Our group is presently working on an updated kinematic rupture model for the 2004 earthquake by combining the GPS and regional waveform data set with the near-fault strong motion records and also the InSar-inferred deformation. This model will be used as a boundary condition to calculate the stress change on the fault by solving the elasto-dynamic equations of motion using a finite-difference method (e.g. Ide et al., 1997. The inferred stress change will be compared to observations of postseismic deformation and recurrence of characteristically repeating microearthquake sequences. Two of these sequences are the target sequences for the SAFOD deep borehole experiment.
Evidence of lateral velocity heterogeneity across the San Andreas fault (Michael and Eberhart-Phillips, 1991) might be an explanation for the elevated strong ground motions observed south of the epicenter. We will examine this possibility by performing finite-source simulations with 3D velocity structure to assess the impact of fault zone structure. In the longer term we will re-invert for kinematic slip parameters using 3D Green's functions.
The similarity and differences of the 2004 event to those that occurred in 1922, 1934, and 1966 is very important, and therefore we are also in the process of a reexamining the historical records for these earlier Parkfield events. With the constrained slip model for the 2004 event we will simulate motions for the various narrow band instrument types in operation at the time of the previous Parkfield earthquakes to ascertain the amount of information these waveforms carry with respect to the kinematic source process.
Berkeley Seismological Laboratory
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