SCEC Award Number 21168 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Rupture Propagation Around the Big Bend of the San Andreas Fault: A Dynamic Rupture Modeling Case Study of the Great Earthquake of 1857
Investigator(s)
Name Organization
Julian Lozos California State University, Northridge
Other Participants
SCEC Priorities 1d, 5b, 4a SCEC Groups FARM, SAFS, CS
Report Due Date 03/15/2022 Date Report Submitted 05/13/2022
Project Abstract
The ~M7.9 San Andreas Fault Earthquake of 9 January 1857 may have been California’s largest historic earthquake. Its surface rupture extends from Cholame in the north to Wrightwood in the south, for a total length of ~350 km. Due to the sparseness of California’s population at the time, loss of life and property were minimal. Nonetheless, a modern repeat of the 1857 event would cause considerable loss over a large section of California. As such, an 1857-type event is generally considered the maximum likely event for hazard calculation and earthquake preparedness in southern California.

The 1857 rupture propagated around the Big Bend of the San Andreas. Previous dynamic rupture studies suggest that compressional bends like this can pose barriers to rupture. Consistent with this idea, paleoseismic studies show that the sections of the San Andreas on either side of the bend both rupture more frequently than the hinge of the bend does, and generally not at the same time. This suggests that the Big Bend may be an earthquake gate along the San Andreas Fault – and, in turn, that the 1857 earthquake may have been an exceptional event.

I use dynamic rupture simulations to interpret which conditions are necessary to replicate the observed rupture characteristics of the 1857 rupture. This physics-based understanding of the rupture process of one of California’s largest historic earthquakes can help finetune understanding of the conditions necessary for such an event to recur – which could have a significant impact on future rupture hazard forecasts for California.
Intellectual Merit This project easily fits into the earthquake gates research objective, in that I am looking at what conditions allowed the 1857 earthquake to propagate around the Big Bend of the San Andreas Fault, and whether the bend is persistently an earthquake gate at all.

Because this project is focused on past and potential future earthquakes on the the southern San Andreas, it also ties directly into the SCEC objective of better understanding the hazards posed by our major plate boundary faults.

Lastly, I am incorporating many of the SCEC community models (CFM, CVM, CSM) into the setup and initial conditions for these simulations, which fits with the goal of using these community research products in different types of studies.
Broader Impacts This eventual results of this work have the potential to benefit society by refining our understanding of the potential for very large earthquakes on the central and southern San Andreas Fault. Events like the 1857 earthquake have been treated as characteristic earthquakes in the past, and a lot of media describes preparing for the next San Andreas earthquake in southern California as preparing for another 1857. If my results do show that 1857 required a specific confluence of conditions and was an uncommon or exceptional event, this will not only help refine hazard forecasts that may include 1857 as characteristic, but may also help change communication to the public about what sorts of San Andreas earthquakes to prepare for.
Exemplary Figure This is still work in progress, and this is only an interim report. I am still working on the complex setup process for these simulations, and I do not have any exemplary figures yet.