Fault Connectivity Controls Synthetic Earthquake Catalogs and 30-Year Rupture Probabilities in RSQSim Simulations of the Eastern San Francisco Bay Area

Evan O. Marschall, Alice-Agnes Gabriel, Bruce E. Shaw, Jeena Yun, Albert R. Kottke, Jennifer Donahue, & Michael E. Oskin

Submitted August 30, 2026, SCEC Contribution #15332, 2026 SCEC Annual Meeting Poster #TBD

The faults of the eastern San Francisco Bay Area, California, have long been known as a source of seismic hazard. This potential for large earthquakes, paired with high population density and economic activity, leads to a high seismic risk in the Bay Area (Field et al., 2013; Petersen et al., 2023). Here, we use the quasi-static, long-term earthquake simulator RSQSim (Richards-Dinger & Dieterich, 2012) to generate an ensemble of synthetic earthquake catalogs for the region. We run a suite of models varying fault connectivity (hereafter “Connected” and “Disconnected” models), frictional behavior, and approximations of elastodynamic weakening. We compare the resulting catalogs with one another, with available paleoseismic data, and with UCERF3 time-independent (“TI”) and time-dependent (“TD”) probabilities (Field et al., 2014; 2015). We find that the fault connectivity exerts a first-order control on the simulated catalogs. Connected models yield 30-year probabilities consistent with both UCERF3 TI and TD estimates. In contrast, Disconnected models underestimate them. The Disconnected models also promote enhanced earthquake clustering along individual faults. Although our simulations match UCERF3 probabilities, no single model reproduces the average recurrence and covariance characteristics of paleoseismic records at all three sites (Mira Vista / Northern Hayward, Tyson Lagoon / Southern Hayward and Leyden Creek / Calaveras) simultaneously. This indicates that although RSQSim captures the region's statistical and probabilistic behavior, the paleoseismic record may reflect natural processes not represented in quasi-static modeling. Future work will initialize fully dynamic rupture simulations from RSQSim pre-event states to quantify how elastodynamic effects modulate individual earthquakes and event sequences.

Citation
Marschall, E. O., Gabriel, A., Shaw, B. E., Yun, J., Kottke, A. R., Donahue, J., & Oskin, M. E. (2026, 08). Fault Connectivity Controls Synthetic Earthquake Catalogs and 30-Year Rupture Probabilities in RSQSim Simulations of the Eastern San Francisco Bay Area. Poster Presentation at 2026 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)