Prioritization of soil conservation measures using erodibility indices as criteria in Sikkim (India)

Erodibility indices are important parameter that can be used to describe the intensity of the soil erosion problems causing environmental concerns. These indices are convenient to estimate the susceptibility to erosion where physical measurement is very difficult. Sikkim is one such state in India where measuring erosion is a tedious process due to its difficult and inaccessible terrain conditions. In the present study, spatial variation of susceptibility of erosion in East district of Sikkim was estimated by using indices such as clay ratio, dispersion ratio, mod clay ratio and critical level of soil organic matter. The result indicates soils in East district are mostly dominated by sand particles (40.5–81.06%) in majority of soil samples. The dispersion ratio values in most of the soils were >15% indicating very high vulnerability to erosion. The values of clay ratio (3.44–9), modified clay ratio (mean value of 6.9) and critical level of soil organic matter content (<5%) indicated high susceptibility to erosion. The trends of indices were generated by IDW interpolation method to understand the spatial variation of the susceptibility to erosion. The interpolated maps were overlaid on subwatershed maps to prioritize the subwatershed for planning treatment measures.     

Cross-Association Analysis of Barren Measures Lithologies and Microfacies,Talcher Coalfield,Odisha

Cross-association analysis of lithologies and microfacies of two borehole sections of the Barren Measures Formation, Talcher coalfield situated 12 km apart show strikingly dissimilar results. In case of lithologies, one-to-one correlation becomes significant, which suggests continuity of the formation throughout the Barren Measures Formation and prevalence of braided stream depositional environment. However, lack of significant correlation of microfacies suggests existence of different sub-environments at different parts of the Barren Measures Formation during each stage of sedimentation. When channel facies were laid down at one place, homotaxial leeve, floodplain and swamp facies were deposited elsewhere.     

Tectonic and lithologic control over landslide activity within the Larji–Kullu Tectonic Window in the Higher Himalayas of India

The purpose of this study is to analyze and characterize recent landslide events in the Larji–Kullu Tectonic Window (LKTW), and to establish a relationship between the tectonic and lithologic characters of the terrain and the landslides activity. Using multispectral satellite image analysis with selected field investigation, a landslide occurrence database has been generated for the period between 1984 and 2015. To decipher the accelerated occurrences of landslides in the region, an integrated study is undertaken in the Kullu (also known as Kulu) valley of Beas River basin within the LKTW complex, to analyze the litho-structural and terrain slope interactions using morpho-tectonic parameters such as Topographic/Bedding Plane Interaction Angle (TOBIA) index, terrain surface roughness index and lithological competency analysis. A prominent clustering of landslides is observed in the north of Sainj River, contained within the tectonic window. Major sites of landslides are found to be located in the intensely fractured Manikaran Quartzite occurring within the core of the LKTW. The landslides are mostly associated with southern and southwestern-facing slopes and activations are pronounced in the ‘Orthoclinal’ slope class with gradient of 37°–48°. Thematic maps, e.g., geological, structural, geomorphological, slope and slope-aspect maps are generated and considered together to understand the morpho-tectonic scenario of the tectonic window. Observations from the above-stated thematic maps along with the occurrences of moderate magnitude earthquake epicenters helped to infer neotectonic movements along the Sainj River fault. Tectonic upliftment of the northern bank of the Sainj River along with increased precipitation through decades has resulted in recurrent landslides within the LKTW.     

First Order Seismic Microzonation of Delhi,India Using Geographic Information System (GIS)

A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types at 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform. The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP), wherein each thematic map is assigned weight in the 5-1 scale: depending on its contribution towards the seismic hazard. Following the AHP, the weightage assigned to each theme are: PGA (0.333), soil (0.266), geology (0.20), groundwater (0.133) and bedrock depth (0.066). The thematic vector layers are overlaid and integrated using GIS. On the microzonation theme, the Delhi region has been classified into four broad zones of vulnerability to the seismic hazard. They are very high (> 52%), high (38–52%), moderate (23–38%) and less ( < 23%) zones of seismic hazard. The “very high” seismic hazard zone is observed where the maximum PGA varies from 140 to 210 gal for a finite source model of M_w 8.5 in the central seismic gap. A site amplification study from local and regional earthquakes for Delhi region using Delhi Telemetry Network data shows a steeper site response gradient in the eastern side of the Yamuna fluvial deposits at 1.5 Hz. The ‘high’ seismic hazard zone occupies most of the study area where the PGA value ranges from 90 to 140 gal. The ‘moderate’ seismic hazard zone occurs on either side of the Delhi ridge with PGA value varying from 60 to 90 gal. The ‘less’ seismic hazard zone occurs in small patches distributed along the study area with the PGA value less than 60 gal. Site response studies, PGA distribution and destruction pattern of the Chamoli earthquake greatly corroborate the seismic hazard zones estimated through microzonation on GIS platform and also establishes the methodology incorporated in this study.     

