The effect of fault geometry on the 1999 Chi-Chi (Taiwan) earthquake

The September 20, 1999 M 7.6 Chi-Chi (Taiwan) earthquake produced enough ne ar-source seismic data to verify many theoretical predictions of the effect s of fault geometry on the physics of the earthquake process. These effects include increased motion on the hanging wall (peaked at the fault trace), a transition from thrust to significant left-lateral slip as one proceeds n orthward on the fault, and a mismatch between the nearfield and far-field e stimates of faulting style, energy, and apparent stress. Through rigorous 3 -D dynamic models elf this earthquake, all of these features can be seen to be robust consequences of the three-dimensional, asymmetric fault geometry and its angle with the free surface of the earth. The results of this stud y imply that for dipping faults that intersect the earth's surface, many im portant features of earthquakes are controlled by the fault geometry, and i n principle might be predicted ahead of time.