| Summary: | 碩士 === 國立成功大學 === 地球科學系碩博士班 === 92 === After 1999 Chi-Chi earthquake, a 10 km wide and 80 km long seismogenic belt appeared with strike N20°E, and located 60 km east away from Chelungpu fault. The seismic belt is located at the geological boundary seperating east and west Central Range. We try to analyze the seismicity by using earthquake relocatons, earthquake focal mechanisms and stress inversion.
Our result shows : (1) 3 months to one year after Chi-Chi earthquake, the main horizontal compressional stress under east flank of Central Range before Chi-Chi earthquake change to vertical principal stress axes σ1 under the boundary line between the east and the west flank of Central Range. (2) one year later the stress under Central Range return to the situation before Chi-Chi earthquake.
The compression-to-extension process demonstrates stress rotation in the shallow crust under Central Range before and after Chi-Chi earthquake, and offer a modern mountain collapse model in Taiwan orogen.
Key words: Chi-Chi earthquake, mountain collapse, focal mechanisms, stress inversion.
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