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Joint earthquake ruptures of the San Andreas and San Jacinto Faults, California, USA

Alba M. Rodriguez Padilla, Michael E. Oskin, Thomas K. Rockwell, Irina Delusina and Drake M. Singleton
Joint earthquake ruptures of the San Andreas and San Jacinto Faults, California, USA
Geology (Boulder) (December 2021) 50 (4): 387-391


Large, multi-fault earthquakes increase the threat of strong ground shaking and reshape the probability of future events across a system of faults. Fault junctions act as conditional barriers, or earthquake gates, that stop most earthquakes but permit junction-spanning events when stress conditions are favorable. Constraining the physical conditions that favor multi-fault earthquakes requires information on the frequency of isolated events versus events that activate faults through the junction. Measuring this frequency is challenging because dating uncertainties limit correlation of paleoseismic events at different faults, requiring a direct approach to measuring rupture through an earthquake gate. We show through documentation and finite-element modeling of secondary fault slip that co-rupture of the San Andreas and San Jacinto faults (California, USA) through the Cajon Pass earthquake gate occurred at least three times in the past 2000 yr, most recently in the historic 1812 CE earthquake. Our models show that gate-breaching events taper steeply and halt abruptly as they transfer slip between faults. Comparison to independent chronologies shows that 20%-23% of earthquakes on the San Andreas and the San Jacinto faults are co-ruptures through Cajon Pass.

ISSN: 0091-7613
EISSN: 1943-2682
Serial Title: Geology (Boulder)
Serial Volume: 50
Serial Issue: 4
Title: Joint earthquake ruptures of the San Andreas and San Jacinto Faults, California, USA
Affiliation: University of California at Davis, Department of Earth and Planetary Sciences, Davis, CA, United States
Pages: 387-391
Published: 20211207
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 22
Accession Number: 2022-003988
Categories: Seismology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: NSF Grant EAR-1600087
Illustration Description: illus. incl. sect., geol. sketch map
N34°17'60" - N34°17'60", W117°28'00" - W117°28'00"
Secondary Affiliation: San Diego State University, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202204
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