HR: 16:45h
AN: T24B-04 INVITED     [Abstracts]
TI: Observing the San Andreas Fault at Depth
AU: * Ellsworth, W
EM: ellsworth@usgs.gov
AF: U. S. Geological Survey, MS-977, Menlo Park, CA 94025
AU: Hickman, S
T24B-04 AF: U. S. Geological Survey, MS-977, Menlo Park, CA 94025
AU: Zoback, M
T24B-04 AF: Stanford University, Dept. Geophysics, Stanford, CA 94205
AU: Davis, E
T24B-04 AF: Pinnacle Technologies, 600 Townsend, San Francisco, CA 94103
AU: Gee, L
T24B-04 AF: University of California Berkeley, Seismo Lab, Berkeley, CA 94720
AU: Huggins, R
T24B-04 AF: Geometrics, Inc., 2190 Fortune, San Jose, CA 95131
AU: Krug, R
T24B-04 AF: Pinnacle Technologies, 600 Townsend, San Francisco, CA 94103
AU: Lippus, C
T24B-04 AF: Geometrics, Inc., 2190 Fortune, San Jose, CA 95131
AU: Malin, P
T24B-04 AF: Duke University, Earth Science, Durham, NC 27708
AU: Neuhauser, D
T24B-04 AF: University of California Berkeley, Seismo Lab, Berkeley, CA 94720
AU: Paulsson, B
T24B-04 AF: Paulsson Geophysical Serv. Inc., 1215 West Lambert, Brea, CA 92821
AU: Shalev, E
T24B-04 AF: Duke University, Earth Science, Durham, NC 27708
AU: Vajapeyam, B
T24B-04 AF: Geospace Engineering Resources International, 7334 N. Gessner, Houston, TX 77040
AU: Weiland, C
T24B-04 AF: Stanford University, Dept. Geophysics, Stanford, CA 94205
AU: Zumberge, M
T24B-04 AF: University of Califorina San Diego, IGPP, La Jolla, CA 92093
AB: Extending 4 km into the Earth along a diagonal path that crosses the divide between Salinian basement accreted to the Pacific Plate and Cretaceous sediments of North America, the main hole at the San Andreas Fault Observatory at Depth (SAFOD) was designed to provide a portal into the inner workings of a major plate boundary fault. The successful drilling and casing of the main hole in the summer of 2005 to a total vertical depth of 3.1 km make it possible to conduct spatially extensive and long-duration observations of active tectonic processes within the actively deforming core of the San Andreas Fault. In brief, the observatory consists of retrievable seismic, deformation and environmental sensors deployed inside the casing in both the main hole (maximum temperature 135 C) and the collocated pilot hole (1.1 km depth), and a fiber optic strainmeter installed behind casing in the main hole. By using retrievable systems deployed on either wire line or rigid tubing, each hole can be used for a wide range of scientific purposes, with instrumentation that takes maximum advantage of advances in sensor technology. To meet the scientific and technical challenges of building the observatory, borehole instrumentation systems developed for use in the petroleum industry and by the academic community in other deep research boreholes have been deployed in the SAFOD pilot hole and main hole over the past year. These systems included 15Hz omni-directional and 4.5 Hz gimbaled seismometers, micro-electro-mechanical accelerometers, tiltmeters, sigma-delta digitizers, and a fiber optic interferometeric strainmeter. A 1200-m-long, 3-component 80-level clamped seismic array was also operated in the main hole for 2 weeks of recording in May of 2005, collecting continuous seismic data at 4000 sps. Some of the observational highlights include capturing one of the M 2 SAFOD target repeating earthquakes in the near-field at a distance of 420 m, with accelerations of up to 200 cm/s and a static displacement of a few microns. Numerous other local events were observed over the summer by the tilt and seismic instruments in the pilot hole, some of which produced strain offsets of several nanostrain on the fiber optic strainmeter. We were fortunate to observe several episodes of non-volcanic tremor on the 80-level seismic array in May, 2005. These spatially unaliased recordings of the tremor wavefield reveal that the complex tremor time series is comprised of up-and down-going shear waves that produce a spatially stationary interference pattern over time scales of 10s of seconds. All data collected at SAFOD as part of the EarthScope project are open and freely available to all. The Northern California Earthquake Data Center at U.C. Berkeley is the principal data repository for SAFOD. The more than 2 TB of 80-level array data are also available at the IRIS DMC as an assembled data collection.
DE: 7209 Earthquake dynamics (1242)
DE: 7215 Earthquake source observations (1240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 8118 Dynamics and mechanics of faulting (8004)
SC: Tectonophysics [T]
MN: Fall Meeting 2005