HR: 14:55h
AN: T23E-06    [Abstracts]
TI: Imaging the deep roots of the San Andreas Fault zone with magnetotelluric measurements
AU: * Becken, M
EM: becken@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg , Potsdam, 14473 Germany
AU: Ritter, O
EM: oritter@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg , Potsdam, 14473 Germany
AU: Park, S
EM: magneto@ucrmt.ucr.edu
AF: UC Riverside, 1432 Geology Department, Riverside, CA 92521 United States
AU: Weber, M
EM: mhw@gfz-potsdam.de
AF: GFZ Potsdam, Telegrafenberg , Potsdam, 14473 Germany
AB: In spring 2005, a huge volume of new magnetotelluric (MT) data was acquired in the vicinity of the SAFOD site near Parkfield, CA. This experiment addresses the dynamics of inter-plate transform faulting at lower crustal depths and contributes to the characterization of the SAFOD site on a regional scale. In particular, we aim to image the conductivity distribution of the deep roots of the San Andreas Fault zone (SAF). Overall, we recorded at 45 combined long-period / broad-band stations distributed in an area of 50 square km in the vicinity of the SAFOD site and an additional 41 broad-band stations along the 50 km long seismic reflection reflection profile of Hole and Ryberg. Data analysis and 2D modeling results of the new profile data together with existing data from previous experiments of Unsworth et al. (2004) and Park et al. (1991) reveal the conductivity structure of the crust from the top to the bottom. First results indicate the existence of a previously unknown, westward plunging conductor (5 ohm-m) at the transition zone between the electrically homogeneous resistive crust (>1000 ohm-m) in the west and the Franciscan Complex in the east. This conductor is spatially related to the seismicity occuring at maximum depths of 12 km. Though the depth extend of the conductor is not yet well constrained, resistivities lower than 5 ohm-m appear to be confined to the brittle crust. However, a broad zone of moderate resistivities below the SAF persists throughout the ductile crust and indicates structural weakness also at large depths.
DE: 0905 Continental structures (8109, 8110)
DE: 8110 Continental tectonics: general (0905)
DE: 8111 Continental tectonics: strike-slip and transform
SC: Tectonophysics [T]
MN: Fall Meeting 2005