Dynamic simulation of the 1999 Chi-Chi, Taiwan, earthquake

We apply a modified three-dimensional finite difference method to investigate the dynamics of the 1999 Chi-Chi earthquake. We determine the dynamic source rupture process and simulate the strong ground motions over a frequency range of 0.05-0.5 Hz. Our dynamic source model reveals that the rupture process of the Chi-Chi earthquake is much more complex than that described in the classical propagation rupture models. The Chi-Chi earthquake rupture process includes the jumping phenomenon. The northern parts on the fault plane have a longer slip duration than the southern parts. The motions on the hanging wall are larger than those on the footwall side, which is a consequence of the asymmetry of the fault with respect to the free surface. In general, the synthetics calculated by the dynamic source model agree well with the observed data. Our dynamic source model reproduces distinctive velocity pulses at stations located in the forward rupture direction and at stations close to the fault surface breaks. The apparent rupture directivity, propagating from south to north, then produces noticeably larger peak ground velocity to the north. These results demonstrate that the dynamic rupture model reproduces the main features of long-period ground motions. These results may lead to improved understanding of rupture processes accompanying large earthquakes. The dynamic modeling scheme may produce more reasonable and reliable strong ground motion predictions for assessment of seismic hazard.