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Cenozoic-Present |
1 Department of Geological Sciences, State University of New York, Binghamton, NY 13902 USA wu{at}binghamton.edu
2 Central Weather Bureau, Taipei, Taiwan
The 1999 Chi-Chi earthquake series occurred in Central Taiwan, where ongoing mountain building is most active. The pre- and post-Chi-Chi seismicity helps to clarify the internal orogenic activity. The 27 000 earthquakes from the 1993–2002 catalogues have been relocated with greater precision. By associating the seismicity with focal mechanisms, many structures inside the orogen have been mapped. Among them are a steeply dipping thrust fault in the deep crust; a 50-km-long left-lateral strike-slip fault in the south; and an Eastern Central Range NNE-striking normal fault. While the deep crustal thrust appears to contribute to the root-building, the southern strike-slip slip fault accommodates the mainshock fault motion, and the Eastern Central Range normal faulting probably occurs mainly after a major western Taiwan thrust type earthquake. Much of the Backbone Range and the Eastern Central Range were seismically quiescent before and after the Chi-Chi earthquake. The contrast in the seismicity of the Central Range and the surrounding regions implies different material behaviour in these different regimes of the orogen.
