We give details of a planned new magnetotelluric (MT) experiment at Parkfield and present results of a similarly designed investigation of the Dead Sea Transform fault. MT studies have always played an important role in the investigation of the San Andreas Fault (SAF) but due to short profile lengths, they have generally focused on the geometry and nature of the upper crustal fault. Continental transform faults separate plates of lithosphere but it is still debatable if these faults cut rigid blocks as narrow shear zones or if the lower crust decouples and deforms continuously over a wide area. A geophysical transect across the Dead Sea Transform (DST) in Jordan and Israel reveals a narrow, approximately 3-5 km wide, sub-vertical zone of high electrical conductivity penetrating the lithosphere to a depth of at least 30 km. This image strongly suggests that the DST is spatially confined even in the ductile lower crust. However, the situation may be different at the SAF. Results from the brittle crust show some similarities in these major transform fault systems, but also marked differences. Field work in Parkfield will start in spring 2005 with a high resolution MT survey following the 50 km reflection / refraction seismic profile of Hole & Ryberg. Additional MT sites will be deployed along and off the main 50 km profile for areal coverage. Acquiring seismic and magnetotelluric data along a coincident profile gives the opportunity to utilize the combined imaging power of the two methods.

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Ritter, O.; Park, S. K.; Bedrosian, P. A.; Weckmann, U.; Weber, M. (2004): Imaging the Deep Roots of the San Andreas Fault and the Dead Sea Fault with Magnetotelluric Measurements. AGU 2004 Fall Meeting (San Francisco 2004), T13A-1349.