HR: 16:30h
AN: GP12B-03    [PDF]
TI: Conductivity Structure of the San Andreas Fault, Parkfield, Revisited
AU: * Park, S K
EM: magneto@ucrmt.ucr.edu
AF: Institute of Geophysics and Planetary Physics, University of California, Riverside, CA 92521 United States
AU: Roberts, J J
EM: roberts17@llnl.gov
AF: Lawrence Livermore National Laboratory, 7000 East Avenue, Livermore, CA 94551 United States
AB: Laboratory measurements of samples of sedimentary rocks from the Parkfield syncline reveal resistivities as low as 1 ohm m when saturated with fluids comparable to those found in nearby wells. The syncline lies on the North American side of the San Andreas fault at Parkfield and plunges northwestward into the fault zone. A previous interpretation of a high resolution magnetotelluric profile across the San Andreas fault at Parkfield identified an anomalously conductive (1-3 ohm m) region just west of the fault and extending to depths of 3 km. These low resistivity rocks were inferred to be crushed rock in the fault zone that was saturated with brines. As an alternative to this interpretation, we suggest that this anomalous region is actually the Parkfield syncline and that the current trace of the San Andreas fault at Middle Mountain does not form the boundary between the Salinian block and the North American plate. Instead, that boundary is approximately 1 km west and collocated with current seismicity. This work was performed under the auspices of the U.S. Department of Energy by the University of California Lawrence Livermore National Laboratory under contract W-7405-ENG-48 and supported specifically by the Office of Basic Energy Science. Additional support was provided by the U.S. Geological Survey (USGS), Department of the Interior, under USGS Award number 03HQGR0041. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.
DE: 0925 Magnetic and electrical methods
DE: 5109 Magnetic and electrical properties
DE: 8015 Local crustal structure
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting