Electrical resistivity structure at the SAFOD site from magnetotelluric exploration

The magnetotelluric dataset collected on the San Andreas Fault at Parkfield has been re-analyzed using superior inversion algorithms that have been developed in recent years. A combination of constrained inversion, forward modeling and synthetic inversion studies are used, and show that at the SAFOD site, the low resistivity fault zone extends to a depth of 2 - 3 km. An extended zone of low resistivity east of the San Andreas Fault may be connected to the SAF at seismogenic depths. The connection increases along the SAF to the northwest and may be related to the transition from locked to creeping seismic behavior.