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The stability of buildings in seismic prone areas depends upon the structural behavior of buildings subjected to ground motion. Buildings of plan and vertical irregularities with respect to either geometry or stiffness have exhibited poor performance during past earthquakes . Identification of seismic building vulnerability is required for metropolitan cities which have moderate to high level of seismic proneness and have a high building density. Inspection of a large number of buildings individually requires enormous time and manpower. Using aerial photograph approach in GIS platform is an ideal choice to overcome these constraints. Chennai city is the thirty-fourth largest city in the world and prone to moderate earthquake hazards. This paper presents a methodology to analyze and predict the seismic vulnerability of buildings with five storeys and above in Chennai. Aerial photographic data of all buildings, land features and roads, within the city and its direct surroundings, were digitized and incorporated on a GIS platform, resulting in a digital vector map. A number of structural parameters determined on the basis of engineering knowledge and observations through rapid visual screening (RVS) have been used to identify the plan and vertical irregularities of the buildings. A new vulnerability scoring system to identify the level of damageability has been introduced based on RVS technique and compared with traditional grading system. Subsequent to RVS, a database of buildings having different range of vulnerability scores has been prepared. The percentage of desirable and undesirable features of buildings with respect to their contribution to damage was assessed based on past experiences and vulnerability scores of buildings. The survey shows that 30 % of the buildings are in the A category of being vulnerable to collapse. There are no buildings that can be classified as defect-free. It is also to note that 55-70 % of buildings lie in the category of D (low damage vulnerability). [ABSTRACT FROM AUTHOR]

The response of subsoil strata subjected to seismic excitations plays an important role in governing the response of the overlying superstructures at any site. Ground response analysis (GRA) helps to assess the influence of soil characteristics on the propagating seismic stress waves from the bedrock level to the ground surface during an earthquake. For the northeastern region of India, located in the highest seismic zone in the country, conducting an extensive GRA study is of prime importance. Conventionally, most of the GRA studies are carried out using the equivalent linear method, which, being a simplistic approach, cannot capture the nonlinear behavior of soil during seismic shaking. This paper presents the outcomes of a one-dimensional effective stress based nonlinear GRA conducted for Guwahati city (located in northeast India) incorporating the non-Masing load/unload/reload characteristics. The various ground response parameters evaluated from this study help in assessing the ground shaking, soil amplification, and site responses expected in this region. 2D contour maps, which are representative of the distribution of some of these parameters throughout Guwahati city, are also developed. The results presented herein can serve as guidelines for the design of foundations and superstructures in this region. [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]

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]

This study provides site characterization results using passive seismic techniques for the easternmost part of Shillong plateau of Northeastern India. The prime objective of this research is to generate the Horizontal-to-Vertical Spectral Ratios (HVSR) from earthquakes and ambient microtremor data for generation of 1-D shear wave velocity profiles to reveal the basement depths and fundamental resonance frequencies underneath three stations of Shillong plateau. The earthquake waveforms are recorded for a period of eighteen months (i.e. December 2018 to June 2020) using broadband seismometer; while the ambient microtremor data is collected from a three component highly sensitive velocity meter. The earthquake HVSRs and noise HVSRs are consistent with each other and range from ∼3.6 Hz to ∼14.5 Hz. The Rayleigh wave ellipticity are generated from the corresponding HVSR curves for inversion to determine compressional and shear wave velocity structure. We report that the compressional and shear wave velocity profiles match fairly well for both earthquakes and ambient microtremor data. Overall, Vs30 lies in the range of 480 m/s to 2600 m/s at all locations in the easternmost part of Shillong plateau; while the sedimentary layer velocity lies between 450 m/s and 1100 m/s. The thickness of the sedimentary layer is assessed from the velocity profiles and using an empirical formula makes a good match and varies from 11.3 m to 31.2 m. [ABSTRACT FROM AUTHOR]

