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The article presents information about various papers related to geophysics. Some of the papers are "The Seismic Structure of the Saurashtra Crust in Northwest India and Its Relationship With the Reunion Plume," by G.S.P. Rao and H.C. Tewari, "Maximum Horizontal Stress Orientations in the Cooper Basin, Australia: Implications for Plate-Scale Tectonics and Local Stress Sources," by S. D. Reynolds, S. D. Mildren, R. R. Hulls, J. J. Meyer and T. Flottmann, "A Magnetic Field Model With Daily Variations of the Magnetospheric Field and Its Induced Counterpart in 2001," by V. Lesur, S. Macmillan and A. Thomson.

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]

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]

Concepts and approaches of earthquake risk reduction have evolved over time. The Great Kanto Earthquake of 1923 has paved the pathway of this long journey. 1995 the Great Hanshin-Awaji Earthquake has taught the importance of self help and mutual help in terms of community participation, volunteer activities, and role of civil society. In the first international decade of disaster risk reduction, two landmark earthquake risk reduction projects, namely risk assessment tools for diagnosis of urban areas against seismic disaster (RADIUS) and global earthquake safety initiative (GESI) have made significant impacts to scenraio-based risk assessment, and raising awareness of local governments mainly in developing countries to undertake decisive actions. The Kutch Earthquake of 2001 of India has prompted the need of owner driven reconstruction (ODR), which is considered inclusive as well as sustainable in long run. While the pre-disaster preventive measures for earthquake risks are challenging, the new complex global risk landscape poses additional challenges which need to be addressed to reposition earthquake risk reduction. It is argued that addressing systemic risks, active involvement of private sectors, role of new and emerging technologies, understanding priorities of new generation, and role of new entrepreneurship (in the form of Science-preneurship) are some of the future pathways to address the complexity of earthquake risk reduction. [ABSTRACT FROM AUTHOR]

Northeast India is one of the world's most seismically active regions. The event data included in this research for the period 1737–2012 is mostly obtained from worldwide database agencies such as ISC, NEIC, and GCMT. Historical seismicity is collected from published and unpublished documents and some earthquake events are collected from the Indian Meteorological Department Bulletins. As the Mw scale is developed and validated in the southern California region and overestimates the smaller magnitude earthquakes, therefore, recent literature suggested an improved version of the seismic moment magnitude scale (Mwg) applicable for the entire globe considering both long- and short-period frequency-spectra using modern instrumental data. To update the earthquake catalog of Northeast India, we prepared empirical relationships between different magnitudes to Mwg using robust statistical General Orthogonal Regression. A procedure is also suggested for converting different earthquake sizes towards seismic moment scale. The Magnitude of Completeness (Mc) and the Gutenberg–Richter (GR) recurrence parameter values for the declustered homogenized catalog in four time periods, namely 1737–1963, 1964–1990, 1964–2000, and 1964–2012, have been computed. Our analysis suggests that the use of the Mwg scale improves seismicity parameters 'b' up to 30%, 'a' up to 17%, and 'Mc' up to 18% for the Northeast India region. A complete unified earthquake catalog in terms of advanced seismic moment magnitude scale could help understand seismicity and earthquake engineering studies of the region. [ABSTRACT FROM AUTHOR]

The 2001 Gujarat earthquake was one of the most destructive intraplate earthquakes ever recorded. It had a moment magnitude of M w 7.6 and had a maximum felt intensity of X on the Modified Mercalli Intensity scale. No strong ground motion records are available for this earthquake, barring PGA values recorded on structural response recorders at thirteen sites. In this paper, synthetic ground motions are generated at surface level using the stochastic finite-fault method. Available PGA data from thirteen stations are used to validate the synthetic ground motions. The validated methodology is extended to various sites in Gujarat. Response spectra of synthetic ground motions are compared with the prescribed spectra based on the seismic zonation given in the Indian seismic code of practice. Ground motion characteristics such as peak ground acceleration, peak ground velocity, frequency content, significant duration, and energy content of the ground motions are analyzed. Response spectra of ground motions for towns situated in the highest zone, seismic zone 5, exceeded the prescribed spectral acceleration of 0.9 g for the maximum considered earthquake. The response spectra for towns in seismic zone 5 exhibit peaks in the low period ranges, indicating high vulnerability of low rise structures designed as per the provisions of the Indian seismic code of practice. The response spectra for towns situated in seismic zone 3 were considerably lower than the prescribed maximum spectral acceleration of 0.4 g. The substantial damage reported in towns situated in seismic zone 3 is due to poor construction practices and non-compliance with provisions of seismic design standards. [ABSTRACT FROM AUTHOR]

