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San Andreas Fault System in Southern California (SAFSOC)

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TASK 1 - San Andreas Fault System in Northwestern Salton Trough Region

Task leader: Jonathan Matti

Statement of Problem:
The Salton Trough is host to a number of regional fault sets. Together, these faults constitute a part of the San Andreas fault system:

(1) All known strands of the San Andreas Fault Zone traverse the northwestern Salton Trough and enter the San Gorgonio Pass (SGP) region, where they have been complexly deformed (the San Gorgonio Pass knot).

(2) Sinistral strike-slip faults of the Eastern Transverse Ranges, including especially the Pinto Mountain Fault, approach the northwestern head of the Salton Trough and interact with the SAF zone in ways that are not completely understood. empty box graphic
Fan Palms grow near a spring on the Banning fault strand of the San Andreas fault system in the Coachella Valley Preserve, southern California
Fan Palms grow near a spring on the Banning Fault strand of the San Andreas Fault system in the Coachella Valley Preserve, southern California.


(3) The West Salton Detachment system, a regional normal-fault complex recently integrated along the east flank of the Peninsular Ranges block, is an important component of the transtensional latest Miocene through Pliocene San Andreas Fault system.

Fundamental questions about the San Andreas in SGP remain controversial: Why is there a big bend in the San Andreas through SGP? When during the evolution of the San Andreas system did the big bend develop? What are the tectonic implications of the evolving landscape within the structural knot in SGP and on flanking high-relief mountain blocks? Understanding the patterns and causes of interactions among the various fault sets at the northwest head of the Salton Trough is one of the key ongoing scientific challenges in the study of the San Andreas Fault system in southern California and should help answer these and other questions Through this project, the USGS has an unprecedented opportunity to integrate these three components of the San Andreas Fault system into a coherent kinematic model for the last 6 million years or so, with emphasis on how latest Quaternary fault interactions provide a context for evaluating and mitigating real-time seismic risk.

Objectives:

Mapping objectives: new 7.5’ quadrangle maps, beginning with the Cabazon quadrangle. Topical objectives include:

(1) In collaboration with K. Kendrick (Western Earthquake Hazards Team), V. Langenheim, S. Mahan and G. Landis,
conduct strain-budget investigations for strands of the San Andreas Fault in the greater San Gorgonio Pass region, with emphasis on the integration of fault-slip history with landscape evolution.
(2) Evaluate how surface structures in the San Gorgonio Pass region support (or not) subsurface structures inferred from potential-field geophysics (with V. Langenheim).
(3) Develop a structural model for how the West Salton Detachment fault in the Santa Rosa Mountains region interacted with the San Andreas Fault during the timeframe between ~6 Ma and 1.5 Ma.
(4) Develop a structural model for how Quaternary interaction between the San Andreas and San Jacinto Fault zones led to termination of the West Salton Detachment system.

Methodology:
Research objectives are achieved through a combination of geologic mapping, structural analysis, geophysical mapping, geomorphic analysis, and geochronologic studies, accompanied by sedimentary basin investigations. The Task benefits substantially from archival 1:24,000-scale geologic mapping conducted by the USGS and by others over the last two decades (J.C. Matti, B.F. Cox, D.M. Morton, R.E. Powell, M.J. Rymer, R.V. Sharp, B.E. Erskine).

Background - See previous project websites:

Deliverable products:
(1) Geologic map and digital database of the Cabazon 7.5' quadrangle
(2) Manuscript on the West Salton Detachment Fault

Task Products:
Map, Planned: Matti, J.C., Cox, B.F., Morton, D.M., and Carson, S.E., 2011, Geologic map and digital database of the
Cabazon 7.5' quadrangle, Riverside Counties, California, version 1.0, USGS, Open-File Reports

Report, Planned: Matti, J.C., Cox, B.F., Langenheim, V.E., Morton, D.M., Erskine, B.E., King, T., Landis, G.P., Premo,
W.R, Kistler, R.W., and Budahn, J.R., 2011, Late Cenozoic structural and stratigraphic framework of the West Salton
Detachment, Santa Rosa Mountains, southern California, USGS, Scientific Investigations Report

 

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