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

Narayan J.P., Kumar V.

Acta Geophysica

2014

Vol. 62, no. 6

1214--1245

This paper consists of two parts. First, a fourth-order-accurate staggeredgrid 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.

Absorbing boundary conditions in a fourth-order accurate SH-wave staggered grid finite difference algorithm

Kumar R., Narayan J.P.

Acta Geophysica

2008

Vol. 56, no. 4

1090-1108

This article presents the implementation of two well known absorbing boundary conditions in a fourth-order accurate staggered grid SH-wave finite difference (FD) algorithm with variable grid size, in a very simplified manner. Based on simulated results, it was confirmed that the Clayton and Engquist absorbing boundary condition causes edge-reflections in case of larger angle of incidence of body waves on the model edges. The results of various numerical experiments revealed that the Israeli and Orszag sponge boundary condition is efficient enough to avoid edge-reflections for any angle of incidence of the body. We recommend the use of both the Clayton and Engquist and Israeli and Orszag absorbing boundary conditions simultaneously to avoid any edge-reflections