ctive tectonics in the hanging wall area of Sanyi fault: from Chentoushan to Cholan area, Central Taiwain
Date Issued
2008
Date
2008
Author(s)
Shi, Kuo-Wei
Abstract
In the area between Chentoushan and Cholan, Central Taiwan, a series of river terraces have been developed along the northern bank of the Taan River. There are several previously proposed active structures in this area, including the Sanyi fault, Chelungpu fault i.e., (1999 Chi-Chi earthquake fault), and Chentoushan fault. By using DEM（Digital Elevation Model), aerial photographs, and field investigations, these terraces are remapped and then categorized into two groups: lateritic group and non-lateritic group to the west and east respectively. The result of detailed mapping suggests that the Chentoushan fault (CTSF) is thrust dominant rather than strike slip dominant with a fault line scarp of 70 m in height, entirely different from that of the 1935 Tuntzuchiao fault (TTCF) which is dextral strike-slip fault with a fault scarp of only 3 m. From seismic profile, a pre-existing normal fault is considered as the subsurface extension of TTCF. On the other hand, the CTSF is a branch fault, generated from the deeper part of the Sanyi fault. Based on this three-dimensional relationship and kinematic analysis, the above-mentioned two faults are not the same fault as suggested before, but only similarly oriented on the ground surface.ntegrating geomorphic feature mapping and structural profile constructed from published seismic profiles, a kinematic model of the Sanyi fault and Chentoushan fault is presented in this study. From our modeling result, the slip of Sanyi fault has reached 300 m after the formation of the terrace Lt1. Based on the riser offset of the terraces, fault slip of 116 m can be derived along Chentoushan fault. According to aerial photo analysis, the non-lateritic terraces have been tilted by Neiwan anticline and Neiwan syscline prior to the Chi-Chi earthquake; however, age data are needed in the future study to define the ages of the terraces. On the other hand, the western lateritic terraces are deformed by Sanyi and Chentoushan faults.
Subjects
Sanyi fault
Chentoushan fault
Aactive tectonics
Terrace
Type
thesis
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