A Revisit to Seismic Hazard at Uttarakhand

This paper presents the seismic hazard of the state of Uttarakhand in India, located at the foothills of the seismically active Himalayan mountain ranges. In the present study, an updated catalog of earthquakes has been prepared for Uttarakhand which was homogenized into a unified moment magnitude scale after declustering of the catalog to remove aftershocks and foreshocks. Various source zones were identified in the study area to account for local variability in seismicity characteristics. The seismicity parameters were estimated for each of these source zones, which are necessary inputs into seismic hazard estimation of a region. The seismic hazard evaluation of the region based on a state-of-the art PSHA study was performed using the classical Cornell–McGuire approach with different source models and attenuation relations. The most recent knowledge of seismic activity in the region was used to evaluate the hazard, incorporating uncertainty associated with different modeling parameters as well as spatial and temporal uncertainties. The PSHA was performed with currently available data and their best possible scientific interpretation using an appropriate instrument such as the logic tree to explicitly account for epistemic uncertainty by considering alternative models. The hazard maps were produced for horizontal ground motion at the bedrock level and an attempt was done to bring the hazard at surface level using appropriate amplification factors. The maximum PHA value at bedrock level for 10% Probability of exceedance (PE) in 50 years is 0.34g and same for 2% PE in 50 years is 0.54g.