Sankar K. Nath

Indian Institute of Technology Kharagpur | IIT KGP · Department of Geology & Geophysics

Indian subcontinent, marked by its intricate seismotectonic settings stands out as the most active region in the globe. This study conducts a firm rock-compliant Probabilistic Seismic Hazard Assessment considering both tectonic and polygonal sources in 0-25km, 25-70km, 70-180km, and 180-300km depth ranges, Next Generation Attenuation models through...

The Koyna-Warna seismic region located in western Indian state of Maharashtra, encompassing the south-western part of the Deccan Volcanic Province, reveals prolific seismicity attributed to both intraplate tectonism and reservoir-triggered activities. The 1967 Koyna earthquake of MW 6.3 marked the largest reported instance of Reservoir-Induced Seis...

The mountainous terrain of the East-Northeast tectonic ensemble covers an approximate area of 3,11,420 km2 comprising the Eastern Himalayan zone, Northeast India and Bhutan is prone to mass movements. The increasing trend of landslide occurrences in the last few decades sets loud alarm bells for mapping the landslide hotspot zones in terms of Lands...

Recent advancements in regional-scale slope displacement mapping have arisen from the urgent need for effective solutions to mitigate the consequences of seismically-induced landslides. The regions of Darjeeling, Kurseong, and Kalimpong have experienced significant slope failures due to a combination of seismic activity, intricate lithological comp...

The riverine country of Bangladesh, located on the world’s largest fluvio-deltaic sedimentary basin, called unified Bengal Basin, is exposed to extreme seismic threats due to proximity to seismogenic blocks of the Northeast India, East-Central Himalaya, and the basin itself, also impinging many strong earthquakes in the past with MM Intensity of VI...

The necessity for efficient solutions to minimize the damage caused by seismically induced landslides has prompted recent advances in methodologies for slope displacement mapping at the regional scale. However, the time horizon of hazardous occurrences is essential in rational hazard management. Kashmir Himalayas suffered tremendously from slope fa...

Punjab is a flat low land state occupied by thick deposits of various types of loose to dense soil due to active sedimentation and constitutes 1.53% of the geographical area of the country. The flat alluvial plains of Punjab have been formed by the deposition of Indo-Gangetic alluvium, with a maximum thickness of 300 meters over the base rocks of t...

Northeast India with complex geology and active tectonics has witnessed several devastating earthquakes viz. 1869 Cachar of MW 7.4, 1897 Shillong of MW 8.1, 1950 Assam of MW 8.7 with maximum MM intensity of VII-X, presenting a serious case for site-specific seismic hazard study. An updated Probabilistic Seismic Hazard at bedrock level with 10% prob...

Gangtok, the capital City of Sikkim suffered immensely from Slope failure problem due to complex geological setting, high intensity rainfall and seismic shaking. In the present study site-specific geophysical and geotechnical investigations have been carried out at Chandmari, a perennial sliding zone for slope stability analysis. In order to identi...

The Bengal Basin located in the eastern part of the Indian subcontinent at the conjunction of the Eurasian, Indian, and Indo-Burma plates with two progressing deformation fronts viz. the Himalayas and the Indo-Burmese orogenic belts is one of the largest fluvio-deltaic to shallow marine sedimentary basin covered by alluvial plains of Holocene depos...

The Bengal Basin located in the eastern part of the Indian subcontinent at the conjunction of the Eurasian, Indian and Indo-Burma plates with two progressing deformation fronts viz. the Himalaya and the Indo-Burmese orogenic belts is one of the largest fluvio-deltaic to shallow marine sedimentary basin covered by alluvial plains of Holocene deposit...

Northeast India with its complex topography, diverse geological and geomorphological setting, active tectonics and rapid urbanization is one of the deadliest earthquake prone county in the world being rocked from time immemorial by some devastating earthquakes like 1897 Shillong with Mw 8.1, 1934 Bihar-Nepal with Mw 8.1, 1950 Assam with Mw 8.7, 198...