The earthquakes have the most dominating societal and economic impact on the built environment. The earthquakes in an intraplate region are infrequent but often damaging. The uncontrolled urban growth in cities due to population explosion and migration makes it necessary to assess seismic hazards in an active region. It provides parameters for seismic safety and helps in disaster mitigation. The Kachchh Rift Basin (KRB) of western India is a seismically active intraplate region where many damaging earthquakes have occurred in the past (Mw 7.8 in 1819, Mw 7.6 in 2001). The KRB hosts many economic corridors and ports. Though the region has been put in a category with highest seismic hazard, the entire region is not prone to high hazards. The primary objective of the study is to integrate major attributes that influence seismic hazard on a GIS platform and prepare a multi-criteria-based hazard map by multi-criteria decision process named as analytical hierarchy process (AHP) developed by Saaty. In this study, the information about some of the attributes like peak ground acceleration (PGA), geology and geomorphology, and tsunami hazard is taken from published literature, whereas shear wave velocity to 30 m depth (Vs)30 and amplification factor were obtained through empirical relationships. The integration of these different attributes was performed, and weights were assigned depending on their contribution to the seismic hazard. The multi-criteria approach reveals that the southwestern part comprising of Kachchh mainland has a low hazard as compared to central and northern parts and almost 1 million people and around 0.18 million houses are exposed to moderate to high hazard. Large swaths of land are prone to liquefaction hazard. The corridor comprising of Bhuj, Bhachau and Rapar needs seismic microzonation. This macro level hazard map will be beneficial for the urban planners and government authorities to decide the areas, where seismic microzonation or site-specific studies are required that would help in mitigating earthquake disasters in the future. [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]

Northeast India is seismically most active region in India, and it falls under Zone V which represents the highest seismic risk in the country. This region has been experienced two great earthquakes like the 1897 Shillong (Mw 8.1) and the 1950 Assam earthquake (Mw 8.4) and several large earthquake (Mw ≥ 7) during last 122 years. Probabilistic approach and number statistical tools have been used by various researchers for finding the future earthquake recurrence rates. Using the earthquake catalogue, Gutenberg–Richter parameter has been estimated to evaluate seismic risk for six different regions: Eastern Himalayan, Indo-Burma region, Bengal Basin, Shillong Plateau, Mishmi Thrust, and Naga Thrust. Assuming that the earthquake occurrence is Poisson model, based on the obtained Gutenberg–Richter (G–R) relations, the probability of occurrence of earthquake of specified magnitude in given time is estimated for six seismotectonic regions. Further in this study, we made an attempt to estimate the probability of earthquake using four known statistical models, namely Exponential, Rayleigh, Weibull, and Pareto. The whole region is divided into six tectonic blocks to estimate the probability of an earthquake (Mw ≥ 5.5) through the maximization of conditional probability of earthquake occurrence. Time intervals for the occurrence of the next large earthquake in the six regions have been estimated by the maximization of conditional probability of earthquake occurrence. Pareto distribution shows the highest conditional probability compared to other distribution although it shows the lowest recurrence time compared to others. Rayleigh shows the lowest conditional probability, and Exponential shows intermediate probabilities in between Weibull and Pareto distributions. Specified four typical probability density models have been validated with the predicted event in Eastern Himalayan and Naga Thrust for earthquake Mw ≥ 5.5 recorded event. [ABSTRACT FROM AUTHOR]

Kanpur City and Allahabad City are the most populous city and the largest urban agglomeration among other north Indian cities. Both the cities are situated along Ganga and Yamuna River. The study areas are one of the growing urban centers in Northern India. Two large Himalayan earthquakes experienced by this area during 1803 A.D. and 1934, and large-scale liquefaction was reported in and around the area along with the recent 2015 Gorkha earthquake which caused severe shaking. As per the IS-1893–2002, the study area lies in seismic zone III and the soils from the above cities are prone to liquefaction. However, no such attempt has been made so far for the detailed liquefaction potential map for the study area. The present study is an approach towards evaluation and preparation of spatial distribution map of liquefaction potential for the Kanpur City and Allahabad City using several bore hole data collected from the study area. The PGA used for the liquefaction potential analysis was taken from the ground response analysis of Kanpur soil and Allahabad soil. The PGA values are 0.25 and 0.18 g for Kanpur soil and Allahabad soil respectively. The results are presented in the form of factor of safety contour map at a depth of 7, 15, 24 and 30 m below the ground surface. The map indicates that most of the sites in Kanpur City and Allahabad City area are susceptible to liquefaction and hence this aspect has to be considered in earthquake-resistant design of foundations/structures in Kanpur City and Allahabad City. [ABSTRACT FROM AUTHOR]

