PROBABILISTIC SEISMIC HAZARD ASSESSMENT OF HIMACHAL PRADESH

Abstract

The seismic hazard assessment is concerned with the estimation of strong-motion parameters at a site for the purpose of seismic safety assessment. It involves estimation of the earthquake related phenomena such as ground shaking, fault rupture, ground failure or soil liquefaction at a site. For the reliable assessment of the seismic hazard at a site, the level of ground shaking can be characterized by various types of ground motion parameters and estimated in terms of Peak Ground Acceleration (PGA) and Spectral Acceleration (Sa). In the present study Probabilistic Seismic Hazard Analysis (PSHA) has been carried out for the state of Himachal Pradesh, which is one of the most seismically active states of India. For this purpose, the study area is divided into ten seismotectonic sources based on geology, tectonics and seismicity in and around the state of Himachal Pradesh. Using Gutenberg-Richter recurrence relationship, the seismic hazard parameters such as a, b and Magnitude of Completeness, m, has been computed for all seismotectonic sources. An Expected maximum magnitude was assigned to each source zone using Kijko's probabilistic non-parametric Gaussian'(N-P-G) approach. An attenuation model proposed by Boore and Atkinson (2008) developed for shallow crustal earthquakes using a large database of thousands of worldwide records used for estimation peak ground acceleration (PGA) and peak spectral acceleration (PSA). The PGA and PSA are estimated at the bed rock level considering two cases: i) varying b-value for each source, ii) constant b-value for each source. The estimated PGA in the state of Himachal Pradesh varies from 0.04g to 0.15g for varying b-value and varies from 0.06g to 0.23g for constant b-value, with 10% probability of exceedance in 50 years. The PSA is estimated; fall in the range of 0.028g to 0.29g and 0.11g to 0.49g at 0.1s time period for varying b-value and constant b-value with 10% probability of exceedance in 50 years respectively. The results obtained are shown in form of contour maps using ArcGIS 10 software.