Site response estimation using strong motion network: A step towards microzonation of the Sikkim Himalayas

Site response in the Sikkim Himalayas is studied using digital accelerogram s recorded by a seven-station-strong-motion network, established to monitor the earthquakes in the region in an effort to microzone the area. Dependin g on the criterion that signal-to-noise ratio must be greater than or equal to 3, out of more than fifty earthquakes recorded during it-lay-August 199 9, only fifteen events are chosen for the non-reference-receiver-function-t ype estimate of the site amplification factors, Site response curves (with +/- 2 standard deviation uncertainty) at all the seven sites and the contou r maps at central frequencies 1, 3, 5,7, 9 and 11 Hz show station to statio n variation of the site factors at different frequencies, reflecting the ch anges in geologic/geotectonic/soil conditions. The nonlinearity of the site factor is also observed due to its strong frequency dependence. Results of this investigation reveal the significance of site response studies in the microzonation for seismic hazard assessment.