Seismic Wave Propagation in Basin Structure from Numerical Modeling


A sedimentary basin can significantly effect the amplification of earthquake ground motions; however, amplification at any given site is dependant upon the locality of the earthquake¢XPs epicenter. A knowledge of basin response plays an important role in the study of probabilistic seismic hazard in basin areas. It is important to know average amplification and intrinsic variability of each site in a given basin area. To this end, we have applied the spectral element method to estimate three-dimensional seismic responses for various basin structures including: (1) a basin with heterogeneous sediments surrounded by bedrock; (2) a basin with complex topographic features at its surface; and (3) a basin with a thin near surface soft layer. Incorporating a double-couple point source, we simulate the ground motions of waves propagating through various numerical basin models. The results obtained in this study serve as a guide to expectations; in particular, they help in understanding what can occur when waves propagate through basin structures containing increasing amplification factors at sites located above the deeper parts of the basin. Another important task of this work is to test the accuracy and the stability of the spectral element method. By comparing waveforms generated by the spectral element method and the non-uniform grid spacing finite difference method developed by Pitarka (1999), we find the waveforms calculated by both methods are in remarkably good agreement; and more importantly, the main characteristics of the wavefield are well preserved.

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