Evaluation of ground motion and site-specific response spectrum for different parts of India by the method of semi-empirical Green’s function

Abstract

A synthesis of ground motion and corresponding design response spectrum is presented here. A semi-empirical Green’s function approach based on envelope summation technique is used to model ground motion for evaluation of expected peak ground acceleration (PGA) from future large earthquake in Garhwal Himalaya, northeast (NE) and south India. The synthetic site-specific response spectra for the single degree of freedom (SDOF) structures corresponding to the synthetic ground motion records are obtained for both rock and soil conditions for engineering design of reservoir and nuclear power plant in different parts of India. The predicted PGA for NE India is found to be ~ 3.5 m/s2 at 60 km, decaying to ~ 0.1 m/s2 at 500 km distance, while it is ~ 3.0 m/s2 at 15 km, decaying to ~ 1.4 m/s2 at 80 km distance for Garhwal Himalaya. These PGA estimates are in good agreement with those obtained from the Global Seismic Hazard Assessment Program (GSHAP) exercise. The response spectrum attains its maximum relatively earlier for rock site than for soil site. The response spectra decay gradually at periods later than 0.5 s and approach asymptotically constant values at longer periods. The synthetic ground motions are used to perform seismic response analysis of engineering structures. For such analysis, a PGA of 0.027 g is estimated for the Tail pond reservoir in south India for a target earthquake of M 6.5 at 50 km distance, while a PGA of 0.015 g is found for the Gorakhpur nuclear power plant in north India for similar magnitude and distance. The difference in the PGA estimates between the two is mostly attributed to regional difference in attenuation and site response. The findings of this study are expected to facilitate the seismic design of engineered structures, safe from seismic hazard, in regions where strong motion data are sparse.