The Bengal Basin of eastern Indian subcontinent, considered as the world’s largest fluvio-deltaic sedimentary basin, is located at the junction of three active tectonic plate boundaries viz. the Indian plate, the Eurasian plate and the Burmese plate, whose movements made the region exposed to constant seismicity. An attempt has been made here to un...

Landslide, mass movements and slope instability are common and serious geo-environmental problems in highland ecosystems, particularly in seismically active regions like the Himalayas. The Kashmir Himalaya suffered intensely from incidence of sporadic landslides due to complex geological setting, heavy rainfall and intense seismic shaking. In the p...

Soil liquefaction and associated ground failure are some amongst the major causes of infrastructure damage in unconsolidated, non-cohesive and water saturated alluvial terrains due to the impact of large earthquakes. Northeast India is the most seismically active region (Seismic zone V) of the country and experienced ground liquefaction by large ea...

Northeast India is the most seismically active region being located in Seismic Zone-V and experienced liquefaction phenomenon triggered by large earthquakes with maximum MM Intensity of X. The 1950 Assam earthquake of Mw 8.7, 1897 Shillong earthquake of Mw 8.1, 1869 Cachar earthquake of Mw 7.4 and 1988 India-Burma border earthquake of Mw 7.2 report...

Northeast India region presenting the most complex neotectonic assemblage is one of the world’s deadliest seismic territory being struck time and again by devastating earthquakes like the 1897 Shillong earthquake of Mw 8.1, 1934 Bihar-Nepal earthquake of Mw 8.1, 1950 Assam earthquake of Mw 8.7, and 1988 Burma-India border earthquake of Mw 7.2 being...

The Indian landmass comprising of three broad morphotectonic provinces, namely the Himalaya and Tertiary mobile belts, Indo-Gangetic Foredeep and Peninsular shield have been jolted time and again by catastrophic earthquakes. The Socio-economic Risk Map of India generated by integrating vulnerable exposures with the IBC-compliant surface-consistent...

A host of great historical earthquakes from the Himalayas and Northeast India reportedly triggered liquefaction with the surface manifestation of sand boil, ground subsidence and lateral spreading in West Bengal and its capital city Kolkata located in the alluvium-rich Ganga-Brahmaputra river system, thus presenting a strong case towards systematic...

The Eastern Boundary Zone of Northeast India, comprising the Indian States of Manipur, Mizoram and Nagaland, suffers immensely under the impact of frequent devastating landslides that results in widespread damage and casualty. A rough estimate of the decadal intensity of landslides from an inventory spanning over half a century calls for systematic...

Landslides and other mass movements are serious geo-environmental hazards in the Greater Gangtok region. It is intensified manifolded by human interferences in terrain. Massive landslides kill thousands of people with catastrophic damages in this region. Therefore, in the present study, a methodology for landslide susceptibility mapping has been de...

Landslide susceptibility (LSI) modeling of Darjeeling–Sikkim Himalaya is performed by integrating 28 causative factors on 28C28 combinations on Geographical Information System (GIS) following analytic hierarchy process (AHP)-based multicriteria decision protocol, logistic regression (LR)-based multivariate technique, machine learning data-driven ra...

Seismic risk map of the Indian subcontinent presented here places the tectonic ensemble of Westcentral Himalaya, Indo-Gangetic Foredeep, Bengal Basin, Darjeeling-Sikkim Himalaya to Northeast India including Bhutan in ‘High’ to ‘Severe’ Risk, thus rendering it a model case study for site-specific seismic hazard study based on an enriched surface and...

Landslide Susceptibility Zonation (LSZ) of Northwest Himalaya is performed by integrating twenty causative factors on Geographical Information System (GIS) in 1:50,000 scale by following a Machine Learning and Data Mining Algorithm-based Random Forest (RF) technique. Any Landslide Hazard modeling endeavor begins with putting in place a most authent...

Gangtok, the capital city of the Himalayan State of Sikkim, suffered immensely from the incidence of frequent devastating landslides inflicting damage to life and properties implicating severe socio-economic disruptions every year. An average decadal intensity of landslide spanning over half a century put an alarming growth in the region, necessita...

