Search

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]

We estimated the spectral decay parameter, kappa (κ) for the Northwest (NW) Himalaya and the Northeast (NE) Himalaya, particularly NE India, using the strong motion records obtained from accelerographs installed in these regions. We estimated κ from the horizontal as well as vertical records from 294 accelerograms (three components). It has been observed that in the NW Himalaya and NE India, the value of κ varies considerably among different sites. This may be due to the lateral heterogeneity of the crust in these regions. The estimated values of κ for the NW Himalaya and the NE India region do not vary with magnitude, which shows that κ is independent of the earthquake size. It was observed that the value of κ is more for the horizontal components as compared to vertical in both the regions. The local site conditions and tectonic regime influence the value of κ as it was found that κ is more at sites covered by alluvium than at rock sites, in both the regions. The average value of κ of horizontal and vertical components for the NW Himalaya is 0.050 ± 0.009s and 0.048 ± 0.010s, respectively. For the NE India region, the average value of κ of horizontal and vertical components is 0.0368 ± 0.0054s and 0.0334 ± 0.0091s, respectively, indicating that geological formations in the NE region are more competent (compact) and less attenuative. The high values of kappa indicate that most of the high frequency energy will be removed during strong earthquakes in these regions. The kappa values estimated for both the regions may be helpful for attenuation studies and updating hazard maps in these regions. • We estimate the spectral decay parameter, kappa (κ) for the Northwest Himalaya and the Northeast India regions using strong motion (SMA) records. • We correlate between Kappa and epicentral distance, effect of geology and V s30 in both the regions. • These Kappa values can be used to model local site-effect to constrain high frequencies in a seismological model. [ABSTRACT FROM AUTHOR]