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The magnetotelluric (MT) investigation carried out in Koyna Seismogenic Zone (KSZ), an intra-plate earthquake region in Western India, along an E–W profile brings out moderately conductive (~ 700–1000 Ωm) near vertical features within the very high resistive (> 20,000 Ωm) granite/granite-gneiss basement. Occurrences of these anomalous moderate conductors are corroborated with sensitivity analysis. The alignment of earthquake hypocenters along the resistive–conductive boundary signifies the moderate conductor as basement fault. The conversion of resistivity values to the ratio of seismic P- to S-wave velocity (vp/vs) suggests that the moderate conductivity of the fault zone (as compared to the surrounding basement) appears due to the presence of fluid in the fault zone. Geophysical evidences reveal ~ 2.5–3.6 vol% fluid in the fault zone with ~ 1.8–2.6% interconnected porosity, which migrates along the structural boundary and invades the mechanically strong basement to nucleate the brittle failure within it. The present study proposes two mechanisms for the seismicity in the Koyna region. First: the meteoric water circulation due to the loading–unloading of nearby Koyna reservoir acts as potential fluid source for this triggered seismicity, which has also been suggested by previous studies. Second: the fluid circulation due to a deep-seated source. The present MT study brings out a conductive feature below 20 km depth which is thought to be emerged due to the dehydration of amphibole bearing rocks. The fluid generated from dehydration might act as a probable source to the triggered seismicity; since the conductive feature has a linkage to the upper crust. [ABSTRACT FROM AUTHOR]

This paper presents the ground motion amplification scenario along with fundamental frequency ( F) of sedimentary deposit for the seismic microzonation of Kolkata City, situated on the world's largest delta island with very soft soil deposit. A 4th order accurate SH-wave viscoelastic finite-difference algorithm is used for computation of response of 1D model for each borehole location. Different maps, such as for F, amplification at F, average spectral amplification (ASA) in the different frequency bandwidth of earthquake engineering interest are developed for a variety of end-users communities. The obtained ASA of the order of 3-6 at most of the borehole locations in a frequency range of 0.25-10.0 Hz reveals that Kolkata City may suffer severe damage even during a moderate earthquake. Further, unexpected severe damage to collapse of multi-storey buildings may occur in localities near Hoogly River and Salt Lake area due to double resonance effects during distant large earthquakes. [ABSTRACT FROM AUTHOR]

Recently developed region-specific GMPEs are used for a comprehensive seismic hazard analysis (SHA) of the North and Central Himalayas (NCH) using a probabilistic approach considering two source models. Vulnerable seismic sources in the areas are identified based on the Seismotectonic Atlas (Dasgupta et al. 2000), published by the Geological Survey of India. An up to date, homogenized and declustered earthquake catalogue is compiled from various sources, with earthquake data since 250 BC, to create a new digitized seismotectonic representation of the region. Regional seismic zones having similar seismicity are recognized based on the Gutenberg-Richter (GR) parameters and the region is delineated into 5 seismic zones. The study area is divided into grids of size 0.05° × 0.05° and the hazard in terms of Peak Ground Acceleration (PGA) at the centre of each grid point is estimated and presented as hazard maps for individual seismic sources, maximum of all sources, and average of both sources. From the current study, it could be concluded that the PGA estimated in the regions is comparatively higher than what is reported in the codal provisions for seismic zonation and estimation of design horizontal acceleration for the region. [ABSTRACT FROM AUTHOR]

Kurseong and its surrounding areas are frequently affected by the landslide which causes huge loss of properties and lives. The landslide susceptibility maps can play an important role in human development and sustainable environment management in Darjeeling Himalayan. The present research focused on preparing the effective landslide susceptible models using different statistical probabilistic methods, namely landslide nominal susceptibility factor (LNSF), information value (InfoVal) and certainty factor (CF) models. Experiments have been carried out in Kurseong region, a part of Darjeeling Himalaya as a field of this research. Landslide sites were identified from previous records through extensive field survey and Google pro satellite imagery. Totally, 273 landslide sites were compiled and prepared the inventory map. Out of 273 landslides, 70% were used for training and 30% were used for validating the models. Seventeen landslide conditioning factors were selected for modeling landslide susceptibility, i.e., elevation, aspect, slope degree, rainfall, geological structure, geomorphologic division, lineament, land use/land cover, distance to roads, earthquake zone, soil texture, soil depth, normalized difference vegetation index, drainage density, stream power index and topographic wetness index. The produced susceptibility maps were validated using the receiver's operating characteristic (ROC) curves. The prediction accuracy of LNSF, InfoVal and CF models as per ROC are 80.78%, 82.91% and 86.13%, respectively. The CF achieved the highest accuracy (86.13%), while the LNSF produced the lowest ROC value (80.78%). However, the comparison of the produced landslide maps revealed that all the applied models have good precision for studying susceptibility of landslide in Kurseong and its surrounding of Darjeeling Himalaya, India. The findings of current study can be supportive for the mitigation of landslide risk in the Kurseong range as well as the surrounding comparable areas having same geoenvironmental conditions. [ABSTRACT FROM AUTHOR]

Surface topography (whether subaerial or submarine) is a product of plate tectonic, geological, climate and surface processes. Plate tectonic processes, predominantly operated through earthquake cycle, dominate, at least in the seismically active regions, and are responsible for a significant amount of topography build up. On a shorter time scale, they appear to cause devastation, but on a longer time scale, they lead to the development of diverse landscapes which not only makes them look beautiful but also inhabitable. The topography build-up, due to deformation caused by earthquake processes, depends upon the mechanism of deformation and earthquake occurrence. The earthquake occurrence mechanism is different in the plate boundary regions as compared to that in the plate interior regions. Here in this article, I discuss the nuances of crustal deformation in the interplate and intraplate regions in the context of India and India plate. [ABSTRACT FROM AUTHOR]