HR: 0800h
AN: T51C-0699    [Abstracts]
TI: The Subsurface Images of the Chiuchiungkeng Fault in the Fold-and-Thrust Belt Area of Western Taiwan
AU: * Shih, R
EM: seirock@eq.ccu.edu.tw
AF: National ChungCheng University, 168 University Rd., Minhsiung, Chiayi, TW 600, Taiwan
AB: The deformation front at the foothills area of western Taiwan is very active and showing significant crustal deformation. From the historical reports and observed seismic data, we may expect threaten of large earthquakes in that area. The Chiuchiungkeng fault is one of the young active faults situated in that fold-and-thrust belt area. Results from geological and geomorphic surveys show that the fault is an active thrust, and the fault slips should be more than 0.55mm per year. However, the subsurface features of the fault and its total length are still not clear. In this paper, we use shallow seismic reflection method to detect the Chiuchiungkeng fault and other characteristics. The results show that the Chiuchiungkeng fault strikes from north to south extends from Hobaoshan in Yunlin County, across the Niouchou River and to the Shanchulun area in Chiayi County for 18 km, and is centered at the Meishan area. According to the seismic images and the borehole data, we may know that the fault at the both ends have been truncated by another strike-slip faults. The fault dip is about 25-degree to the east, and has a sharp and narrowed fault zone at the center area. The fault dips became smaller toward the both ends, but with different styles. Close to the north end of the Chiuchiungkeng fault, where the fault zone is very wide, more than 1 km; however, at the southern section of the fault, the fault zone is narrower and the strata on both of the hanging and footwall have the similar dip angles. The total length of the Chiuchiungkeng fault is about 18 km, and the potential earthquake magnitude related to the fault is about 6.5. In 1906, an earthquake of magnitude 7.1 shocked the Meishan area and caused very severe damages. The earthquake was thought related to the left-lateral strike-slip Meishan fault only. Combining the historical map of surface ruptures, regional subsurface structures and the high-resolution shallow seismic reflection images, we may suspect that the Chiuchiungkeng fault played a more important role in that earthquake as well.
DE: 7200 SEISMOLOGY
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
SC: Tectonophysics [T]
MN: 2007 Fall Meeting