This thesis presents the studies of two recent large and well-recorded earthquakes,the 1999 Hector Mine and Chi-Chi earthquakes. A new procedure for the determinationof rupture complexity from a joint inversion of static and seismic data wasfirst developed. This procedure applies a wavelet transform to separate seismic informationrelated to the spatial and temporal slip history, then uses a simulatedannealing algorithm to determine the finite-fault model that minimizes the objectivefunction described in terms of wavelet coefficients. This method is then applied tosimultaneously invert the slip amplitude, slip direction, rise time and rupture velocitydistributions of the Hector Mine and Chi-Chi earthquakes with both seismic andgeodetic data. Two slip models are later verified with independent datasets.
Results indicate that the seismic moment of the Hector Mine earthquake is 6.28 x10^(19) Nm, which is distributed along a "Y" shape fault geometry with three segments.The average slip is 1.5 m with peak amplitudes as high as 7 m. The fault rupture hasan average slip duration of 3.5 sec and a slow average rupture velocity of 1.9 km/ sec,resulting in a 14 sec rupture propagation history. The rise time appears to be roughlyproportional to slip, and the two branches of "Y" shape fault rupture together. TheChi-Chi earthquake is the best-recorded large earthquake so far. Its seismic momentof 2.7 x 10^(20) Nm is concentrated on the surface of a "wedge shaped" block. The rupturefront propagates with a slow rupture velocity of about 2.0 km/ sec. The average slipduration is 7.2 sec. Four interesting results are obtained: (1) The sinuous fault planestrongly affects both spatial and temporal variation in slip history; (2) Long-periodpeak slip velocity increases as the rupture propagates; (3) The peak slip velocitynear the surface is in general higher than on the deeper portion of the fault plane aspredicted by dynamic modeling [e.g., Oglesby et al., 1998]; and (4) the complex faultgeometry and slip distribution are related to the two transfer zones obliquely acrossTaiwan, which separate Taiwan into three regions with different tectonic activity. The transfer zone in the north can be explained by the slab breakoff mechanism proposedby Teng et al. [2000] recently.
