3D Ground Response Analysis of Simplified Kutch Basin by Spectral Element Method

The damage pattern observed during the 1819 Kutch earthquake and 2001 Bhuj earthquake of magnitude Mw>7.7 in India implied the significance of the effect of Kutch basin on seismic ground motion. In the present study, the Kutch rift basin is modeled as a simplified rectangular basin of size 150km × 90km × 1.5km. The shear wave velocity of the Kutch region varies from 300m/s at the surface to 800m/s at the depth of 60m. Three-dimensional ground response analysis is carried out for the simplified Kutch basin subjected to ricker wave, using the spectral element code SPEED. The soil medium is modeled through visco-elastic soil model, where the damping is represented by Quality factor. It is found out from the numerical analysis that maximum amplification of 3.6 times occurs at the corner of the basin where interference of waves reflected from multiple edges happen. The long period structures with fundamental period in the range of 1.5-2.5s located near the basin edge are found to be significantly affected by the basin effect.