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 Pseudo-Spectrum method. The 3-D wavefields at different time steps are evaluated n111 nerically 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-sections. Numerical 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 energ)r extends to the basin b• ottom 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.

A Preliminary Study on the Measurement of Sediment Concentration in Hill-Slope Runoff with an Electrolyte Tracer

“…The acoustic method disturbs the state of water flow and hence changes hydrodynamic properties of the flow. The influence is magnified as sediment concentrations raises (Hay and Sheng 1992;Thorne et al 1993;Huang et al 1995;Thorne and Hanes 2002). Optical devices emit light and then measure the total reflected light, which is proportional to sediment concentration.…”