry of shallow basin infill down to 200 m. The shallow layer of the basin infill across the South Wagad fault (SWF) and the North Wagad fault has a wedge shape made of unconsolidated deposits with thickness of $\sim$15–20 m. We infer that it might be due to syntectonic sedimentation due to the footwall subsidence across a branch fault of the SWF. The section indicates a $\sim$60–65 and 50–55 m estimates of cumulative throws for the SWF and NWF, respectively. Across the Gedi fault, the section indicates least block displacements, which might either be due to dominate strike-slip nature of faulting or more activeness of NWF compared to GF during the recent geological past. The results from the study affirm the ongoing Holocene deformation in the region signifying active nature of these faults.

• Estimating shear wave velocity of soil using standard penetration test (SPT) blow counts in Mashhad city

This study investigates the correlation between shear wave velocity (V$_{S}$) and standard penetration test blow counts (SPT-N value) in all soil types, gravelly soil, sandy soil and clayey soil for Mashhad city in the north eastern region of Iran. The V$_{S}$ data used were measured through downhole method in 84 construction projects (in 88 boreholes). From among collected data, 424 pairs of V$_{S}$-SPT recorded in one depth were used for regression analysis. The obtained results showed that the N-value had a critical role in estimating V$_{S}$ and soil type was less effective in this regard. These findings are in line with the findings of the previous studies. Regression equations obtained in this study were compared with correlations from previous studies. There was a relative similarity between the previously published and the new regression equations for Iranian soils. Although almost all correlations follow a similar trend, there are significant differences between new equations and correlations reported for other countries. The regression coefficients of the new equations show the acceptable capability of the suggested correlations in estimating V$_{S}$ through SPT-N value. Therefore, these equations can be used to estimate V$_{S}$ for the soils of the current study area and for other similar areas. Moreover, V$_{S30}$ was used for site classification of the study area as per National Earthquake Hazard Reduction Program (NEHRP) guidelines and it was shown that a major portion of the city comes under site class C and other locations are categorised as site class D.

• An exposition into the changing climate of Bengal Duars through the analysis of more than 100 years’ trend and climatic oscillations

Duars is located along the foothills of the Eastern Himalayas with an assemblage of forest cover. It extends from the river Tista in West Bengal to the river Dhunseri in Assam. Within this broad outline, the areal extension between the rivers Tista and Sankosh covering West Bengal is now known as the Bengal Duars or Western Duars and the rest of the portion that lies in the Assam district is named as the Assam Duars or Eastern Duars. In the present study, multi-decadal variability and trends of climatic events (temperature and extreme rainfall) in the Bengal Duars region have been analysed based on long-term dataset (more than 100 years). This region has experienced an increasing trend of temperature. The results show that the average temperature increases by 0.027$^{\circ}$C year$^{-1}$ and extreme rainfall becomes 5% higher than earlier since 1975.

• Monazite and xenotime U–Th–Pb$_{\rm{total}}$ ages from basement rocks of the (central) Shillong–Meghalaya Gneissic Complex, Northeast India

Monazite and xenotime are the two most useful and commonly used geochronometers for deciphering ages from metamorphic rocks. The low analytical cost involved in electron probe micro-analyser chemical dating, ease of sample preparation and abundance in metamorphic rocks of wide P–T conditions make monazite and xenotime dating most widely used technique for age determination amongst metamorphic petrologists. This contribution presents age comparisons between coexisting monazite and xenotime in the basement metapelitic rocks of the central part of the Shillong–Meghalaya Gneissic Complex (SMGC). Thermobarometric estimates in the studied samples indicate granulite facies conditions of metamorphism with peak P-T conditions of $\sim$6.5 kbar and ${\sim}$750$^{\circ}$C. Results indicate that xenotime in the basement rocks in the central SMGC formed in four discrete geological events while monazite either formed only in the latest Pan-African granulite grade metamorphic event or recrystallised during this event. Monazite in the studied samples yielded a single ubiquitous age of ca. 500 Ma. Xenotime in the study area, although found in only one sample, preserves four distinct ages at 1153 $\pm$ 29, 930 $\pm$ 36, 823 $\pm$ 41 and 490 $\pm$ 11 Ma. Preservation of Grenvillian ages in xenotime from central SMGC marks the eastward extension of Rodinia amalgamation front in the Indian Shield. The Neoproterozoic ages in xenotime from central SMGC suggest that the ca. 820 Ma high-grade metamorphism in the Eastern Indian Tectonic Zone had a wider impact in the SMGC than perceived previously.

