| dc.description.abstract | The main fault system in the foothills of central Taiwan is the Chelungpu-Tachienshan Fault system, a series of thrust faults believed to develop along a detachment. The Chusiang Fault is located between the Chelungpu Fault and the Shuangtung Fault, with northeast-oriented. It merges southwestward into the Chelungpu Fault and extends northeastward toward the Shuangtung Fault. The 1999 Chi-Chi earthquake in central Taiwan caused surface ruptures along the Chelungpu Fault, spanning approximately 100 kilometers. According to coseismic GPS data, there were significant differences in the coseismic displacement directions across the Chusiang Fault. However, there have been no reports indicating coseismic surface deformation along the Chusiang Fault trace. Based on Taiwan′s probabilistic seismic hazard analysis, the Chusiang Fault has up to a 37% probability of experiencing a magnitude 6 earthquake within the next 50 years. To understand the reactivation risk of the Chusiang Fault, it′s essential to establish a three-dimensional geometric model of its structure. However, previous research has disputed the geometric morphology of the Chusiang Fault and struggled to connect it geometrically with the Chelungpu Fault model, thus failing to fully explain observed surface phenomena or variations in spatial layer thickness. Therefore, understanding the geometric relationship between the Chusiang Fault and surrounding structures, as well as variations in layer thickness, is crucial for the geological model.
This study employs previous geological map data, alongside geological drilling and seismic data, referencing previous structural models, coseismic GPS displacement vectors from the Chi-Chi earthquake, to establish five geological cross-sections and create a reasonable regional structural inference. Considering the thickness variation of the Kueichoulin Formation, it is inferred that a blind normal fault exists underground in the Chi-Chi area, which was active during the deposition of the Kueichoulin Formation, leading to differences in thickness between the hanging wall and footwall during the deposition of the Kueichoulin Formation.
Based on the geological cross-sections in this study, the shallow segment of the Chusiang Fault dips steeply to the east while gradually flattening at depth, connecting to the Chelungpu Fault along the same detachment. According to the regional structural inference, the development of the detachment is influenced by the blind normal fault, with varying depths along both sides of the Zhuoshui River. This subsequently affects the development of thrust faults, resulting in differing structural behaviors on the north and south banks of the Zhuoshui River. The Chusiang Fault may serve as a connecting splay between the Tachienshan Fault and the Shuangtung Fault, acting as spatial adjustment between the two faults and possibly sharing similar faulting characteristics with the Tachienshan Fault, exhibiting a left-lateral thrust fault. | en_US |