Study of combined effects of sediment rheology and basement focusing in an unbounded viscoelastic medium using P-SV-wave finite-difference modelling

This paper consists of two parts. First, a fourth-order-accurate staggered-grid finite-difference (FD) program for simulation of P-SV-wave in viscoelastic medium is presented. The incorporated realistic damping is based on GMB-EK-model. The accuracy of program is validated by comparing computed phase-velocity and quality-factors with same based on GMB-EK-model and Futterman’s relations. The second part of paper presents the combined effects of sediment damping and synclinal basement focusing (SBT) on ground motion. The results reveal SBT focusing, mode conversion and diffraction of incident waves. The response of elastic SBT model reveals an increase of spectral amplification with increasing frequency. The viscoelastic response of SBT model reveals that a particular frequency may get largest amplification for a particular set of values for damping, focal-length and distance from tip of the SBT. This frequency-dependent amplification may explain mysterious damage reported in some past earthquakes if predominantly amplified frequency matches natural frequency of damaged structures.