• L-band scintillation and TEC variations on St. Patrick’s Day storm of 17 March 2015 over Indian longitudes using GPS and GLONASS observations

The aim of the present study is to investigate the response of ionospheric total electron content (TEC), Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) scintillations during 17 March 2015 St. Patrick’s Day geomagnetic storm over Visakhapatnam, which is popularly known as Waltair (WALT) in the literature. GPS TEC observations obtained from five IGS stations (SGOC, IISC, HYDE, LCK4 and LHAZ) and WALT during the storm have been compared. The TEC derived from GPS, GLONASS constellations and CODE global ionosphere TEC map (GIM) over WALT has also been compared. Positive storm effect during the main phase of the storm and negative storm effect during the recovery phase of the storm were observed over the said stations. The variation of northern equatorial ionisation anomaly TEC (CODE GIM TEC maps) in response to the St. Patrick’s Day storm over four Indian longitudes (75$^{\circ}$E, 80$^{\circ}$E, 85$^{\circ}$E and 90$^{\circ}$E) has also been presented. Strong amplitude and phase scintillations were observed in the L-band signals of GPS and GLONASS constellations over WALT. Twelve satellite (Pseudo Random Noise) PRNs of GPS L1 and nine PRNs of each GLONASS L1 and L2-band signals were affected by strong amplitude and phase scintillation. The peak amplitude scintillation index (S4) obtained from the effected PRNs of GPS L1 signal and GLONASS L1-band signals over WALT range from 0.36 to 0.74 and 0.36 to 0.76, respectively. Strong fluctuations in rate of TEC index are noted over the said stations. This enhanced scintillation activity is mainly due to the main phase of the storm falls in the evening sector over the Indian region.

• Modulation of active-break spell of Indian summer monsoon by Madden Julian Oscillation

The Madden Julian Oscillation (MJO) is the major fluctuation in tropical weather on weekly to monthly time scale and a major driver of Indian summer monsoon (ISM). In this study, using Indian Meteorological Department (IMD) high resolution daily gridded rainfall data and Wheeler-Hendon MJO indices, the daily rainfall distribution over India associated with various phases of eastward propagating MJO was examined to understand the MJO–monsoon rainfall relationship. The present study reveal that the onset of break and active events over India and the duration of these events are strongly related to the phase and strength of the MJO. The break events were relatively better associated with the strong MJO phases than the active events. About 80% of the break events were found to be set in during the phases 1, 2, 7 and 8 of MJO with maximum during phase 1 (34%). On the other hand, about 58% of the active events were set in during the MJO phases 3–6 with maximum during phase 6 (21%). The results of this study indicate an opportunity for using the real time information and skillful prediction of MJO phases for the extended range prediction of break and active conditions.

• Magma mixing in Neoarchean granite from Nalgonda region, Eastern Dharwar Craton, India: Morphological, mineralogical and geochemical evidences

We present field, petrographic, mineralogical and whole-rock geochemical data for part of the Neoarchean granite and associated microgranular enclaves (MEs) occur in the Nalgonda region, NE part of Eastern Dharwar Craton (EDC), and demonstrate the end-member magma mixing processes in the petrogenesis of the host granite. Extensive occurrence of ME and uni-directional flow band structures (N–S trend) in all the studied outcrops exposed over about 20 km depict that intensive magma mixing–mingling occurred at magma chamber scale. MEs are the portions of intermediate mafic magma that had interacted at two stages with acidic host granite. Mixing at the initial stage promoted efficient thorough mixing which resulted in rapakivi texture and mesocratic enclaves. Wispy filament structures around these enclaves indicate that mafic magma globules were mechanically diluted in the host granite magma by chaotic advection. These filamental magmas were further linearly diluted along with convection-related flow of the host magma. Smaller mafic globules also got linearly stretched along with this flow. Upon solidification of the host magma, these wispy mafic filaments were preserved as flow structures. The second stage of mafic magma mixing did not promote thorough mixing due to the large viscosity contrast with the host granite magma and preserved their physical entity. These enclaves are melanocratic with sharp boundary and devoid of gradational contact and filament structures around it. They characteristically show network of granitic vein injection which often show crenulation folding. These evidences indicate that during the second-stage interaction, the enclave magma was rigid to plastic nature with respect to the host granite magma. Coherent linear Harker variation trend of CaO, MgO, TiO$_{2}$, K$_{2}$O/Na$_{2}$O, V, Y and Sc indicates that mixing has promoted to develop chemical gradient between ME and host granite magmas. Mechanical dilution by chaotic advection must have enhanced the chemical diffusion of both magmas. Smooth decreasing Harker trend of Y content in both the magmas indicates that they had undergone certain degree of fractional crystallisation. In contrast, elements like Rb, Ba and Sr with large value of diffusion coefficient (D) show scattered behaviour in element–element plots suggesting that diffusive fractionation was active during chaotic advection mixing. It is concluded that heterogeneity in compositional variation of Nalgonda granite can be attributed to difference in degree of mechanical dilution of mafic magma, fractional crystallisation and diffusive fractionation. The geochemical evidences indicate the role of subduction in the evolution of these rocks.

