Estimation of source and site characteristics in the North-West Himalaya using generalized inversion method

Abstract

A site constraint generalized inversion technique (GINV) has been used in the present study to develop source and site spectra for the regions in and around north-west Himalaya. Database consists of 156 earthquake (EQ) records corresponding to 21 EQ events [2.5<magnitude <5.8], recorded at 78 recording stations. Source parameters like scalar moment( ), corner frequency( ), stress drop( ), apparent stress drop( , and seismic energy ) are computed for each EQ event by fitting the point source model to the obtained source spectra. Calculated  and  values for all events are found in the range of 4.96×10¹³Nm-2.91×10¹⁶Nm and 1.50Hz-5.50Hz respectively. Further, regression analysis between the above two parameters lead to the relation:  for the study area. Value of   computed in the study varies from 1.86×10⁸J-1.75×10¹²J. Further, value of  is found varying from 0.65MPa-21.13MPa while  is found in the range of 0.07MPa-2.76MPa. It is observed that both  and  approximately follow the theoretical relation as; = . Another outcome of the study is the site amplification curves developed based on the GINV results of horizontal and vertical components for all the recording stations. Further, site transfer function (STF) for all the recording stations characterised by the ratio of horizontal and vertical site amplification components is computed and, amplification function (A_peak) and predominant frequency (f_peak) are determined. Comparison of estimated STFs based on GINV and results of Horizontal to Vertical Spectral Ratio method (HVSR) show similarity in terms of the f_peak values.