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  A deep crustal fluid channel into the San Andreas Fault system near Parkfield, California

Becken, M., Ritter, O., Park, S. K., Bedrosian, P. A., Weckmann, U., Weber, M. (2008): A deep crustal fluid channel into the San Andreas Fault system near Parkfield, California. - Geophysical Journal International, 173, 2, 718-732.
https://doi.org/10.1111/j.1365-246X.2008.03754.x

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 Creators:
Becken, Michael1, 2, Author              
Ritter, Oliver1, 2, Author              
Park, S. K.2, 3, Author
Bedrosian, P. A.2, 3, Author
Weckmann, Ute1, 2, Author              
Weber, Michael1, 2, Author              
Affiliations:
12.2 Geophysical Deep Sounding, 2.0 Physics of the Earth, Departments, GFZ Publication Database, Deutsches GeoForschungsZentrum, ou_66027              
2Publikationen aller GIPP-unterstützten Projekte, Deutsches GeoForschungsZentrum, Potsdam, ou_44021              
3External Organizations, ou_persistent22              

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Free keywords: Magnetotelluric; Transform faults; Crustal structure
 DDC: 550 - Earth sciences
 Abstract: Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected.We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is locatedNEof the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal highconductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF.We further infer from the MT model that the resistive Salinian block basement to the SW of the SAFOD represents an isolated body, being 5–8 km wide and reaching to depths >7 km, in agreement with aeromagnetic data. This body is separated from a massive block of Salinian crust farther to the SW. The NE terminus of resistive Salinian crust has a spatial relationship with a near-vertical zone of increased seismic reflectivity ∼15 km SW of the SAF and likely represents a deep-reaching fault zone.

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Language(s): eng - English
 Dates: 2008
 Publication Status: Finally published
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Type: -
 Identifiers: eDoc: 11356
GFZPOF: 2.0 Geodynamik, Stoffkreisläufe und Ressourcen
DOI: 10.1111/j.1365-246X.2008.03754.x
 Degree: -

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Title: Geophysical Journal International
Source Genre: Journal, SCI, Scopus, ab 2024 OA-Gold
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Pages: - Volume / Issue: 173 (2) Sequence Number: - Start / End Page: 718 - 732 Identifier: CoNE: https://gfzpublic.gfz-potsdam.de/cone/journals/resource/journals180