Imaging fine seismic crustal structures in the active Taiwan orogen from the dense seismic array deployments
Abstract
The Taiwan orogen is a well-known active mountain range with destructive earthquakes occurring frequently. In this study, we image the subsurface of the source regions of the large earthquakes (M > 6) in the fold and thrust belts of western Taiwan and in the suture zone, Longitudinal Valley, of eastern Taiwan by using dense seismic array deployments. There were 1906 M7.1 Meishan, 2003 Mw6.8 Chengkung, 2013 Mw6.2 RuiSui, and 2016 Mw6.4 Meinong earthquakes occurred in the study regions. There were 4 deployments corresponding to the source regions of these earthquakes. We deployed 100 stations with 2-5 km spacing for 1 to 4 months. Because of these data sets, we were able to use many structural seismological methods (e.g., detecting small earthquakes, determining focal mechanisms of small earthquakes, imaging the substructures by ambient noise and travel-time tomography, etc.) to explore the seismogenic zones. Meishan earthquake occurred near Chiayi city in southwestern Taiwan and resulted in more than 300 casualties. As a result, the seismic image shows that how Meishan fault cuts through Chiayi blind thrust and the 3-D geometry of Chiayi blind thrust is revealed clearly for the first time. Recently, Meinong earthquake occurred in southern Taiwan, resulting in more than 100 casualties. Right after the earthquake occurred, we deployed 36 seismic stations around the epicenter. We performed ambient noise and travel-time tomography to image the local and regional scale substructures, respectively. Based on the results of ambient noise tomography, the low S-wave velocity pattern at 0-4 km depths correspond to the uplift region for the coseismic and interseismic period, which indicate the distribution of the mudstone in this area. The results of travel-time tomography show that the deeper structures (10-30 km depths) are related to the normal fault systems inherited from the extensional tectonics of the South China Sea opening Stage. Chengkung and RuiSui earthquakes occurred in south and north of eastern Taiwan, respectively. These two events show different characteristics of the suture zone from south to north. The results of tomography have revealed a high-velocity zone from the upper mantle to shallow crust beneath the suture zone. This anomalous structure could control the tectonic evolution of the plate boundary of Taiwan.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.S32A..03K
- Keywords:
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- 7215 Earthquake source observations;
- SEISMOLOGY;
- 7230 Seismicity and tectonics;
- SEISMOLOGY;
- 8125 Evolution of the Earth;
- TECTONOPHYSICS;
- 8194 Instruments and techniques;
- TECTONOPHYSICS