Sequential cumulative moment release data of macroearthquakes (Mw≥4.3) of seventeen seismic zones (A to Q) belonging to NE-Himalaya, Burmese-Andaman arc and West- Sunda arc are analysed by Hurst analysis, a non-parametric statistical procedure to identify clustering of low and high values in a time series. The moment release in a zone occurs in alternate positive, negative and positive sloping segments forming a wave like pattern with intervening small horizontal segment. The negative sloping segments indicate decelerated moment release pattern or temporal slackening of elastic strain release with high b-value (>0.95). The horizontal segment indicates temporal clustering of moderate magnitude events/seismic moments with moderate b-values (0.8-0.95). The positive segment is characterised by accelerated moment release within a short span of time indicating temporal clustering of larger magnitude earthquakes/seismic moments and exhibit lowest b-value (<0.7). All zones attest moderate to high Hurst K values, range 0.7-0.86. The pattern in Hurst plots, specially a reversal of trend after prolong negative slope is used for earthquake prognostication in the seismic zones. Our analysis shows that most of the zones register a notable reversal of Hurst clustering trend after a prolonged negative slope which is accompanied by a major earthquake near its end. However, South Burma region (Zone-I) and Tripura fold belt and Bangladesh Plain (Zone-K) do not show any moderate or large shock around the end of the negative sloping trend in Hurst plot. Hence, these two zones can be considered more prone to produce moderate to larger earthquakes in future. [ABSTRACT FROM AUTHOR]

An earthquake forecasting model has been proposed for northeast India and surrounding region in a specified time span by exploiting the temporal and the spatial variations in the Gutenberg and Richter parameters ( a and b). The study region has been divided into grid with a grid interval of 0.1° in latitude and longitude and 14 zones for the seismic activity density and the seismicity parameters estimation, respectively, while the time span of the used earthquake catalog has been divided into time grids with a fixed time interval of 5 years. The seismic activity rate at a grid point has been estimated from seismic activity density at the grid point and seismic activity in zone comprising the grid. The normalized multivariate Gaussian mixture model is considered to estimate the seismic activity density, while seismicity parameters have been estimated using the Gutenberg and Richter relation and the method of maximum likelihood estimation. The seismic activity rates at each grid point in all time grids have been fitted to an autoregressive model of order three, and the inferred coefficients of the model has been used to forecast seismic activity rate in next time grid, e.g., in time grid from 2011 to 2015 including. [ABSTRACT FROM AUTHOR]

The Bhuj region, Kutch, India, is included in the highly seismic zonation map of India. The Kutch is a rift basin and so far has experienced three major earthquakes that are due to reverse fault mechanism, which in turn have been ascribed to compressive stresses. Origin of these stresses is considered to be due to north-south convergence of the Indian Plate with the Tibetan plate, and this has placed the entire Indian Plate under the compressive stress regime. Analysis of the stress pattern in the Bhuj region, therefore, has been carried out by extracting lineaments with the help of remote sensing data for the pre- and post-earthquake periods of 26 January 2001 earthquake. For this purpose, the area has been segmented into four sectors. The lineament frequency and the percent frequency from each sector and also for the whole area have been worked out. Resolution of stress on the principle of triaxial ellipsoid has been worked out for each sector and also for the whole area. There results a temporal change in the stress pattern in each sector and also for the whole area. However, the direction of horizontal maximum compressive stress for the whole area appears to be in N 10°E in the pre-earthquake period that has changed to N 10°W in the post-earthquake period. Thus, temporal change in the horizontal maximum compressive stress direction as N 23°E, inferred by Gowd et al. (J Geophy Res 97:11879-11888, to N 10°E prior to and N 10°W in the post-earthquake period, as inferred from lineament analysis and near parallelism of the lineament maxima with that of the North Kathiawar Fault and the Chambal Jamnagar Lineament along with the longer axis of the isoseismals of the Bhuj 2001 earthquake indicates a modification in the structural fabric of the region as well as a possibility of development of a major plane of weakness. [ABSTRACT FROM AUTHOR]

