SCEC Award Number 24201 View PDF
Proposal Category Individual Research Project (Single Investigator / Institution)
Proposal Title When does aseismic creep stop rupture propagation? A dynamic rupture modeling parameter study
Investigator(s)
Name Organization
Julian Lozos California State University, Northridge
SCEC Milestones C1,2,3-1, D1-1 SCEC Groups FARM, PBS, SDOT
Report Due Date 03/15/2025 Date Report Submitted 06/27/2025
Project Abstract
 Aseismic creep on faults is characterized by rate-strengthening friction, which means that the fault actively resists movement as slip rates increase. This resistance to coseismic rupture velocities approaching from adjacent locked fault sections suggests that the frictional behaviors associated with creep can, in and of themselves, be barriers to rupture. But because creeping sections of faults are in motion during the interseismic period, they also consistently release at least some portion of the shear stress imparted by tectonic loading. This may mean that creeping areas also have low enough shear stress to cause a rupture front to die out, even independently of their frictional conditions. Thus, understanding which combinations of frictional resistance and shear stress retention, over what length of fault patch, are able to stop versus allow throughgoing coseismic rupture is critical for evaluating hazard associated with partially creeping faults. Here, I conduct a large suite of dynamic rupture simulations on partially creeping strike-slip faults under a range of stress conditions, varying frictional resistance and stress release in creeping patches of different lengths. I find that creeping areas that are longer, have more stress release due to creep, and have stronger frictional resistance are more likely to prevent rupture from reaching the end of the fault. Faster or more energetic ruptures are also able to overcome larger and more resistant creeping patches.
Intellectual Merit This project helps advance our understanding of how aseismic creep can control rupture paths and probabilities. Now that SCEC has expanded into Northern California, where partially-creeping faults are common, understanding the hazards and behaviors associated with this part of the San Andreas system hinges at least partly on developing a better understanding of how interseismic creep affects coseismic rupture. Beyond probing these effects, I also hope the passing probabilities that will come out of this work will help inform more site-specific fault investigations, hazard assessments, and planning scenarios.
Broader Impacts The results of this work will hopefully lead to earthquake planning scenarios, which will benefit Californian people and cities across a wide range of demographics.
Additionally, funding from this project has made it more feasible for me to conduct active research during the academic year at California State University, Northridge, which is a primarily teaching-focused institution. Faculty in the CSU system typically only get teaching release when we have external research funding. Therefore, every SCEC grant to a Cal State scientist allows more people to do research, and more institutions to meaningfully participate in SCEC.
Project Participants Thus far, I (Julian Lozos) have worked on this project basically by myself. As I complete the extra simulations and move on to formulating my rupture passing probabilities, I will be discussing that process with people who have developed passing probabilities for other types of fault complexity (e.g., bends or stepovers), and with people who would use those passing probabilities in their own work.
Exemplary Figure Figure 3. Results across parameter space. Each symbol represents a single dynamic rupture simulation, corresponding to a slip pattern from Figure 2. Shaded areas represent conditions that do (blue) or do not (red) allow rupture to reach the other end of the fault, as inferred from and constrained by the simulations I did run.
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