SCEC Award Number 10086 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Estimation of fault slip rates for the San Gorgonio Pass region, California, using a dense highprecision geodetic network.
Investigator(s)
Name Organization
Rick Bennett University of Arizona Sally McGill California State University, San Bernardino
Other Participants Mr. Joshua Spinler, PhD Student, University of Arizona
SCEC Priorities A1, A2, A3 SCEC Groups Geodesy, Geology
Report Due Date 02/28/2011 Date Report Submitted N/A
Project Abstract
 We combined results from a dense network of 36 campaign and 46 continuous
GPS stations in southern California with existing data on fault slip rates to assess the partitioning of slip rate among the San Andreas, San Jacinto, and eastern California shear zone faults. The study focused around the Eastern Transverse Ranges Province (ETR), a transition zone between the southernmost San Andreas fault and eastern California shear zone. We analyzed campaign GPS data together with available data from continuous GPS stations for the period 1994–2009. We used the GPS velocity estimates to constrain elastic block models to investigate fault‐loading rates representing four hypotheses characterized by different fault‐block geometries. Fault‐block scenarios include blocks bounded by the east‐striking left‐lateral Pinto Mountain, Blue Cut, and Chiriaco faults of the ETR; blocks bounded by a right‐lateral north‐northwest striking structure (the “Landers‐Mojave earthquake line”) that cuts obliquely across the ETR and mapped Mojave Desert faults; and combinations of these end‐member hypotheses. Each model implies significantly different active fault geometries, block rotation rates, and slip rates for ETR and ECSZ structures. All models suggest that SSAF slip rate varies appreciably along strike, generally consistent with rates derived from tectonic geomorphology and paleoseismology, with a maximum of ∼23 mm/yr right‐lateral along the southernmost Coachella Valley strand, decreasing systematically to <10 mm/yr right‐lateral through the San Gorgonio Pass region. Slip rate estimates for the San Jacinto fault are ∼12 mm/yr for all models tested. All four models fit the data equally well in a statistical sense. Qualitative comparison among models and consideration of geologic slip rates and other independent data reveals strengths and weaknesses of each model. We reported the results in the Journal of Geophysical Research. This publication is SCEC contribution 1405.
Intellectual Merit The project contributed to our understanding of crustal deformation along an important segment of the San Andreas fault. In particular the project led to improved slip rate estimates and a better understanding of the partitioning of deformation between the San Andreas fault and the ECSZ.
Broader Impacts Broader impacts of the project include support for a PhD student, Mr. Joshua Spinler.
Exemplary Figure Figure 7. Transrotation fault‐block model. Red triangles represent sites with observed velocities. White lines indicate fault block boundaries intended to represent active faults. Black lines represent select Holocene faults, for comparison with modeled faults. (a) Faults chosen for modeling. See Table 6 for fault abbreviations. (b) Comparison of the observed velocities (yellow vectors with 95% confidence error ellipses) and the velocities predicted by the fault‐block modeling (blue vectors). (c) Residual velocities (observed ‐ computed) with 95% confidence error ellipses. Note that the vectors in Figure 7 are plotted at a scale that is 2.6 times larger than those plotted in Figures 7b, 7d, 7e, and 7f. (d) Individual block motions. (e) Strike‐slip rates estimated for the model faults. Red indicates right‐lateral motion, and blue indicates left‐lateral motion. Block motions are shown with yellow arrows. (f) Tensile‐slip estimates for the model faults. Red indicates closing, and blue indicates opening.