In this study, an assessment of seismicity parameters in the northwest Himalaya and adjoining regions using an earthquake catalog from India Meteorological Department covering a period from June 1, 1998 to June 30, 2011 has been carried out. The spatial distributions of seismicity parameters, namely magnitude of completeness, M, a value, b value, and correlation fractal dimension, D, are estimated for the studied region. The M, a, and b values are found to be 2.5, 4.601, and 0.83, respectively. Despite significant gaps, the spatial distributions of a and b values are seen to follow similar trend and are found scattering in between Main Boundary Thrust (MBT) and South Tibet Detachment, adjoining areas of Mahendragarh-Dehradun Fault (MDF), Delhi-Haridwar Ridge (DHR) and Moradabad Fault (MF), and the southern flank of Karakoram Fault and Indus-Tsangpo Suture Zone. The estimated spatial distribution of b and a values is within 90 % of confidence level, thereby indicating non-uniform stress accumulation or higher rock fracturing density in the studied region caused by strong tectonization following several earthquakes. Negative correlation between low b value and high D is observed predominantly in the region between the MBT and Munsiari Thrust or Main Central Thrust-I of Garhwal and Kumaon Himalaya, adjoining zones of MDF, DHR, and MF of Indo-Gangetic plain, and the eastern flank of the studied region, suggesting the presence of asperities in the zone. At the same time, active creeping process can be inferred in between the MBT and Main Central Thrust of Garhwal Himalaya and the surrounding areas of Shimla region of the Himalayan arc to the northwestern part of the studied region from the positive correlation between b value and D. The results indicate that the structural heterogeneity caused by different stress accumulation and rock fracturing densities exists due to continuous tectonic adjustments between different geomorphic features of the studied region. An attempt has also been made to classify the studied region into smaller seismic zones by observing the spatial patterns of b value and D that are fractal properties of the observed seismicity, along with the prevalent fault networks. [ABSTRACT FROM AUTHOR]

- Analysis of the Koyna-Warna earthquake catalog (1968-1996) shows that on an average there is a positive correlation between thebvalue (decrease) and fractal dimensions (decrease in bothD2s and D2t) of earthquake epicenters 0.5 and 2.5 years prior to 1973 (M5.2) and 1980 (M5.5) events, respectively, except a negative correlation for about five years (1988-1993) prior to the 1993/1994 sequence (M5.4). This positive correlation indicates a weaker clustering, or that the epicenters tend to fill the two-dimensional plane. While the origin of the negative correlation seems to be that during periods of large events (lowbvalue), there is strong clustering around the main shock epicenter (high fractal dimension). Interestingly, during the last year (1995-1996) of the studied period both thebvalue and correlation dimensions rose significantly, suggesting that stress release occurs through increased levels of low magnitude and increasingly scattered seismicity, suggesting an increased risk of larger magnitude events. Incidentally, during 2000 three earthquakes of magnitudeM= 5.0, one earthquake ofM4.0, 45 earthquakes of magnitudeM3.0-3.9, and several thousand earthquakes ofM<3 have occurred in the region. Thus it can be inferred that at local scales the relationship yields both positive and negative correlation that appears to be controlled by different modes of failure within the active fault complex. [ABSTRACT FROM AUTHOR]