Abstract
Based on paleo-reconstructions of tectonic evolution of Taiwan, on the style of deformation across the Taiwan mountain ranges, on global travel-time tomography beneath Taiwan and on the characteristics of the Chi-Chi earthquake, I propose that the last M7.6 earthquake is a “subduction earthquake” which has ruptured a segment of the plate interface between the Eurasia and the Philippine Sea. Considering this event as an interface thrust earthquake, I propose to guide the future investigations of the Taiwan Foothills with such view including ultra-deep drilling (about 5-8 km) through the ruptured fault, down-hole permanent monitoring, systematic paleoseismic studies across active faults and numerical modeling of elastic deformation of Taiwan coupled with GPS observations. The aim of these studies being the determination of the distribution, recurrence and magnitudes of earthquakes in the western part of Taiwan.
Highlights
Like in Japan 5 years ago after the M6.9 Kobe earthquake, the M7.6 Chi-Chi earthquake has urged the community - especially in Taiwan - to draw the conclusions from this dramatic event
The island of Taiwan is located at the junction between two lithospheric plates : the Eurasian plate which is mainly continental in nature, and oceanic in its southern part and the Philippine Sea plate which is mainly oceanic in nature (Fig. 2)
To the south of Taiwan, the oceanic part of the plate is subducting beneath the Philippine Sea plate causing the formation of the Luzon volcanic arc in the Philippines and small islands (Batan, Lanyu, Lutao ; Fig. 3)
Summary
Like in Japan 5 years ago after the M6.9 Kobe earthquake, the M7.6 Chi-Chi earthquake has urged the community - especially in Taiwan - to draw the conclusions from this dramatic event. The plate boundary might correspond either to a so-called "seismogenic zone" that had been ruptured during the Chi-Chi earthquake The foot of the range above the fault was uplifted by 3 meters on average, whereas northwestward displacement increases from 3 meters south of Nantou to 7 meters north of Taichung. All these preliminary studies done by various teams from Taiwan were presented and debated during the Geophysi cal Annual Meeting held in Keelung late October (28-29, 1999)
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