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Geophysical evidence for wedging in the San Gorgonio Pass structural knot, southern San Andreas fault zone, southern California

Langenheim, V. E. and Jachens, R. C. and Matti, J. C. and Hauksson, E. and Morton, D. M. and Christensen, A. (2005) Geophysical evidence for wedging in the San Gorgonio Pass structural knot, southern San Andreas fault zone, southern California. Geological Society of America Bulletin, 117 (11-12). pp. 1554-1572. ISSN 0016-7606. doi:10.1130/B25760.1.

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Geophysical data and surface geology define intertonguing thrust wedges that form the upper crust in the San Gorgonio Pass region. This picture serves as the basis for inferring past fault movements within the San Andreas system, which are fundamental to understanding the tectonic evolution of the San Gorgonio Pass region. Interpretation of gravity data indicates that sedimentary rocks have been thrust at least 5 km in the central part of San Gorgonio Pass beneath basement rocks of the southeast San Bernardino Mountains. Subtle, long-wavelength magnetic anomalies indicate that a magnetic body extends in the subsurface north of San Gorgonio Pass and south under Peninsular Ranges basement, and has a southern edge that is roughly parallel to, but 5–6 km south of, the surface trace of the Banning fault. This deep magnetic body is composed either of upper-plate rocks of San Gabriel Mountains basement or rocks of San Bernardino Mountains basement or both. We suggest that transpression across the San Gorgonio Pass region drove a wedge of Peninsular Ranges basement and its overlying sedimentary cover northward into the San Bernardino Mountains during the Neogene, offsetting the Banning fault at shallow depth. Average rates of convergence implied by this offset are broadly consistent with estimates of convergence from other geologic and geodetic data. Seismicity suggests a deeper detachment surface beneath the deep magnetic body. This interpretation suggests that the fault mapped at the surface evolved not only in map but also in cross-sectional view. Given the multilayered nature of deformation, it is unlikely that the San Andreas fault will rupture cleanly through the complex structures in San Gorgonio Pass.

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Hauksson, E.0000-0002-6834-5051
Additional Information:© 2005 by Geological Society of America. Manuscript received by the Society 12 November 2004; revised manuscript received 18 June 2005; manuscript accepted 11 June 2005. We are grateful to Tien Grauch and Keith Howard for insightful reviews of an earlier version of the manuscript. James Spotila, Carl Wentworth, and John Wakabayashi provided rigorous and helpful reviews that tightened both the writing and logic of the paper. E. Hauksson was supported by NEHRP/USGS Grant 04HQGR0052. This is Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California, contribution 9117.
Group:Seismological Laboratory
Funding AgencyGrant Number
Subject Keywords:San Andreas fault; wedging; gravity data; magnetic data; Banning fault; San Gorgonio Pass
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Caltech Division of Geological and Planetary Sciences9117
Issue or Number:11-12
Record Number:CaltechAUTHORS:20130220-140124798
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37027
Deposited On:20 Feb 2013 23:35
Last Modified:09 Nov 2021 23:26

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