Landslide, mass movements and slope instability are common and severe geo-environmental problems in highland ecosystems, particularly in seismically active regions like Northeast India including Bhutan. In fact, wherever the mountain slopes are steep and fragile geological condition there is always a possibility of occurrence of disastrous landslid...

The Indo-Gangetic Foredeep region lies in close proximity to the Himalayan collision tectonics and the Peninsular Shield thereby subjecting it to repeated strong ground shaking from large and great earthquakes from these active tectonic regimes. An attempt is, therefore, made to understand the seismotectonic regime of the Indo-Gangetic Foredeep reg...

The common approaches for scattered interpolations are use of polynomial and piece-wise polynomial spline, geostatistical methods, and radial basis functions, etc. The interpolation schemes using kriging and radial basis functions have the advantage of being meshless and dimensional independent. However, for the data sets having insufficient observ...

The site response analysis of Kashmir valley during the 8 October 2005 Kashmir earthquake (Mw 7.6) using the standard penetration test ‘N value’ (SPT N) geotechnical dataset is presented. Due to non-availability of the strong motion data records, synthetic ground motions at the bedrock level were generated at each borehole location by the stochasti...

Liquefaction-induced ground failure is one amongst the leading causes of infrastructure damage due to the impact of large earthquakes in unconsolidated, non-cohesive, water saturated alluvial terrains. The city of Kolkata is located on the potentially liquefiable alluvial fan deposits of Ganga-Bramhaputra-Meghna Delta system with subsurface litho-s...

We present a stable meshless scheme for numerical solution of 2D Helmholtz equation using radial basis-finite difference (RBF-FD) method. The interpolants over a ‘user defined’ node arrangement are computed through a hybrid Gaussian-cubic kernel. Such a hybrid kernel reduces the ill- conditioning problem in the discretization, therefore, making it...

Pseudospectral (PS) methods are high order schemes for numerical solution of partial differential equations, in which the approximate solution is represented using a set of very smooth and global basis functions. In general, well-known polynomials serve as the basis functions in PS methods, which in higher dimensions, limit the algorithm to tensor-...

We present the seismic source zoning of the tectonically active Greater Kashmir territory of the Northwestern Himalaya and seismicity analysis (Gutenberg-Richter parameters) and maximum credible earthquake (mmax) estimation of each zone. The earthquake catalogue used in the analysis is an extensive one compiled from various sources which spans from...

Seismicity analysis is very much pertinent for Indian subcontinent and its adjoining region which is seismically active including many great earthquakes associated with collision and subduction tectonics in the northern, north-eastern part of the subcontinent and in the Andaman and Nicobar Island. An earthquake catalogue has been generated for Sout...

In the context of numerical approximation of partial differential equations, meshless methods are recent developments, which have been reported to be relatively straightforward, yet provide better convergence and accuracy as compared to the conventional mesh-based approaches, for some specific problems like stress–strain analysis and modeling in a...

An Extradosed Cable Stayed Bridge over River Hooghly in Hooghly and Nadia district of West Bengal, India will be constructed. The investigation site is located within close proximity of Eocene Hinge Zone. Considering the importance of the project, Site specific response spectra have been developed for the four zones to determine the zone factors. D...

this study presents the seismotectonics of the Hazara-Kashmir syntaxis and the surroundings. the detailed description of the origin, geology and structures of the Hazara-Kashmir syntaxis is presented. the structural alignment of the Hazara-Kashmir syntaxis is explained to be resulted by the shift in the motion pattern of the Indian plate from trans...

We present the liquefaction potential analysis of Kashmir valley alluvium in general with special emphasis to four benchmark localities. The synthetic ground motions from the site response analysis of the valley during the 8 October 2005 Kashmir earthquake of Mw 7.6 are used as input motions. To determine the dynamic properties of soil, 64 SPT (Sta...

http://www.j-igu.in/igu%2020-2%20(web)/Paper-1.pdf

Scattered data interpolation is a basic problem in many science and engineering disciplines where data is collected at irregularly spaced observation points and visualized at a finer scale including the points where there is no data. The common approaches for such interpolations are polynomial, piece-wise polynomial spline and radial basis function...

