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

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...

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Bibliographic Details
Published in:Geology (Boulder) 2022-04, Vol.50 (4), p.387-391
Main Authors: Rodriguez Padilla, Alba M, Oskin, Michael E, Rockwell, Thomas K, Delusina, Irina, Singleton, Drake M
Format: Article
Language:English
Subjects:
Cajon Pass
California
Cenozoic
Earthquakes
Fault lines
Faults
finite element analysis
Finite element method
Geological faults
Geology
Holocene
lithostratigraphy
Lytle Creek Ridge Fault
Mathematical models
numerical models
paleoseismicity
Probability theory
Quaternary
Rupture
Rupturing
San Andreas Fault
San Bernardino County California
San Jacinto Fault
Seismic activity
seismicity
Seismology
Shaking
Slip
United States
upper Holocene
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Summary: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
1943-2682
DOI:10.1130/G49415.1