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Simulations of Seismic Wave Propagation and Ground Motion Acceleration in a Basin-like Structure

Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100003, China Email: zhaozhixin{at}ccsd.org.cn

In this analysis, seismic wave propagation and ground motion acceleration in heterogeneous media are digitally simulated for both line and plane sources by using the pseudospectral method of staggered grid RFFT differentiation in order to show the complicated characteristics of ground motion distribution in a basin-like structure. We are particularly concerned with those frequencies that can cause damage to dams or buildings within the basin-like structure. The results show that the distribution of strong motion varies greatly with geological structure. The seismic energy transmitted into a sediment-filled basin-like structure from the bedrock may not reflect and refract back into the rock region under the bottom of the basin structure. The seismic energy is absorbed by the sediment and soil layers, and converted into the energy of the oscillations of the medium, with large amplitudes within the basin-like structures. The seismic wave propagating up and down within the basin structure may result in major damage to buildings and dams, both internal and external to the basin. It is perhaps the most notable characteristic of this modeling research. Interference occurring near the basin results in peak ground motions and high collapse ratios of buildings away from the earthquake fault. The interference strongly affects the distribution of maximum amplitudes of seismic waveforms in and around the basin structure. In addition to active fault and geological structural surveying, the simulation analyses suggest that a geophysical survey, including mapping the seismic velocity structure in the medium above the bedrock, is the most important task for aseismic studies and disaster mitigation. This study also demonstrates a need for shallow geophysics to image shallow structure in earthquake-prone areas.