Assessing fault-slip rates in diffuse plate boundary systems such as the San Andreas fault in southern California is critical both to characterize seismic hazards and to understand how different fault strands work together to accommodate plate boundary motion. In places such as San Gorgonio Pass, the geometric complexity of numerous fault strands interacting in a small area adds an extra obstacle to understanding the rupture potential and behavior of each individual fault. To better understand partitioning of fault-slip rates in this region, we build a new set of elastic fault-block models that test 16 different model fault geometries for the area. These models build on previous studies by incorporating updated campaign GPS measurements from the San Bernardino Mountains and Eastern Transverse Ranges into a newly calculated GPS velocity field that has been removed of long- and short-term postseismic displacements from 12 past large-magnitude earthquakes to estimate model fault-slip rates. Using this postseismic-reduced GPS velocity field produces a best- fitting model geometry that resolves the long-standing geologic-geodetic slip-rate discrepancy in the Eastern California shear zone when off-fault deformation is taken into account, yielding a summed slip rate of 7.2 ± 2.8 mm/yr. Our models indicate that two active strands of the San Andreas system in San Gorgonio Pass are needed to produce sufficiently low geodetic dextral slip rates to match geologic observations. Lastly, results suggest that postseismic deformation may have more of a role to play in affecting the loading of faults in southern California than previously thought.
Research Article|
December 10, 2020
New geodetic constraints on southern San Andreas fault-slip rates, San Gorgonio Pass, California
Katherine A. Guns;
Katherine A. Guns
1
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA
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Richard A Bennett;
Richard A Bennett
1
Department of Geosciences, University of Arizona, 1040 E. 4th Street, Tucson, Arizona 85721, USA
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Joshua C. Spinler;
Joshua C. Spinler
2
Department of Earth Sciences, University of Arkansas at Little Rock, 2801 S. University, Little Rock, Arkansas 72204, USA
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Sally F. McGill
Sally F. McGill
3
Department of Geological Sciences, California State University San Bernardino, 5500 University Parkway, San Bernardino, California 92407, USA
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Geosphere (2020)
Article history
received:
31 Jan 2020
rev-recd:
26 Aug 2020
accepted:
20 Oct 2020
first online:
10 Dec 2020
Citation
Katherine A. Guns, Richard A Bennett, Joshua C. Spinler, Sally F. McGill; New geodetic constraints on southern San Andreas fault-slip rates, San Gorgonio Pass, California. Geosphere 2020; doi: https://doi.org/10.1130/GES02239.1
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