BSL scientists obtained a line-source slip result for the Mw 6.0 Parkfield from the automated finite-source inversion of the Northern California Seismic System. These preliminary results are consistent with the observed aftershock zone.
The BSL inversion are based on the moment tensor solution that shows a right lateral strike-slip mechanism. Using the stations shown in blue on this map, the following image shows the line-source slip result that was obtained with an "automatic run" of the finite-source code. The slip is concentrated within 12 km NW of the hypocenter (marked as zero on the scale; note that North is to the left on this plot). The extent of slip in this model is consistent with the distribution of aftershocks.
As the following image shows, the fits for the line source model are not good. They are much worse that those obtained from the 2003 San Simeon earthquake. This is probably due to the fact that the Mw6 is smallish and the observed records don't have the strong low-pass filter due to an extended rupture process. It is interesting that the SBC and SAO sites are nearly the same distance yet the amplitude at SAO is 4 times larger. This supports the NW rupture direction hypothesis.
