Fine-scale structure of the San Andreas fault zone and location of the SAFOD target earthquakes

[1] We present results from the tomographic analysis of seismic data from the Parkfield area using three different inversion codes. The models provide a consistent view of the complex velocity structure in the vicinity of the San Andreas, including a sharp velocity contrast across the fault. We use the inversion results to assess our confidence in the absolute location accuracy of a potential target earthquake. We derive two types of accuracy estimates, one based on a consideration of the location differences from the three inversion methods, and the other based on the absolute location accuracy of ‘‘virtual earthquakes.’’ Location differences are on the order of 100–200 m horizontally and up to 500 m vertically. Bounds on the absolute location errors based on the ‘‘virtual earthquake’’ relocations are 50 m horizontally and vertically. The average of our locations places the target event epicenter within about 100 m of the SAF surface trace.