| Summary: | 博士 === 國立中正大學 === 地震研究所暨應用地球物理研究所 === 95 === The main purpose of this research is to perform a nonlinear waveform inversion to investigate the velocity structures of a basin. We have built up an efficient procedure which incorporates with parallel computing to accomplish the above goal. First, we adopted the nonlinear search algorithm to explore the parameter space and construct a velocity model to calculate the theoretical travel-time for each station. Second, we obtain acceptable models which have minimum travel-time error. Finally, these models are used to waveform simulation by adopting the numerical calculation. By minimizing the misfit between synthetic and observed seismograms, through the nonlinear search algorithm, we are able to obtain more precise velocity structures. By combining all these methods with parallel computer clusters, it allows us to perform the waveform inversion with less time consuming. In order to exam the performance of the procedure described previously, we applied it to investigate the velocity structure of the Taipei basin. Our results indicate that the average travel time error is less than the original data. More importantly, the highly agreement between the observed and the synthetic waveforms suggest the reliability of the velocity structure. The results are not only giving better understanding the complex structure beneath the Taipei basin , but also can allow us to identify waveform characteristics caused by velocity heterogeneity and topographic effect. Furthermore, the geometry of the Taipei basin can be clearly seen from the velocity profiles, such as the depth of the basin increases from east to west, where the deepest part (depth=680m) is near the west edge of the basin. By comparing with the velocity structures obtained from seismic reflection method, we believe that our approach can obtain more precise S-wave velocity structure of the Taipei basin. Thus, the velocity structures obtained from this study can serve as an initial model to invert more detailed structures of the Taipei basin for future research.
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