Magnetotelluric Studies at the San Andreas Fault Zone: Implications for the Role of Fluids |
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Authors: | Michael Becken Oliver Ritter |
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Institution: | (1) GFZ German Research Centre for Geosciences, Telegrafenberg, 14473 Potsdam, Germany;(2) Present address: Institute of Geophysics, WWU, Corrensstr. 24, 48149 M?nster, Germany |
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Abstract: | Fluids residing in interconnected porosity networks have a significant weakening effect on the rheology of rocks and can strongly
influence deformation along fault zones. The magnetotelluric (MT) technique is sensitive to interconnected fluid networks
and can image these zones on crustal and upper mantle scales. MT images have revealed several prominent electrical conductivity
anomalies at the San Andreas Fault which have been attributed to the presence of saline fluids within such networks and which
have been associated with tectonic processes. These models suggest that ongoing fluid release in the upper mantle and lower
crust is closely related to the mechanical state of the crust. Where fluids are drained into the brittle crust, and where
these fluids are kept at high pressures, fault creep is supported. Fluid fluxes from deeper levels, in combination with meteoric
and crustal metamorphic fluid inflow, and in response to fault creep, leads to high-conductivity zones developing as fault
zone conductors in the brittle portion of crust. In turn, the absence of crustal fluid pathways may be characteristic for
mechanically locked segments of the fault. Here, MT models suggest that fluids are trapped at depth and kept at high pressures.
We speculate that fluids may infiltrate neighboring rocks and in their wake induce non-volcanic tremor. |
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