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2008-11-10 – SEMINAR by Michael Becken: The electrical conductivity structure between the transitional (near SAFOD) and locked (SE of Cholame) segments of the San Andreas Fault, including the source region of the non-volcanic tremor.

10 November, 2008 (11:15 GMT), 5 Merrion Square, Dublin 2.

Speaker: Michael Becken (GFZ Potsdam).
Title: The electrical conductivity structure between the transitional (near SAFOD) and locked (SE of Cholame) segments of the San Andreas Fault, including the source region of the non-volcanic tremor.

Abstract:

Becken, M.1, Ritter, O.1, Bedrosian, P.2, Weckmann, U.1, 3, Munoz, G.1

1. Helmholtz Centre Potsdam – German Research Centre for Geosciences GFZ, Potsdam, Germany

2. US Geological Survey, Denver, USA

3. University of Potsdam, Institute of Geosciences, Germany

The San Andreas Fault (SAF) zone changes its mechanical behavior near Parkfield, CA, from being locked (to the SE) to a combination of a seismic creep and microseismicity (to the NW). At the transition to the creeping segment, our Magnetotelluric (MT) data suggest the existence of a fluid channel that allows for fluid migration from the upper mantle/lower crust into the upper-crustal, brittle deformation zone of the SAF. Farther to the SE near the transition to the locked segment ~ 30-50 km deep non-volcanic tremors (NVT) have been observed. Most recent seismological array observations suggest that the source region of NVT is offset from the surface trace of the SAF by about 15 km. The source region correlates spatially with an electrical conductivity anomaly within the upper mantle. However, in contrast to the situation near the creeping segment, the conductivity anomaly is isolated within the mantle, and a connection into the SAF system appears to be absent. Assuming that the conductivity anomaly in the mantle represents fluids, then these may aid in the generation of tremor episodes where the SAF is locked.