This talk will provide an overview of drilling, sampling and down-hole measurement activities associated with the first two phases of the San Andreas Fault Observatory at Depth (SAFOD). The SAFOD is located at the transition between the creeping and locked sections of the fault, 9 km NW of Parkfield, CA, approximately half way between San Francisco and Los Angeles . A 2.1 km deep vertical pilot hole was drilled at the site in 2002. The SAFOD main borehole was drilled vertically to a depth of 1.5 km and then deviated at an average angle of 55 deg to vertical, passing beneath the surface trace of the San Andreas fault at a depth of 3.2 km. Repeating micro-earthquakes on the San Andreas define the main active fault trace at depth, as well as a secondary active fault about 250 m to the SW (i.e., closer to SAFOD).

The hole was rotary drilled; comprehensive cuttings were obtained and a real-time analysis of gases in the drilling mud was carried out. Spot cores were obtained at three depths (at casing set points) in the shallow granite and deeper sedimentary rocks penetrated by the hole, augmented by over fifty side-wall cores. Continuous coring of the San Andreas Fault Zone will be carried out in Phase 3 of the project in the summer of 2007. In addition to sampling mud gas, discrete fluid and gas samples were obtained at several depths for geochemical analysis. Real-time geophysical measurements were made while drilling through most of the San Andreas Fault Zone, and a suite of "open hole" geophysical measurements were also made over essentially the entire depth of the hole.