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Published February 2012 | Published
Journal Article Open

A New Perspective on the Geometry of the San Andreas Fault in Southern California and Its Relationship to Lithospheric Structure

  • 1. ROR icon California Institute of Technology


The widely held perception that the San Andreas fault (SAF) is vertical or steeply dipping in most places in southern California may not be correct. From studies of potential-field data, active-source imaging, and seismicity, the dip of the SAF is significantly nonvertical in many locations. The direction of dip appears to change in a systematic way through the Transverse Ranges: moderately southwest (55°–75°) in the western bend of the SAF in the Transverse Ranges (Big Bend); vertical to steep in the Mojave Desert; and moderately northeast (37°–65°) in a region extending from San Bernardino to the Salton Sea, spanning the eastern bend of the SAF in the Transverse Ranges. The shape of the modeled SAF is crudely that of a propeller. If confirmed by further studies, the geometry of the modeled SAF would have important implications for tectonics and strong ground motions from SAF earthquakes. The SAF can be traced or projected through the crust to the north side of a well documented high-velocity body (HVB) in the upper mantle beneath the Transverse Ranges. The north side of this HVB may be an extension of the plate boundary into the mantle, and the HVB would appear to be part of the Pacific plate.

Additional Information

© 2012 Seismological Society of America. 

Attached Files

Published - Fuis_et_al_BSSA_2012.pdf


We thank many colleagues for discussions, including Peter Bird, Nik Christensen, Paul Davis, Don Forsyth, Ruth Harris, Egill Hauksson, Gene Humphreys, Craig Nicholson, David Okaya, Mike Oskin, Thomas Parsons, Martin Scherwath, Brandon Schmandt, Peter Shearer, Paul Spudich, Bill Stuart, Uri ten Brink, Doug Wilson, and George Zandt. We thank Jeanne Hardebeck, Rick Blakely, Haijiang Zhang, and an anonymous reviewer for helpful reviews.


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August 19, 2023
March 13, 2024