Chebyshev pseudospectral (PS) methods are reported to provide highly accurate solution using polynomial approximation. Use of polynomial basis functions in PS algorithms limits the formulation to univariate systems constraining it to tensor product grids for multi-dimensions. Recent studies have shown that replacing the polynomial by radial basis f...

We present the seismicity analysis of Chenab Valley Seismic Zone, the seismogenic source of Kirthai-I HEP. Chenab Valley is a tectonic pull-apart basin, situated to the southeast of Kashmir nappe and northwest of Chamba nappe in the northwestern Himalaya. Geologically, the Palaeozoic-Mesozoic sequences of the Kashmir and Chamba nappes are separated...

The Orr-Sommerfeld eigenvalue problem decides hydrodynamic stability in the analysis of parallel fluid flow in an idealized infinitely long domain. Spectral methods are reported to be a viable tools for numerical solution of an differential equation involving simple domain and smoothly defined problems. In this work, we present a spectral collocati...

The city of Kolkata is one of the most urbanized and densely populated regions in the world and a major industrial and commercial hub of the eastern and northeastern region of India. In order to classify the seismic risk zones of Kolkata we used seismic hazard exposures on the vulnerability components, namely land use/land cover, population density...

Seismic microzonation is a process of estimating site-specific effects due to an earthquake on urban centers for its disaster mitigation and management. The state of West Bengal, located in the western foreland of the Assam-Arakan Orogenic Belt, the Himalayan foothills and Surma Valley, has been struck by several devastating earthquakes in the past...

The Valley of Kashmir is a picturesque Neogene-Quartenary intermontane tectonic basin. Due to the active tectonic setup in and around the Kashmir valley, the Kashmir Himalaya in general and the valley in particular are vulnerable to the earthquake hazard. The earthquake hazard vulnerability of this region is evident from the historical accounts as...

The city of Kolkata is one of the most urbanized and densely populated regions in the world and a major industrial and commercial hub of the eastern and northeastern region of India. In order to classify the seismic risk zones of Kolkata we used seismic hazard exposures on the vulnerability components, namely land use/land cover, population density...

We appraise topographic-gradient approach for site classification that employs correlations between 30 m column averaged shear-wave velocity and topographic gradients. Assessments based on site classifications reported from cities across India indicate that the approach is reasonably viable at regional level. Additionally, we experiment three techn...

http://www.praiseworthyprize.org/jsm/index.php?journal=irehm&page=article&op=view&path%5B%5D=13451

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 broadb...

Online material : Data files for seismogenic source zones (polygons), smoothed-gridded seismicity models, and hazard curves at 0.2° regular grid spacing over the study region. Earthquake disasters occur mainly due to the collapse of buildings and structures triggered by ground motions. It is, therefore, important to predict ground-shaking levels i...

We compile a data set of 585 weak, broadband, and strong ground-motion recordings from 184 earthquakes covering hypocentral distances ranging from 9 to 436 km in northeast India and the northwest Himalayas. Source-normalized vertical-component Fourier amplitude S-wave spectra are used to study path-attenuation characteristics, namely, geometrical s...

The seismicity of a region is implicit of the causal faulting mechanisms and geodynamic diversity of the subsurface regime nucleating earthquakes of different magnitudes, several of which may be as devastating as ones historically reported in global perspective of tectonic complexity as in the case of India. Fractal analysis using box-counting meth...

Proper selection and ranking of Ground Motion Prediction Equations (GMPEs) is critical for successful logic-tree implementation in probabilistic seismic hazard analysis. The present study explores this issue in predicting peak ground accelerations at the rock sites in India. Macroseismic intensity data complemented with limited strong ground-motion...

India has about 25% of its geographical area in the mountainous terrain exposing it to wide spread landslides triggered by mainly earthquakes and rainfall. The methodology for Landslide Hazard Zonation (LHZ) and Risk Analysis in India has been carried out in the present study by integrating various thematic layers namely Engineering Geology, Geotec...

