SCEC Award Number 15202 View PDF
Proposal Category Collaborative Proposal (Data Gathering and Products)
Proposal Title Quantifying active deformation through San Gorgonio Pass on the northern strands of the San Andreas fault
Investigator(s)
Name Organization
Michael Oskin University of California, Davis Judith Chester Texas A&M University
Other Participants Alex Morelan
SCEC Priorities 1a, 4a, 4c SCEC Groups Geology, SoSAFE, Seismology
Report Due Date 03/15/2016 Date Report Submitted 03/14/2016
Project Abstract
 We investigate the kinematics and activity of faults that transfer slip through the northern San Gorgonio Pass. Based on our fieldwork in 2014 and 2015, we find both the Mill Creek fault and the Mission Creek fault show evidence for activity through the Pass. We conclude that the Mill Creek fault is inactive through upper Raywood flat, but active through Mill Creek canyon west of its intersection with the Galena Peak fault. The Galena Peak fault connects the Mill Creek fault to the Mission Creek fault across the high topography of Yucaipa Ridge. We also conclude that the Mission Creek fault is active through the San Gorgonio Pass. However morphologic evidence of recent faulting is discontinuous between Raywood flat and Mission Creek Preserve. Subsidiary fault kinematics from Mill Creek canyon through upper Raywood Flat are consistent with distributed transfer of slip from the Mill Creek fault to the Mission Creek fault in the vicinity of the Galena Peak fault. The western Mill Creek fault, Galena Peak fault, and Mission Creek fault serve as alternative potential rupture paths to the geometrically complex and mechanically inefficient San Gorgonio Pass thrust. However none of these faults shows continuous morphologic evidence for surface rupture like that observed along the San Gorgonio Pass thrust.
Intellectual Merit Rates of active faulting and uplift through the northern San Gorgonio Pass, as well as the distributed deformation of basement between major active strands of the San Andreas fault, provide important information for modeling earthquake rupture behavior through the San Gorgonio Pass Special Fault Study Area (SFSA). The distributed and complex deformation we have documented illuminates that the northern strands of the San Andreas fault are a viable pathway for fault rupture through the San Gorgonio Pass. Continued work mapping faults and damages zones at the surface will compliment the mapping of seismic sources in the subsurface to determine the fault geometries and potential rupture paths at depth.
Broader Impacts The San Gorgonio Pass region is the most complex and enigmatic section of the San Andreas fault. Our work confirms that the Mill Creek fault and Mission Creek fault are active through portions of the Pass. Understanding how earthquake ruptures may pass through this area affects the probability assessment of strong ground motion over a wide area of southern California. In addition, this project is contributing to the education and research training of two graduate students, including one from an underrepresented group (D. Elizondo).
Exemplary Figure none submitted
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