Analysis of Complex Faulting: Wavelet Transform, Multiple Datasets and Realistic Fault Geometry

Citation

Ji, Chen (2002) Analysis of Complex Faulting: Wavelet Transform, Multiple Datasets and Realistic Fault Geometry. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/XYM3-4718. https://resolver.caltech.edu/CaltechTHESIS:02172012-155442347

Abstract

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 determination of rupture complexity from a joint inversion of static and seismic data was first developed. This procedure applies a wavelet transform to separate seismic information related to the spatial and temporal slip history, then uses a simulated annealing algorithm to determine the finite-fault model that minimizes the objective function described in terms of wavelet coefficients. This method is then applied to simultaneously invert the slip amplitude, slip direction, rise time and rupture velocity distributions of the Hector Mine and Chi-Chi earthquakes with both seismic and geodetic data. Two slip models are later verified with independent datasets.

Results indicate that the seismic moment of the Hector Mine earthquake is 6.28 x 10^(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 has an 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 roughly proportional to slip, and the two branches of "Y" shape fault rupture together. The Chi-Chi earthquake is the best-recorded large earthquake so far. Its seismic moment of 2.7 x 10^(20) Nm is concentrated on the surface of a "wedge shaped" block. The rupture front propagates with a slow rupture velocity of about 2.0 km/ sec. The average slip duration is 7.2 sec. Four interesting results are obtained: (1) The sinuous fault plane strongly affects both spatial and temporal variation in slip history; (2) Long-period peak slip velocity increases as the rupture propagates; (3) The peak slip velocity near the surface is in general higher than on the deeper portion of the fault plane as predicted by dynamic modeling [e.g., Oglesby et al., 1998]; and (4) the complex fault geometry and slip distribution are related to the two transfer zones obliquely across Taiwan, which separate Taiwan into three regions with different tectonic activity. The transfer zone in the north can be explained by the slab breakoff mechanism proposed by Teng et al. [2000] recently.

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