Kolkata, one of the oldest cities of India, is situated over the thick alluvium of the Bengal Basin, where it lies at the boundary of the zone III and zone IV of the seismic zonation map of India. An example of the study of site effects of the metropolitan Kolkata is presented based on theoretical modeling. Full synthetic strong motion waveforms ha...

Raghukanth (2010) compiled an earthquake catalog and performed statistical assessment of seismicity parameters for India, which consist of Gutenberg-Richter parameter b -value, activity rate λ5.0 for MW 5.0, and maximum earthquake m max. For the purpose, the author used overlapping circular spatial windows of radius 300 km; the center of each circl...

The 1897 Great Shillong earthquake revealed considerable seismic susceptibility in Guwahati City, such as soil liquefaction, landslides, and surface fissures. In an attempt to quantify the seismic vulnerability of the city based on geological, seismological, and geotechnical aspects concerning seismic site characterization, in-depth analysis was pe...

Surficial geological conditions are known to cause amplifications of earthquake ground motions, which are often manifested as associated damage patterns. Seismologists describe the level of earthquake damages in terms of seismic intensities, referred to as macroseismic data. Such data from historical earthquakes are useful in seismic hazard evaluat...

Different seismic hazard components pertaining to Bangalore city, namely soil overburden thickness, effective shear-wave velocity, factor of safety against liquefaction potential, peak ground acceleration at the seismic bedrock, site response in terms of amplification factor, and the predominant frequency, has been individually evaluated. The overb...

The probable mitigation and management issues of seismic hazard necessitate seismic microzonation for hazard and risk assessment at the local level. Such studies are preceded with those at a regional level. A comprehensive framework, therefore, encompasses several phases from information compilations and data recording to analyses and interpretatio...

In the last decade a number of large earthquakes have devastated the Asian continental region, including the 1998 MW 6.6 Afghanistan-Tajikistan, 1999 MW 7.6 Chi-Chi, 2001 MW 7.6 Gujarat, 2002 MW 6.1 Hindukush, 2004 MW 9.0 Sumatra-Andaman, 2005 MW 7.6 Kashmir, 2006 MW 6.3 Yogyakarta, and 2008 MW 7.9 Sichuan. Of these, the 1998 Afghanistan-Tajikistan...

The Talchir Basin, one of India's oldest basins, has been a subject of interest because of its rich coal deposits. The maximum thickness of the basin is about 1500 m. Beyond the basin is the hard metamorphic rocks of Precambrian age. The ambient noise survey data have been analyzed for the Talchir Basin using Nakamura's technique of horizontal–vert...

Guwahati is fast emerging as a multi-ethnic cosmopolitan city with a burgeoning population and rapid unplanned urbanization. It is a commercial hub, catering to eight states in northeast India. The city is located in the lower Brahmaputra Valley and underlain by thick alluvial deposits ranging from 25 to 600 m with granitic exposure at places. The...

Earthquake source parameters provide information about the source properties of individual shocks, which can serve as an important basis for generalization about, and synthesis of, strong ground motion. Source function is also one of the most important contributors to seismic hazard analysis because it provides information about the seismic energy...

Recent seismicity in the northeast India and its adjoining region exhibits different earthquake mechanisms – predominantly thrust faulting on the eastern boundary, normal faulting in the upper Himalaya, and strike slip in the remaining areas. A homogenized catalogue in moment magnitude, M W, covering a period from 1906 to 2006 is derived from Inter...

A comprehensive analytical as well as numerical treatment of seismological, geological, geomorphological and geotechnical concepts has been implemented through microzonation projects in the northeast Indian provinces of Sikkim Himalaya and Guwahati city, representing cases of contrasting geological backgrounds — a hilly terrain and a predominantly...

Teleseismic data recorded at the broadband seismological observatory of the Indian Institute of Technology (IIT) Kharagpur are analyzed to determine the seismic characteristics of the crust beneath the western Bengal basin. Receiver functions calculated from the teleseismic P waveform for a range of back azimuths show little variation in the Moho P...

