Seismogenic structure of the 1935 Hsinchu-Taichung (MGR=7.1) earthquake, Miaoli, western Taiwan
Abstract
A large earthquake (MGR 7.1) took place in Miaoli on April 21, 1935 and caused severe damage in surrounding area. The associated surface ruptures daylighted the Tuntzuchiao Fault (TTCF), trending NE between the Tachia and Taan River, and the Chihhu Fault (CHF), a separate back thrust trending N-S in the Shihtan area, which is 30 km north from the TTCF. In this study, we try to clarify the structural geometry and further identify the seismogenic structure for this event. The fold-and-thrust belt in Miaoli region is characterized by three major styles of structural interactions of thrusts and folds: the reactivated pre-existing normal faults, the low angle thrust cutting through the shallow strata, and the regional décollement at the base of the sedimentary strata in depth. The hypocenter of the 1935 mainshock is located right beneath the middle reach of the Taan River. By subsurface geology, we consider that the reactivation of the pre-existing normal fault preserved in the footwall of the Sanyi Fault may be the seismogenic structure of this earthquake. It currently performs strike-slip in character and extends to the ground surface as the TTCF in the south. Combining the surface rupture and geologic map data, we interpret the CHF as a back thrust located in between two E-W strike-slip faults at both northern and southern ends. With this clear boundary condition, we incorporate the coseismic and interseismic triangulation data and remodel the fault plane geometry of both CHF and TTCF. Despite the two recorded surface ruptures, topography shows no strong evidence to infer a long development history. Therefore we conclude the two faults are either new or with relatively long recurrence interval.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2004
- Bibcode:
- 2004AGUFM.T13F..03L
- Keywords:
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- 8000 STRUCTURAL GEOLOGY (New field;
- replaces single entry 8165);
- 8015 Local crustal structure;
- 8102 Continental contractional orogenic belts;
- 8107 Continental neotectonics;
- 8123 Dynamics;
- seismotectonics