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Subsurface Geometry of the San Andreas Fault in Southern California: Results from the Salton Seismic Imaging Project (SSIP) and Strong Ground Motion Expectations

Fuis, Gary S. and Bauer, Klaus and Goldman, Mark R. and Ryberg, Trond and Langenheim, Victoria E. and Scheirer, Daniel S. and Rymer, Michael J. and Stock, Joann M. and Hole, John A. and Catchings, Rufus D. and Graves, Robert W. and Aagaard, Brad (2017) Subsurface Geometry of the San Andreas Fault in Southern California: Results from the Salton Seismic Imaging Project (SSIP) and Strong Ground Motion Expectations. Bulletin of the Seismological Society of America . ISSN 0037-1106. (In Press) http://resolver.caltech.edu/CaltechAUTHORS:20170705-073528849

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Abstract

The San Andreas fault (SAF) is one of the most studied strike‐slip faults in the world; yet its subsurface geometry is still uncertain in most locations. The Salton Seismic Imaging Project (SSIP) was undertaken to image the structure surrounding the SAF and also its subsurface geometry. We present SSIP studies at two locations in the Coachella Valley of the northern Salton trough. On our line 4, a fault‐crossing profile just north of the Salton Sea, sedimentary basin depth reaches 4 km southwest of the SAF. On our line 6, a fault‐crossing profile at the north end of the Coachella Valley, sedimentary basin depth is ∼2–3  km and centered on the central, most active trace of the SAF. Subsurface geometry of the SAF and nearby faults along these two lines is determined using a new method of seismic‐reflection imaging, combined with potential‐field studies and earthquakes. Below a 6–9 km depth range, the SAF dips ∼50°–60° NE, and above this depth range it dips more steeply. Nearby faults are also imaged in the upper 10 km, many of which dip steeply and project to mapped surface fault traces. These secondary faults may join the SAF at depths below about 10 km to form a flower‐like structure. In Appendix D, we show that rupture on a northeast‐dipping SAF, using a single plane that approximates the two dips seen in our study, produces shaking that differs from shaking calculated for the Great California ShakeOut, for which the southern SAF was modeled as vertical in most places: shorter‐period (T<1  s) shaking is increased locally by up to a factor of 2 on the hanging wall and is decreased locally by up to a factor of 2 on the footwall, compared to shaking calculated for a vertical fault.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1785/0120160309DOIArticle
http://www.bssaonline.org/content/early/2017/06/30/0120160309PublisherArticle
http://bssa.geoscienceworld.org/content/early/2017/06/30/0120160309PublisherArticle
ORCID:
AuthorORCID
Stock, Joann M.0000-0003-4816-7865
Additional Information:© 2017 Seismological Society of America. Manuscript received 10 October 2016. First Published on July 04, 2017. We thank land owners for their cooperation in data collection for this study, without which the Salton Seismic Imaging Project (SSIP) could not have been completed: line 4, Torres Martinez tribe, U.S. Bureau of Land Management (Palm Springs office); line 6, Palm Springs tram, U.C. Irvine, Coachella Valley Association of Governments, and City of Yucca Valley. Please refer to the extensive acknowledgments in Rose et al. (2013) for permissions and assistance we received for SSIP as a whole. We thank R. J. Blakely, W. D. Mooney, K. Knudsen, and two anonymous reviewers for helpful reviews, and numerous colleagues for discussions. SSIP was supported by National Science Foundation (NSF) Grants 0742263, 9742253, and 0927446 and funds from the U.S. Geological Survey (USGS) and Southern California Earthquake Center (SCEC).
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-0742263
NSFEAR-9742253
NSFEAR-0927446
USGSUNSPECIFIED
Southern California Earthquake Center (SCEC)UNSPECIFIED
Record Number:CaltechAUTHORS:20170705-073528849
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20170705-073528849
Official Citation:Subsurface Geometry of the San Andreas Fault in Southern California: Results from the Salton Seismic Imaging Project (SSIP) and Strong Ground Motion Expectations Gary S. Fuis, Klaus Bauer, Mark R. Goldman, Trond Ryberg, Victoria E. Langenheim, Daniel S. Scheirer, Michael J. Rymer, Joann M. Stock, John A. Hole, Rufus D. Catchings, Robert W. Graves, Brad Aagaard Bulletin of the Seismological Society of America Jul 2017, DOI: 10.1785/0120160309
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78745
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:06 Jul 2017 21:59
Last Modified:06 Jul 2017 21:59

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