SEISMIC HAZARD ANALYSIS WITH MOMENT RELEASE CONSTRAINT IN GARHWAL KUMAUN HIMALAYAS

Abstract

The Kumaun - Garhwal Himalaya is located in the most seismic active zone of Himalayan that exhibits many moderate to large size earthquake. To minimising the effect of Earthquake and destruction of important structures there is a need of seismic hazard analysis of Kumaun and Garhwal Himalaya. Due to the plate boundary motion there are more chance of rupture in this Region. For generalized applications, seismic hazard analysis can be used to prepare hazard zoning maps by estimating the strongmotion parameters for a closely spaced grid of sites. The present study provides a short but complete description of the probabilistic seismic hazard analysis (PSHA) method to map the quantity (PGA) with a uniform probability of not being exceeded due to the total expected seismicity during a specified period 0.01second. In this study eleven seismic zones are identify in and around of Kumaun Garhwal Himalaya and the entire area has been divided into 0.2°×0.2° grid size, and the hazard level has been assessed for each grid by considering the seismicity within a 300-km radius around the grid. Using the past earthquake data the seismicity for the area around each grid has been estimated by defining a and b value of the Gutenberg-Richter recurrence relationship and annual occurrence rate has been estimated by constant seismicity and seismic moment release constraints method. Uniform hazard contours for peak ground acceleration as the hazard parameter have been obtained for an exposure time of 50 years and for 90% and 98% confidence level at 0.01s natural periods using constant seismicity and moment release constraint. The trends reflected by the contours are broadly consistent with the major seismotectonic features in the region.