Analysis of Complex Faulting: Wavelet Transform, Multiple Datasets and Realistic Fault Geometry
<p>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 wa...
| Summary: | <p>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. </p>
<p>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. </p>
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