Stochastic finite fault modeling of Mw 6.4 earthquake along Indo-Burmese arc and site classification of its seismic recording station

Abstract

This study simulates the strong ground motion of an earthquake having magnitude 6.4 occurred on 4 February 2011 in Indo-Burmese Arc (IBA). This earthquake recorded on seven seismic recording stations namely Jowai, Jorhat, Sibsagar, Nagaon, Guwahati, Cooch Bihar and Kokhrajhar. Also, estimation of site class performed to observe the site effects of recording stations in this study. The simulation performed on the basis of revised stochastic finite fault model with dynamic corner frequency and site class for the seismic recording station where the earthquake recorded has been estimated by using Horizontal to Vertical Spectral Ratio (HVSR) technique because modeling and simulation of ground motion majorly depend upon the recorded ground motion as well as site effects, where earthquake has been recorded. The revised well known finite source simulation program (EXSIM) used in this study becomes efficient in providing the results for small magnitude earthquake occurred at large distance. The average HVSR curves plotted for all the recording stations, providing peak frequency for all 7 sites. It is observed from the present work that simulated time histories as far as primary attributes, for example, Fourier spectra, Peak ground acceleration (PGA), Response spectra, Predominant frequency are in close concurrence with the recorded ones. The predominant frequency (fpeak) obtained from HVSR technique has been validated from existing literature for the estimation of site class for seismic recording stations. The fpeak determines the average shear wave velocity (Vs30) at depth of 30 ​m of overburden thickness which varies from 200 ​m/s to 1600 ​m/s according to Program for Excellence in Strong Motion Studies (PESMOS). Whereas, National Earthquake Hazard Reduction Program (NEHRP) provision consider the site class for Vs30 below 180 ​m/s. Due its wide range of site characterization, it has been adopted globally. Therefore, in this study, the site class obtained has been compared with the site classification scheme recommended by PESMOS, NEHRP provisions and previous literature. However, the ground motion parameters and the soil classification of the earthquake recording stations for the IBA region has not been explored yet even after seeing its severity in the past decades. Productive representation of present earthquake gives the confidence to understand and evaluate seismic danger at various parts of Indo- Burmese region from tremors of various sizes. In this study it is proposed that PESMOS site classification data should be revised because it covers wide range of soil types just into three (A, B and C type) class.