In this paper, we present a seismic hazard scenario for the Garhwal region of the north-western Himalayan range, in terms of the horizontal Peak Ground Acceleration. The scenario earthquake of moment magnitude M w 8.5 has a 10% exceedance probability over the next 50 years. These estimates, the first for the region, were calculated through a stepw...

As devastating earthquakes continue to inflict widespread destruction to life and property and hinder the development of urban areas, the technical and scientific problems of seismic hazard assessment and risk-related issues warrant urgent attention. In this regard, seismologists play a key role in defining the source parameters of earthquakes and...

An earthquake hazard zonation map of Sikkim Himalaya is prepared using eight thematic layers namely Geology (GE), Soil Site Class (SO), Slope (SL), Landslide (LS), Rock Outcrop (RO), Frequency–Wavenumber (F–K) simulated Peak Ground Acceleration (PGA), Predominant Frequency (PF), and Site Response (SR) at predominant frequencies using Geographic Inf...

We attempt to estimate possible maximum earthquakes in the northeast Indian region for four seismic source zones, namely EHZ, MBZ, EBZ, and SHZ, which encapsulates the various seismogenic structures of the region and also for combined source zones taken as a single seismic source regime. The latter case exhibits a high maximum earthquake estimate o...

We examine the predominant natural hazards in West Bengal, along with an analysis of the prevalent disaster mitigation and management perspectives. Pre-hazard activities towards its mitigation are emphasized and explicated. In cognizance with the existence of multiple hazards in the region, a composite vulnerability map is prepared through integrat...

The Great Sumatra earthquake (26 December 2004, Mw 9.3) and the resulting tsunami have generated considerable interest amongst scientists and engineers to develop algorithms for phase detection in order to subsequently assess the seismic moment, radiated energy, source mechanism and rupture propagation to decide the possibility of developing an ear...

A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types at 6m 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), w...

The Darjeeling-Sikkim Himalaya lying between Nepal and Bhutan share the broad thrust geometries of the Himalayan belt, but differ from elsewhere along the arc in that the surface traces of the Main Central and the Main Boundary thrusts in the frontal part of the mountain belt are exposed within just a few kilometers of each other and the intervenin...

Teleseismic data recorded at the broadband seismological observatory of the Indian Institute of Technology Kharagpur (22.32deg N, 87.31deg E) were analysed to determine the seismic characteristics of the crust beneath the Bengal Basin. Receiver functions calculated from the teleseismic P-waveform for a range of backazimuths show little variation in...

Seismic microzonation and hazard mapping was undertaken in the Sikkim Himalaya with local site conditions and strong ground motion attributes incorporated into a geographic information system. A strong motion network in Sikkim consisting of 9 digital accelerographs recorded more than 100 events during 1998–2002, of which 72 events are selected with...

Strong motion recordings by the Sikkim Strong Motion Array (SSMA) of 80 events with good signal-to-background noise ratio (≥ 3) for magnitude between 3 to 5.6, have enabled estimation of source model and site response, and also the simulation of spectral acceleration for moderate-to-large earthquakes with 6 ≤ MW ≤ 8.3. A combined simulated and reco...

In this paper, we present a seismic hazard map of the Indian Himalayan State of Sikkim, lying between Nepal and Bhutan Himalaya, in terms of horizontal peak ground accelerations with 10% exceedance probability over the next 50 years. These figures, the first for the region, were calculated through a stepwise process based on (1) an estimation of th...

Global Seismic Hazard Assessment Program (GSHAP) has classified the Indian peninsula into several seismogenic zones. Considering the seismotectonic setting of the Sikkim Himalaya, sources 2, 3, 4, 5, 25, 26, 27 and 86 may be critical in contributing to the seismic hazard of the region. These seismogenic zones have been classified as Himalayan sourc...

The seismic ground motion hazard is mapped in the Sikkim Himalaya with local and regional site conditions incorporated through geographic information system. A strong motion network in Sikkim comprising of 9 digital accelerographs recorded more than 100 events during 1998–2002, of which 41 events are selected with signal-to-noise ratio 3 for the es...