Heterogeneous distribution of the dynamic source parameters of the 1999 Chi‐Chi, Taiwan, earthquake

The spatial and temporal distribution of the stress on the fault plane of the 1999 Chi‐Chi, Taiwan, earthquake is calculated from kinematic inversion results using a three‐dimensional finite difference method for solving the elastodynamic equations. We analyze the relations between stress and slip for all grid positions on the fault, and use these relations to infer the friction law for the rupture. The dynamic source parameters were also determined. Our results show that for most of the points on the fault, the relation between stress and slip was consistent with the slip‐weakening law during the rupture process, especially for those points with large slip. However, consistency with the velocity‐weakening law is not clear from the observed relation between stress and slip velocity. The distributions of the dynamic parameters on the fault are very heterogeneous. The peak value of the static stress drop is ∼35 MPa. In general, high stress drop occurred in the areas with large slip. The estimated strength excesses are generally small suggesting that the tectonic shear stress had reached the level of the fault strength before the main shock. The slip‐weakening distance D c and the fracture energy G c are proportional to the final slip. The aftershock activity correlates with the spatial distribution of dynamic source parameters. Usually, the aftershocks near the fault plane are concentrated in regions with small or negative static stress drop, and there were few aftershocks in regions which had large values of critical slip‐weakening distance D c .