HR: 08:00h
AN: T11F-01 INVITED     [Abstracts]
TI: Site Characterization for the San Andreas Fault Observatory at Depth
AU: * Hickman, S H
EM: hickman@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025 United States
AU: Zoback, M D
EM: zoback@pangea.stanford.edu
AF: Stanford University, Department of Geophysics, Stanford, CA 94305 United States
AU: Ellsworth, W L
EM: ellsworth@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., MS 977, Menlo Park, CA 94025 United States
AB: The San Andreas Fault Observatory at Depth (SAFOD) is a comprehensive project to obtain rock and fluid samples, make in situ measurements, and install a permanent geophysical observatory in an inclined borehole crossing the San Andreas Fault Zone to a depth of 3.2 km. SAFOD is located near the town of Parkfield in central California, along a segment of the fault that fails through a combination of aseismic creep and regularly recurring microearthquakes. By passing through or very close to the rupture patch for a repeating magnitude 2 earthquake, SAFOD will present a unique opportunity to study the physical and chemical processes controlling earthquake generation and determine the composition, physical properties and mechanical behavior of an active, plate-bounding fault at depth. SAFOD is one element of the National Science Foundation's new EarthScope initiative (see www.earthscope.org). Drilling of SAFOD began in the summer of 2004, and will be completed in 2007. Since the SAFOD project was first proposed about 12 years ago, a wide variety of geophysical and geological investigations have been carried out in the region surrounding the SAFOD site. These studies include high-resolution seismic reflection and refraction profiles conducted through the SAFOD site and across the San Andreas Fault in 1998, 2002 and 2003, airborne and ground-based gravity and magnetic surveys, thermal and geochemical studies in shallow wells, geologic mapping, magnetotelluric profiling, microearthquake relocations, 3-D seismic tomography and fault-zone guided wave studies. These investigations were supplemented by drilling and testing of a 2.2-km-deep pilot hole at the SAFOD site in the summer of 2002, which was then instrumented with a 32-level, 3-component seismic array. This comprehensive suite of investigations surrounding the SAFOD site and in the pilot hole achieved a number of critical milestones. These include improving the location accuracy for the repeating microearthquakes being targeted by SAFOD and better defining the overall structure and geophysical setting of the San Andreas Fault Zone at Parkfield. These investigations are also providing critical information on the locations of secondary fault zones and velocity discontinuities that were used to design the current SAFOD drilling, sampling, testing and monitoring program. This geophysical and geological model is now being tested and refined as we drill toward the San Andreas Fault with SAFOD.
UR: http://www.earthscope.org
DE: 8159 Rheology--crust and lithosphere
DE: 7209 Earthquake dynamics and mechanics
DE: 7215 Earthquake parameters
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting