FINDING SEISMIC VELOCITY STRUCTURE OF NORTH-WEST HIMALAYAS USING P-WAVE DATA

Abstract

The aim of this project was to measure the motion of ground in the North West Himalayas due to seismic activity, primarily, earthquakes, to ultimately arrive at seismic hazard microzonation in order to assess site effects due to ground shaking. The two factors for this assessment are amplification factor and resonance frequency. These two were estimated for different stations in North West Himalayas and the variation with site was observed. The deviation in the data can be attributed to topographical factors, depth of the soil layer and its type. Thereafter, the contours of amplification factor and resonance frequency were obtained. Primary surveys indicated the dependence of amplification factor and resonance frequency on DHR - a feature oriented transverse to the Himalayas. The proximity to DHR shows an increasing effect on the resonance frequency and decreasing effect on amplification factor For the S-wave velocity structure, different values of thickness were estimated, and used in conjunction with resonance frequency to arrive at the S wave velocity structure. Further scope of work involves resonance frequency based inversion for improvement in the estimated shear wave velocity values.