Probabilistic Assessment of Earthquake Recurrence in Northeast India and Adjoining Regions

Northeast India and adjoining regions (20°–32° N and 87°–100° E) are highly vulnerable to earthquake hazard in the Indian sub-continent, which fall under seismic zones V, IV and III in the seismic zoning map of India with magnitudes M exceeding 8, 7 and 6, respectively. It has experienced two devastating earthquakes, namely, the Shillong Plateau earthquake of June 12, 1897 (M _w 8.1) and the Assam earthquake of August 15, 1950 (M _w 8.5) that caused huge loss of lives and property in the Indian sub-continent. In the present study, the probabilities of the occurrences of earthquakes with magnitude M ≥ 7.0 during a specified interval of time has been estimated on the basis of three probabilistic models, namely, Weibull, Gamma and Lognormal, with the help of the earthquake catalogue spanning the period 1846 to 1995. The method of maximum likelihood has been used to estimate the earthquake hazard parameters. The logarithmic probability of likelihood function (ln L) is estimated and used to compare the suitability of models and it was found that the Gamma model fits best with the actual data. The sample mean interval of occurrence of such earthquakes is estimated as 7.82 years in the northeast India region and the expected mean values for Weibull, Gamma and Lognormal distributions are estimated as 7.837, 7.820 and 8.269 years, respectively. The estimated cumulative probability for an earthquake M ≥ 7.0 reaches 0.8 after about 15–16 (2010–2011) years and 0.9 after about 18–20 (2013–2015) years from the occurrence of the last earthquake (1995) in the region. The estimated conditional probability also reaches 0.8 to 0.9 after about 13–17 (2008–2012) years in the considered region for an earthquake M ≥ 7.0 when the elapsed time is zero years. However, the conditional probability reaches 0.8 to 0.9 after about 9–13 (2018–2022) years for earthquake M ≥ 7.0 when the elapsed time is 14 years (i.e. 2009).     

Ground-motion predictions in Shillong region, northeast India

We deliver ground-motion prediction equations for Shillong region, northeast India, based on a database generated by finite-fault stochastic simulations. An examination of the regional seismic source characteristics is carried out beforehand. Micro/minor earthquakes (M _W?<?5.0) nucleating at hypocentral depth <21?km in the region recorded at broadband seismic stations are observed to have Brune stress-drop ranging between 2.8 and 99.9?bars. Likewise, macroseismic intensity data for the 1897 Shillong Earthquake that nucleated at a hypocentral depth of ~35?km places the associated stress-drop at 100?200?bars. The apparent variation of the stress-drop parameter with depth is considered with two source zones namely lower-crust and upper-crust. Equations for the lower-crust predict higher ground-motion levels and exhibit affinity to those developed for stable continental region of Eastern North America. The ground-motion levels predicted by the equations for the upper-crust are relatively lower but are still higher compared with those predicted for tectonically active regions, viz., the Himalayas and Western North America.     

Cyclic sedimentation of the Karharbari Formation (Damuda Group), Talchir Gondwana basin, Orissa

The cyclic arrangement of lithofacies of the Karharbari Formation of the Damuda Group from a part of the Talchir Gondwana basin has been examined by statistical techniques. The lithologies have been condensed into five facies states viz. coarse-, medium-, fine-grained sandstones, shale and coal for the convenience of statistical analyses. Markov chain analysis indicates the arrangement of Karharbari lithofacies in form of fining upward cycles. A complete cycle consists of conglomerate or coarse-grained sandstone at the base sequentially succeeded by medium-and fine-grained sandstones, shale and coal at the top. The entropy analysis categorizes the Karharbari cycles into the C-type cyclicity, which is essentially a random sequence of lithologic states. Regression analysis undertaken in the present study indicates the existence of sympathetic relationship between total thickness of strata (net subsidence) and number and average thickness of sedimentary cycle and antipathic relationship between number and average thickness of sedimentary cycle. These observations suggest that cyclic sedimentation of the Karharbari Formation was controlled by autocyclic process by means of lateral migration of streams activated by intrabasinal differential subsidence, which operated within the depositional basin and the channels carrying coarse grade clastic sediments, which make the cycles thicker, tend to be more common in the areas of maximum subsidence. Clastic sediments issued from the laterally migrating rivers interrupted the cyclic sedimentation of the Karharbari Formation in many instances.     

Mobility of arsenic in West Bengal aquifers conducting low and high groundwater arsenic. Part I: Comparative hydrochemical and hydrogeological characteristics

The present study demonstrates the importance of hydrogeochemical characteristics (groundwater flow and recharge) of an aquifer in the release of As to groundwater. The study area (∼20 km²) is located in Chakdaha block, Nadia district, West Bengal, which hosts groundwaters of variable As content. The spatial distribution pattern of As is patchy with areas containing groundwater that is high in As (>200 μg L⁻¹) found in close vicinity to low As (<50 μg L⁻¹) groundwaters (within 100 m). The concentration of groundwater As is found to decrease with depth. In addition, the data shows that there is no conspicuous relationship between high groundwater As concentration and high groundwater abstraction, although the central cone of depression has enlarged over 2 a and is extending towards the SE of the study area. The river Hooghly, which forms the NW boundary of the study site, shows dual behaviour (effluent and influent during pre- and post-monsoon periods, respectively), complicating the site hydrogeology. The observed groundwater flow lines tend to be deflected away from the high As portion of the aquifer, indicating that groundwater movement is very sluggish in the As-rich area. This leads to a high residence time for this groundwater package, prolonging sediment–water interaction, and hence facilitating groundwater As release.     

Geohydrological evaluation of upper agniar and vellar basins,tamil nadu: An integrated approach using remote sensing,geophysical and well inventory data

The present paper focuses mainly on the assessment of groundwater availability in the Upper Agniar and Vellar basins. The remote sensing data was used to map the geomorphological units and structural pattern. The integration of geomorphology and structural pattern with geophysical and well inventory data reveals that shallow groundwater occurrence is controlled by geomorphological characteristics whereas at intermediate depth faults/fractures control the yield of groundwater. The study has also indicated that the eastern part of the basins is more favourable for groundwater development than the western part.