Simulation of near source two-dimensional wave field and its application to the study of ground motion characteristics of the 1999 Chi-Chi, Taiwan earthquake

The characteristics of near source two-dimensional strong ground-motion resulting from complex fault rupture processes and velocity structures have been examined based on two-dimensional wave field modeling. To construct the two-dimensional surface seismic wave field, the synthetic seismogram of each grid space was simulated by theoretical Green's functions. Numerical experiments were constructed by testing different source parameters and velocity structures. The analysis undertaken in this study can be considered as a two-dimensional seismic waveform analysis and offered as a wider view for studying the wave propagation from a large earthquake. Results of this study provide significant-information about the temporal and spatial wave field snapshots on the near source area. It is found that the wave fields are strongly affected by the changes of fault geometries, rupture velocities and near fault seismic velocity structures. In this study, the newly developed wave field simulation procedure is applied to analyze the near source ground motion characteristics of the 1999 Chi-Chi, Taiwan earthquake. Summing up the modeling results and comparing with the observed near source wave field of the Chi-Chi earthquake, we rind that the Chelungpu fault has lower seismic velocity in the footwall than in the hanging wall, and seismic velocities of the footwall side, at least on its surface, are lower than its apparent rupture velocities.