Modelling of 1991 Uttarkashi and 2011 Indo-Nepal earthquakes using the modified semi-empirical technique by integrating site-specific quality factor

Abstract

Strong ground motion simulation is a reliable tool for seismic hazard assessment and mitigation of any region. The distribution of hazards during an earthquake is greatly influenced by the attenuation properties of the medium. Typically, regional attenuation characteristic is employed for strong motion simulation rather than site-specific attenuation. In the current study, the newly developed semi-empirical simulation approach is modified to use a site-specific attenuation relation. Initially, the medium attenuation characteristics are quantified by estimating frequency-dependent S-wave quality factor (Qβ(f)) at each recording station. These obtained Qβ(f) relations at each station are further utilised to estimate the regional relation for the Garhwal and Kumaon regions as (90±4)f (0.86±0.05) and (54±2)f (0.89±0.1), respectively. These values suggest that the Garhwal region is relatively less attenuative and more credible for seismic hazards compared to the Kumaon region. The Qβ(f) obtained at each recording station are further used to simulate the 1991 Uttarkashi (Mw 6.8) and 2011 Indo-Nepal (Mw 5.4) earthquakes. An improved match is perceived between the observed and simulated records with site-specific Qβ(f) values instead of regional ones. This comparison successfully validates the present modification in SET. This work provides insight into getting more realistic simulated results and explores recent trends in strong motion seismology for seismic hazard evaluation. © 2023, Indian Academy of Sciences.