| dc.description.abstract | The 1999 Chi-Chi earthquake (Mw=7.6) was the largest seismic event on the Taiwan island in the recent century. It showed abundant information and provided earth scientists with a rare chance to study detailed behaviors of the earthquake fault. The Chi-Chi earthquake provided three major kinds of information: 1) surface dislocations, 2) seismograms, 3) underground rupture processes. We could use these to infer reliable seismic physics and complete seismic processes. This seismic rupture model would be important to study and to forecast earthquakes. In order to acquire a complete rupture model, detailed subsurface structures are needed. In this study, we used shallow reflection seismic method to detect subsurface structures of the middle portion of the fault, attempting to find the relationship between the structure and the rupture. The seismic sections, the CPC deep seismic sections and the geologic data are combined to interpret preliminarily seismogenic structures.
The following conclusions are obtained:
（1） The dip angles of the fault are related to the depth distribution of the structure. The smaller dip angle corresponds to the sallower structure.
（2） Five rises are found along the south-north direction of the fault surface. They affected the surface ruptures, the distribution of the strata, and the topographical development in this area.
（3） The Wufeng rise, found in this study, forms an obstacle to interfere the rupture propagation, which causes high displacements along the fault, high topographies, and the Wufeng bending of the fault surface trace.
（4） The Wufeng rise also stops the southern extension of the Kueichulin formation, which makes the merge of the Chelungpu fault and the lower Sanyi fault. This structural uplift allows the lower-density gravel (Toukoshan formation) to penetrate deep into the bottom of the hill around Wufeng, which eventually induces the lowest Bouguer gravity value (-54 mgal) in Taiwan.
（5） The shallow reflection seismic method is proved to be useful in the earthquake fault study. We used wide-spread seismic lines to overcome the difficulties when crossing the large areas. After Cooperating with drilling data and other geologic information, we may construct the 3D structure of the study area and reveal relevant relationships with the faulting behaviors during the earthquake. | en_US |