Paleoseismic Investigation of Holocene Rupture of the South-central San Andreas Fault at Little Rock Creek Site, Los Angeles County, California
Year: 2024
Type: dissertation
Abstract: Secondary and even tertiary structures associated with the main trace of an active fault can accommodate significant amounts of slip during earthquakes as a result of strain partitioning. Rupture on these structures can pose significant risk to people and infrastructure within the relatively broad zone of strain partitioning. A better understanding of their rupture history and how much strain they accommodate is needed to better assess the risks posed by these structures. A fault-perpendicular trench was excavated across an elevated terrace and terrace riser at the Little Rock Creek site to intercept and examine branch and secondary faults on the Mojave section of the San Andreas Fault system. A total of eight faults were observed within the trench. Two thrust faults were found to dominate the trench structure with the remaining faults present in the hanging wall. Hanging wall faults are interpreted to be the result of oblique slip based on deflection of an unnamed drainage immediately west of the trench site. Post-Infrared-Infrared Stimulated Luminescence dating of sediments offset by the faults indicate that most recent rupture on these faults occurred within the Holocene (last ~11,700 years). Based on estimates of maximum dip-slip and strike-slip displacement observed, an average oblique slip-rate of 1.11 millimeters per year is estimated for secondary faults studied here. Recurrence interval for ground rupturing earthquakes on the Mojave section of the San Andreas fault is ~130 years based on work completed at the nearby Pallett Creek site. Assuming these secondary faults move with each event on the main trace of the San Andreas fault, an estimated of 13 centimeters of slip is estimated to be accommodated by these faults with ruptures on the main trace. This number could be higher if slip is not accrued with each event on the San Andreas fault. The results of this study demonstrate that branch and secondary faults occurring as a result of strain partitioning may pose a risk to people, property and infrastructure and emphasizes the need for detailed site studies to adequately evaluate the hazard of any fault trace in a major fault zone.
Author: Hawkins, Joseph R.
Language: English
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6911845941
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