The Chichi earthquake, 1999, and its role in the Taiwan orogen

The destructive Chichi earthquake occurred in Taiwan on 21 September 1999. This earthquake had exceptional consequences in terms of both the seismic h azard concerns that it raised in the island and the new seismotectonic and geodynamic concepts that arose concerning the Taiwan collision. This earthq uake is quite typical of the SE-NW plate convergence. It reactivated a thru st ramp at the front of the belt. The rupture trace shows typical tectonic patterns that control the distribution of the damage associated with fault slip. The importance of geological studies for earthquake mitigation purpos es is thus highlighted. Based on two examples (Chelungpu fault for locking and earthquakes, Chihshang fault for creep), the need for a better definiti on of the seismic cycle in Taiwan is highlighted. The Chichi earthquake sug gests that the average shortening velocities are of the same order at the b elt front and in the suture zone in the back of the belt. The concept of do uble convergent boundary is consequently introduced in the lithospheric mod el of Taiwan. (C) 2001 Academie des sciences/Editions scientifiques et medi cales Elsevier SAS.