The Detection of Three Active Faults on the Taoyuan Terrace, Northwestern Taiwan by Shallow Reflection Seismics



The Taoyuan terrace is located in northwestern Taiwan, and is bordered on the southeast by the fold-and-thrust belt of western Taiwan foothills and on the northwest by the Kuangying shelf. Owing to the blocking of the Kuangying shelf (a basement high), the northwestward tectonic movement has uplifted this area and induced three suspected faults (from north to south): the Shuanglienpo fault, the Yangmei fault, and the Hukou fault with increasing degrees of deformation. This paper reports on the use of the shallow seismic reflection method to examine details of the underground features of these faults and their relationship to the surrounding structures. The results show that the structural layers have been bent into curved shapes but not broken in all sections across the fault scraps. This fact strongly indicates that these faults belong to the fault scraps. This fact strongly indicates that these faults belong to the category of ¡§fault-bend-folds¡¨. A curved anticline due to a hidden ¡§blind thrust¡¨ in the fault-bent-fold system can adequately explain the observed structural variations. We believe that the Shuanglienpo fault and the Yangmei fault may not be active, because they are covered by a flat, undisturbed Pleistocene Teintzuhu formation and have low bending angles. However, the Hukou fault may still havethe potential to be active as revealed by its steep structural angles and some shallow disturbed layers. Thus, we should not completely ignore the possibility that the hidden blind-thrust under the Hukou fault could still move and trigger big earthquakes.

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