A multiple time window rupture model for the 1999 Chi‐Chi earthquake from a combined inversion of teleseismic, surface wave, strong motion, and GPS data

Abstract

We present the results of a comprehensive analysis of the rupture process of the 1999 Chi‐Chi, Taiwan, earthquake using a broad array of seismic as well as geodetic data, spanning a very wide frequency band. Our results indicate that the rupture was quite smooth, with the slip concentrated in a wide arcuate region north of the epicenter with very little slip to the east or south. We found a moment of 3.3 × 1027 dyn cm, which is consistent with the long‐period determinations for this earthquake. The rupture velocity is approximately 2.25 km/s and is quite uniform across the fault. We have tested both a single fault plane model as well as a composite fault model with a second E‐W striking plane to the north of the rupture to improve the fit of the geodetic data. Overall, the differences in slip distribution between the two models are negligible, but the fit to the GPS data is significantly better for the composite model, which is thus our preferred solution. This model is similar to other rupture models as far as the large‐scale features are concerned but differs for the smaller asperities that are present in other models but not as much in ours. These are usually poorly constrained, and with the use of the geodetic data we believe that there is little evidence for a significant amount of slip away from our main slip concentration.