Inversion of GPS data for spatially variable slip-rate on the San Andreas Fault near Parkfield, CA

We analyze GPS data collected from 1991–1998 at 35 sites near the Parkfield segment of the San Andreas Fault. Inverting the resultant site velocities for the distribution of interseismic slip-rate on the San Andreas reveals an area of low slip-rate on the fault extending from between Middle Mountain and Carr Hill to southeast of Gold Hill. This slip-rate pattern is similar to that found by Harris and Segall [1987] using trilateration data collected between 1966 and 1984. We infer a deep slip-rate (33 mm/yr) and depth of the transition between seismogenic and non-seismogenic slip (14 km) that agree better with independent geologic evidence than those found in the 1987 study. In contrast to Harris and Segall [1987], we find no evidence of fault-normal contraction.