Numerical Modeling for Acoustic Scattering of 3-D Spherical Wavefronts:Implications on Near Source Basin Amplification

Abstract

To understand the complex damage pattern produced by the interaction between a 3-D sedimentary basin and 3-D spherical wavefronts, scattering of seismic waves by 3-D models due to a local point source is investigated by using the Pseuda-Spectrum method, the 3-D wavefields at different tome steps are evaluated numerically for a corner diffraction and a sediment-filled basin model. 3-D wavefronts of both models are investigated from snapshots over free surface and vertical cross-section. Numerial results show that model corners generate strong out-of-plane scattering energy which causes strong seismic energy focusing and defocusing in some specific locations. For an incident wave from a point source below the basin, the sediment-filled basin traps wave energy which propagates inward and focuses near the basin center. This energy extends to the basin bottom with decreasing amplitude. Besides, part of the incident energy is blocked by this basin, resulting in low amplitudes at the surrounding rock sites. This blocking effect is not predicted by the plane wave incidence. Comparisons are made with the results from 2-D models, and they show that the 3-D wavefronts from a point source or from in-plane scattering can be approximated by 2-D models; however, wavefronts from out-of-plane scattering cannot be reproduced.

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