HR: 0804h
AN: NS11E-0829    [Abstracts]
TI: Imaging the Chihshang Fault in the Longitudinal Valley of Eastern Taiwan by using the Shallow Seismic Reflection Method
AU: * Tseng, Y
EM: sei9503@eq.ccu.edu.tw
AF: National Chung Cheng University, 168 University Rd., Minhsiung, Chiayi, TW 621, Taiwan
AU: Shih, R
EM: seirock@eq.ccu.edu.tw
AF: National Chung Cheng University, 168 University Rd., Minhsiung, Chiayi, TW 621, Taiwan
AU: Chen, W
AF: National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Taipei, TW 10617, Taiwan
AB: The Longitudinal Valley of eastern Taiwan is the most active fault zone situated in the Island of Taiwan. The most significant fault system in the Longitudinal Valley is the east dipping Coastal Range faults, including the Chihshang fault and the Yuli faults at the eastern side of the valley. In this paper, we will concentrate on imaging the Chihshang fault, which strikes in the SSW direction for about 47 km. The Chihshang fault separates the Lichi Mélange of the Coastal Range from the fluvial deposits in the Longitudinal Valley at shallow depth. Although there are some outcrops of the fault exposed, retreat of fault scarp by erosion still made it difficult to trace the detailed location of the Chihshang fault. In addition, the characteristics of the Mélange of poor image made it more difficult to image the Chihshang fault. To obtain the clear boundary of the Chihshang fault, we have deployed several shallow seismic lines to cross the Lichi Mélange in the Coastal Range and the fluvial deposits in the Longitudinal Valley. Seismic source was stacked around 50 times at each shot point to obtain enough energy for penetrating into the loose deposits. The results of the 24-fold CMP stacked seismic images show clear layering structures of the fluvial deposits in the longitudinal valley for more than 400 meters thick, and the sharp termination of the reflections mark the clear boundary of the Chihshang fault. Based on the characteristics of formations and features of the structural across the seismic lines, we are able to interpret the Chihshang fault and the extension of the fault. The patterns of the subsurface structures are found generally consistent with that on surface, but the features of the subsurface at some locations are offset horizontally to the east, compared to the topography.
DE: 7200 SEISMOLOGY
DE: 8010 Fractures and faults
DE: 8015 Local crustal structure
SC: Near-Surface Geophysics [NS]
MN: 2007 Fall Meeting