Multi-criteria seismic hazard evaluation for Bangalore city, India

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 overburden thickness distribution, predominantly in the range of 5-10 m in the city, has been estimated through a sub-surface model from geotechnical bore-log data. The effective shear-wave velocity distribution, established through Multi-channel Analysis of Surface Wave (MASW) survey and subsequent data interpretation through dispersion analysis, exhibits site class D (180-360 m/s), site class C (360-760 m/s), and site class B (760-1500 m/s) in compliance to the National Earthquake Hazard Reduction Program (NEHRP) nomenclature. The peak ground acceleration has been estimated through deterministic approach, based on the maximum credible earthquake of M-W = 5.1 assumed to be nucleating from the closest active seismic source (Mandya-Channapatna-Bangalore Lineament). The 1-D site response factor, computed at each borehole through geotechnical analysis across the study region, is seen to be ranging from around amplification of one to as high as four times. Correspondingly, the predominant frequency estimated from the Fourier spectrum is found to be predominantly in range of 3.5-5.0 Hz. The soil liquefaction hazard assessment has been estimated in terms of factor of safety against liquefaction potential using standard penetration test data and the underlying soil properties that indicates 90% of the study region to be non-liquefiable. The spatial distributions of the different hazard entities are placed on a GIS platform and subsequently, integrated through analytical hierarchal process. The accomplished deterministic hazard map shows high hazard coverage in the western areas. The microzonation, thus, achieved is envisaged as a first-cut assessment of the site specific hazard in laying out a framework for higher order seismic microzonation as well as a useful decision support tool in overall land-use planning, and hazard management. (C) 2010 Elsevier Ltd. All rights reserved

Spatial variation of seismicity parameters across India and adjoining areas

An attempt has been made to quantify the variability in the seismic activity rate across the whole of India and adjoining areas (0-45N and 60-105E) using earthquake database compiled from various sources. Both historical and instrumental data were compiled and the complete catalog of Indian earthquakes till 2010 has been prepared. Region-specific earthquake magnitude scaling relations correlating different magnitude scales were achieved to develop a homogenous earthquake catalog for the region in unified moment magnitude scale. The dependent events (75.3%) in the raw catalog have been removed and the effect of aftershocks on the variation of b value has been quantified. The study area was divided into 2,025 grid points (191) and the spatial variation of the seismicity across the region have been analyzed considering all the events within 300 km radius from each grid point. A significant decrease in seismic b value was seen when declustered catalog was used which illustrates that a larger proportion of dependent events in the earthquake catalog are related to lower magnitude events. A list of 203,448 earthquakes (including aftershocks and foreshocks) occurred in the region covering the period from 250 B.C. to 2010 A.D. with all available details is uploaded in the websit

GPS, scaling exponent and past seismicity for seismic hazard assessment in Garhwal–Kumaun, Himalayan region

The world’s most geologically complex Himalayan arc is well known for its tectonic and seismic activities due to the collision of Indian and Eurasian plates. Based on these elements [global positioning system (GPS) deformation measurements, scaling exponent (D) of the tectonic elements and past seismicity] studied here can contribute to better understanding of dynamics and complexities of earthquakes occurrence in any region. In the present paper, the crustal deformation is analyzed with the 3-year campaign and continuous GPS sites data. The velocity vectors of the sites with IGS05 reference frame ranges from 35 to 50 mm/year and give strain-rate measurements up to 130 × 10−9 strain/year. Further, the study region was divided into number of blocks of 1° × 1° that gives different D value based on the presence and distribution of tectonic elements in a particular block. One of the blocks was identified with very high D value of 1.82, where the least seismic activity and extensive convergence due to strain accumulation in comparison with other blocks of higher capacity dimensional value has been observed. Particularly this block lying between latitude 29°N–30°N and longitude 79°E–80°E is considered to be the probable highest seismic hazard zone in the study area. Significance of the combined application of GPS study, scaling exponent and the characteristics of seismicity are stated as helpful methods in the identification of hazardous zone in the Eastern part of the central seismic gap in the Himalaya or in any active areas of the world