HR: 0800h
AN: NS31A-05    [Abstracts]
TI: Seismic Images of the Complex Fault Systems in the Longitudinal Valley of Eastern Taiwan
AU: * Shih, R
EM: seirock@eq.ccu.edu.tw
AF: National ChungCheng University, 160 SanHsing, MinHsiung, Chiayi, 621, Taiwan
AU: Wu, M
EM: apg9210@eq.ccu.edu.tw
AF: National ChungCheng University, 160 SanHsing, MinHsiung, Chiayi, 621, Taiwan
AU: Lin, C
EM: lincw@moeacgs.gov.tw
AF: Central Geological Survey, 2, Lane 109, HuaHsin St., ChungHo, Taipei, 235, Taiwan
AU: Chen, W
EM: wenshan@ntu.edu.tw
AF: National Taiwan University, P.O. Box 13-318, Taipei, 106, Taiwan
AB: The longitudinal valley of eastern Taiwan is the most active fault zone situated in the Island of Taiwan at the collision boundary of two plates. The most significant fault system in the longitudinal valley is the east dipping Coastal Range fault at the eastern side of the valley. However, the other west dipping Central Range fault at the western side the valley is believed existed as well. There are outcrops of the Coastal Range fault exposed at a few locations, but none for the Central Range fault. Although there are other evidences suggest the existence of the Central Range fault, but it is more difficult to locate and trace the Central Range fault than the Coastal Range fault. The slates of the Central Range are overlaid by fluvial deposits in the longitudinal valley; several geophysical methods have been applied to delineate the Central Range fault at the shallow subsurface, but none of them shown direct evidence of the fault. Seismic reflection method was thought inappropriate for applying over the slates of the Central Range; however, the contact of slates and fluvial deposits actually becomes a remarkable target for mapping the fault. In this paper, we will show the first direct evidence of the west dipping Central Range fault by using shallow seismic reflection images. During the survey, several long shallow seismic lines were deployed as wide as possible to cross the longitudinal valley, and seismic energy was stacked around 60 times for penetrating the loose fluvial deposits. After careful data processing, the 24-fold CMP stacked seismic images show clear layering structures of the fluvial deposits in the longitudinal valley for more than 700 meters thick, the remarkable reflection from the top of slates, and the west dipping Central Range fault. In addition, the fronts of the east dipping Coastal Range fault in the valley are clearly imaged as well.
DE: 0935 Seismic methods (3025, 7294)
DE: 8010 Fractures and faults
DE: 8104 Continental margins: convergent
SC: Near-Surface Geophysics [NS]
MN: 2007 Joint Assembly