Fragility curves are useful tools for presenting the risk of structural damage from earthquakes as a function of a ground-motion parameter. Seismic hazard analysis for an area precedes the fragility analysis for structures built in that area. Many studies are available in the literature regarding probabilistic seismic hazard analysis (PSHA) and fragility estimation. However, a practical approach to integrate the hazard curve from PSHA and using the ground motion of that level to estimate fragility can be an area to explore further. In this study, an effort has been made to obtain peak ground acceleration (PGA) level at design-based earthquake (DBE) from PSHA. Based on this PGA value obtained, a fragility assessment has been performed. This study aims to obtain a fragility curve for a midrise RC frame building for DBE hazard level using PSHA. Three 6-story RC frame buildings are considered in this study for a seismically active zone in India. The buildings have been designed with the following performance objectives: (1) immediate occupancy (IO) with 1% drift, (2) life safety (LS) with 2% drift, and (3) collapse prevention (CP) with 3% drift. Incremental dynamic analysis (IDA) is performed using 22 numbers of far-field ground motions as prescribed by a strong ground-motion database to obtain the capacity of exceeding the respective drift limit states. Fragility curves for the three buildings are generated based on those capacities. The present study is a practical approach to capture the consequence of seismic hazard for an area and predicting the seismic risk. [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]

The economic development and rapid urbanization in hilly regions has accelerated the real estate development in India. Because of this, population density within the hilly region has increased enormously. Buildings situated in hilly region are configured differently consistent with the topographical condition. The bottom level for consecutive rows of column could also be different leading to buildings having step back and step back-setback configurations. The behaviour and response of such buildings is significantly different than buildings on plain ground because of combination of irregularity, mass irregularity and stiffness irregularity. Soft storey buildings have shown very poor performance in past earthquakes. G+5 Residential buildings with OGS on sloping ground under highly seismic areas are under study. The modelling of step back and step back-setback building with Infill brick masonry with and without Shear wall are to be provided at corners. The slope at which the structures are to be kept 15°, 25°, 35°and 45°. Different response parameters like the variation of Storey Displacement, Base shear, Storey drift, and Period of time with reference to variation in several sloping ground are studied with regard to fixed base. The analysis is performed by using equivalent static force method (ESFM), response spectrum method (RSM) and nonlinear time history method (NLTHM). For construction of the building on sloping ground the Step back-Set back building configuration is suitable, alongside shear wall placed the corner of the building. Corner shear wall provided good strengthening to the building on sloping ground. [ABSTRACT FROM AUTHOR]

The northeastern part of the Indian subcontinent, considered as the most active seismic zone of the Indian subcontinent, was hit by an earthquake of Mw 5.6 on January 3, 2017. The epicenter of this earthquake was Kanchanbari located in the Dhalai district of Tripura. The present study aims to assess the environmental and socio-economic impact of this earthquake in the vicinity of the epicenter. To assess and determine the level of damage, the affected areas were visited during the first week of the 2017 earthquake. Various Government offices were also consulted to acquire data on damages caused by the earthquake. Moreover, Remote Sensing and Geographical Information System (RS & GIS) techniques were applied to address the influence of this earthquake on bank erosion. During the field visit, the striking features of soil liquefaction generated by the earthquake were observed in the flood plain area of the Manu River. Landslide, with three casualties in India and the neighbor Bangladesh, and damages of infrastructure were also reported. Additionally, an assessment of the bank erosion study revealed that the rate of the post-earthquake bank erosion increased to 592%, compared to the pre-earthquake bank erosion within the study length of the Manu River. The findings highlighted that the impact of this earthquake is minimal. However, the seismotectonic features and observation of the liquefaction within the risk zone of the earthquake indicate a possible significant threat for the future. [ABSTRACT FROM AUTHOR]

