HR: 08:45h
AN: T11F-04    [Abstracts]
TI: Defining the SAFOD Drilling Trajectory: Locating the Target Earthquakes
AU: * Thurber, C
EM: thurber@geology.wisc.edu
AF: UW-Madison, Geology and Geophysics 1215 W. Dayton St., Madison, WI 53706 United States
AU: Roecker, S
EM: roecks@rpi.edu
AF: Rensselaer Polytechnic Institute, Earth & Environmental Sci. 110 8th Street, Troy, NY 12180 United States
AU: Zhang, H
EM: hjzhang@geology.wisc.edu
AF: UW-Madison, Geology and Geophysics 1215 W. Dayton St., Madison, WI 53706 United States
AB: Our previous work on 3D seismic wavespeed models and earthquake locations near the SAFOD site contributed to defining the Phase I drilling plan for summer 2004. Two key results from that stage of our work were that the target earthquakes lie about a kilometer shallower than previously thought and that the SAFOD Pilot Hole, drilled vertically into a fractured granite body, was estimated to be situated several hundred meters southwest of a zone of substantially reduced seismic wavespeed. From this summer's drilling, we now know that the Pilot Hole is only about 200 meters away from the low velocity material at 2 km depth below surface. The current stage of our work involves the deployment of a dozen temporary seismic instruments around SAFOD and the execution of small shots adjacent to 6 of these sites in October-November 2004. The shots will be recorded by a geophone to be installed near the bottom of the Phase I SAFOD borehole and/or a multilevel geophone array. This will allow us to construct one or more additional "virtual earthquakes" (receiver gathers of surface shots treated as earthquakes) for testing absolute location accuracy, now at a position about a kilometer closer to the actual target earthquakes than the bottom of the Pilot Hole geophone array. We present the updated location and wavespeed model results obtained with the incorporation of the 2004 data. We also discuss a suite of tests of our absolute and relative location capability for the target region, and identify additional steps needed to reduce location uncertainties to approximately 10 meters in preparation for Phase III of SAFOD drilling, hitting the rupture patch of a magnitude 2 target earthquake.
DE: 8180 Tomography
DE: 8015 Local crustal structure
DE: 7215 Earthquake parameters
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting