Seismic hazard scenario and attenuation model of the Garhwal Himalaya using near-field synthesis from weak motion seismometry

Abstract

In this paper, we present a seismic hazard scenario for the Garhwal region of the north-western Himalayan range, in terms of the horizontal Peak Ground Acceleration. The scenario earthquake of moment magnitude Mw 8.5 has a 10% exceedance probability over the next 50 years. These estimates, the first for the region, were calculated through a stepwise process based on: An estimation of the Maximum Credible Earthquake from the seismicity of the region and Global Seismic Hazard Assessment Program considerations, and four seismotectonic parameters abstracted from near field weak-motion data recorded at five stations installed in Chamoli District of the Garhwal region in the aftermath of the 1999 Chamoli earthquake. The latter include The frequency dependent power law for the shear wave quality factor, QS the site amplification at each station using horizontal-to-vertical-spectral ratio and generalized inversion technique source parameters of various events recorded by the array and application of the resulting relations between the scalar seismic moment M0 (dyne-cm) and moment magnitude Mw and the corner frequency, ƒc (Hz) and moment magnitude Mw to simulate spectral acceleration due to higher magnitude events corresponding to the estimated Maximum Credible Earthquake, and regional and site specific local spectral attenuation relations at different geometrically central frequencies in the low, moderate and high frequency bands.