• An attribute recognition model to predict the groundwater potential of sandstone aquifers in coal mines

The groundwater potential prediction of sandstone aquifers is an important pre-requisite for the implementation of reasonable and effective measures to prevent mine water inrush disasters. In this study, an attribute recognition model was combined with entropy weighting to predict the groundwater potential of sandstone aquifers in coal mines. Five evaluation indices were selected to predict groundwater potential, such as sandstone thickness, sandstone lithology coefficient, flushing fluid consumption, fracture fractal dimension and fold fractal dimension. On the basis of data analysis, the groundwater potential was classified into four levels. Confidence and improved score criteria were applied to attribute recognition. The main advantages of this model are that it enables both the prediction and quantification of the groundwater potential of sandstone aquifers. The model’s results were compared with those from a comprehensive geographic information system evaluation. The final model results were in good agreement with the observed results, proving that this attribute recognition model is accurate and effective for groundwater potential prediction.

• Evaluation and prediction of meteorological drought conditions using time-series and genetic programming models

Over the years, a number of prediction methods have been proposed for the evaluation of probability of hydrological–meteorological variables or drought indices. In this study, the precipitation data recorded in four stations of northwestern Iran over the period 1960–2014 were used to develop the time-series and genetic programming (GP) models. Comparison of the observed and predicted data showed that although both models have acceptable accuracy in predicting precipitation, the time-series models had lower errors than the GP models. So, the autoregressive and periodic autoregressive moving average models were chosen as the superior models for annual and monthly series, respectively. Therefore, the Standard Precipitation Index (SPI) and Z-Score Index (ZSI) were used to assess the drought conditions. According to the results, the SPI recognised a higher percentage of historical and prediction periods as drought conditions than ZSI. The validation of indices showed that the ZSI was more capable for detecting the drought and wetness conditions. The trend analysis of SPI and ZSI showed significant decreasing trends in different stations at all-time scales, except yearly in Urmia and all-time scales in Zanjan, which statically had no significant trend. In conclusion, given the current precipitation trends, the droughts are increasing in both severity and numbers.

• Geochemistry and mineral composition of lamprophyre dikes, central Iran: implications for petrogenesis and mantle evolution

Late Proterozoic–Early Cambrian magmatic rocks that range in composition from mafic to felsic have intruded into the Hour region of the central Iranian micro-continent. The Hour lamprophyres are alkaline, being characterized by low contents of SiO$_{2}$ and high TiO$_{2}$, Mg# values, high contents of compatible elements, and are enriched in LREE and LILE but depleted in HFSE. Mineral chemistry studies reveal that the lamprophyres formed within a temperature range of ${\sim}$1200$^{\circ}$ to 1300$^{\circ}$C and relatively moderate pressure in subvolcanic levels. The Hour lamprophyres have experienced weak fractional crystallization and insignificant crustal contamination with more primitive mantle signatures. They were derived from low degree partial melting (1–5%) of the enriched mantle characterized by phlogopite/amphibole bearing lherzolite in the spinel-garnet transition zone at 75–85 km depth, and with an addition of the asthenospheric mantle materials. We infer the Hour lamprophyres to be part of the alkaline rock spectrum of the Tabas block and their emplacement, together with that of other alkaline complexes in the central Iran, was strongly controlled by pre-existing crustal weakness followed by the asthenosphere-lithospheric mantle interaction during the Early Cambrian.

• On the estimation of hydraulic conductivity of layered vadose zones with limited data availability

Vadose zone acts as a controlling agent for recharge and transport of contaminants into aquifers. Hence, for modelling and quantifying flow and transport processes in subsurface environments, hydraulic conductivity (K) of the vadose zone plays an important role. However, given the heterogeneity and anisotropy of subsurface systems, the in-situ measurement of K is a daunting task at a larger scale. The present study was conceived to evaluate the efficacy of salient pedotransfer functions (PTFs) to indirectly estimate the saturated hydraulic conductivity ($K_{\rm{s}}$) of a lateritic vadose zone of eastern India. Also, in-situ hydraulic conductivity along with basic soil physical properties was determined in different vadose-zone layers at three locations (bare plot, cultivated field and orchard). Four PTFs [Campbell, Rawls–Brakensiek/Cronican–Gribb (R–B/C–G), and Models 2 and 3 of Rosetta] were selected to estimate $K_{\rm{s}}$ and their performances were evaluated. Based on the statistical indicators, it is concluded that Model 3 of Rosetta is capable of predicting relatively close values of $K_{\rm{s}}$ for the lateritic vadose zones to some extent. To generalise the findings of this study, it is recommended that such field-based studies should be carried out at a larger scale in lateritic terrains with varying land use/land cover.

• # Journal of Earth System Science

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Volume 128 | Issue 8
December 2019

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