The southern Kachchh Mainland (SKM) of western India, situated in a seismically active intraplate region with a considerable Quaternary landscape, provides an opportunity to reconstruct the roles of climate and tectonics. Employing geomorphology, detailed sedimentology supported by geochemistry and optical dating, we integrate the fluvial to fluvio‐marine records to evaluate the potential of dryland environments in archiving the palaeo‐events. The climate reconstructions suggest that the fluvial systems have responded to the variations in monsoonal strength through widespread aggradation during 57 until 41 ka, corresponding to the later part of the MIS‐3. Following this, a relative weakening of monsoon and onset of aridity is observed between 28 and 11 ka, with short spells of enhanced monsoon. The monsoonal conditions again strengthened during 11 to 6 ka, reaching its maximum during the Early Holocene optima, which triggered a sea‐level rise during the Middle Holocene period, that is, 6 to 3 ka. Following this, the sequences incised in response to the relative sea‐level fall to the present level in post 3 ka. We have also employed this OSL ages to reconstruct the phases of aggradation and incision of valley fill sediments/estuarine tidal terraces from the SKM during the last 57 ka. The present study illustrates and contributes to the advancement in understanding of complex processes and their influence on climatic/tectonic signals in dryland landscape as well as their decoupling. [ABSTRACT FROM AUTHOR]

Throughout the world, the tsunami generation potential of some large under-sea earthquakes significantly contributes to regional seismic hazard, which gives rise to significant risk in the near-shore provinces where human settlements are in sizeable population, often referred to as coastal seismic risk. In this context, we show from the pertinent GPS data that the transient stresses generated by the viscoelastic relaxation process taking place in the mantle is capable of rupturing major faults by stress transfer from the mantle through the lower crust including triggering additional rupture on the other major faults. We also infer that postseismic relaxation at relatively large depths can push some of the fault segments to reactivation causing failure sequences. As an illustration to these effects, we consider in detail the earthquake sequence comprising six events, starting from the main event of Mw =7.5, on 10 August 2009 and tapering off to a small earthquake of Mw =4.5 on 2 February 2011 over a period of eighteen months in the intensely seismic Andaman Islands between India and Myanmar. The persisting transient stresses, spatio-temporal seismic pattern, modeled Coulomb stress changes, and the southward migration of earthquake activity has increased the probability of moderate earthquakes recurring in the northern Andaman region, particularly closer to or somewhat south of Diglipur. [ABSTRACT FROM AUTHOR]

A new approach is developed to find the source azimuth of the ultra low frequency (ULF) electromagnetic (EM) signals believed to be emanating from well defined seismic zone. The method is test applied on magnetic data procured from the seismoactive region of Koyna-Warna, known for prolonged reservoir triggered seismicity. Extremely low-noise, high-sensitivity LEMI-30 search coil magnetometers were used to measure simultaneously the vector magnetic field in the frequency range 0.001-32 Hz at two stations, the one located within and another ∼100 km away from the seismic active zone. During the observation campaign extending from 15 March to 30 June 2006 two earthquakes (EQs) of magnitude (ML >4) occurred, which are searched for the presence of precursory EM signals. Comparison of polarization ellipses (PE) parameters formed by the magnetic field components at the measurement stations, in select frequency bands, allows discrimination of seismo-EM signals from the natural background ULF signals of magnetospheric/ionospheric origin. The magnetic field components corresponding to spectral bands dominated by seismo-EM fields define the PE plane which at any instant contains the source of the EM fields. Intersection lines of such defined PE planes for distant observation stations clutter in to the source region. Approximating the magnetic-dipole configuration for the source, the magnetic field components along the intersection lines suggest that azimuth of the EM source align in the NNW-SSE direction. This direction well coincides with the orientation of nodal plane of normal fault plane mechanism for the two largest EQs recorded during the campaign. More significantly the correspondence of this direction with the tectonic controlled trend in local seismicity, it has been surmised that high pressure fluid flow along the fault that facilitate EQs in the region may also be the source mechanism for EM fields by electrokinetic effect. [ABSTRACT FROM AUTHOR]