Abstract
AbstractThe Hayward fault in California's San Francisco Bay area produces large earthquakes, with the last occurring in 1868. We examine how physics‐based dynamic rupture modeling can be used to numerically simulate large earthquakes on not only the Hayward fault, but also its connected companions to the north and south, the Rodgers Creek and Calaveras faults. Equipped with a wealth of images of this fault system, including those of its 3D geology and 3D geometry, in addition to inferences about its interseismic creep‐rate pattern and rock‐friction behavior, we use a finite‐element computer code to perform 3D dynamic earthquake rupture simulations. We find that the rock properties affect the locations and amount of slip produced in our simulated large earthquakes. Crucial factors that control rupture behavior in our modeling are the earthquake nucleation locations, the fault geometry, and the data that reveal where the fault system is creeping or locked. Our findings suggest that large Rodgers Creek‐Hayward‐Calaveras‐Northern Calaveras (RC‐H‐C‐NC) fault‐system earthquakes may result from dynamic rupture that starts in a locked part of the fault system, but is then stopped by the creeping parts, leading to high‐magnitude‐6 earthquakes; or, from dynamic rupture that starts in a locked part of the fault system, then cascades through some of the creeping parts, leading to magnitude‐7 earthquakes.
Highlights
The San Andreas fault system is the primary boundary between the Pacific and NorthAmerican tectonic plates in most of California (e.g., Atwater, 1970; Wallace, 1990)
In contrast to the approach that we present in this paper, previous computational studies of large earthquakes in the San Francisco Bay region have primarily centered on kinematic
We examine the effect of including the constant of cohesion in the upper kilometers of the faults, because this is frequently done by dynamic rupture modelers to suppress large amplitude slip and slip rates and supershear rupture at the Earth’s surface
Summary
The San Andreas fault system is the primary boundary between the Pacific and NorthAmerican tectonic plates in most of California (e.g., Atwater, 1970; Wallace, 1990). In the San. Francisco Bay Area, the San Andreas fault system consists of numerous faults (Figure 1), including its namesake, the San Andreas fault. The San Andreas fault is the best known, the faults with the highest calculated likelihood of producing large earthquakes in the. San Francisco Bay Area during the years 2014-2043 are the Hayward and Rodgers Creek faults with a 33% probability of a magnitude 6.7 or larger, and the Calaveras and Northern Calaveras faults with a 26% probability (Aagaard et al, 2016, based on information from Field et al., 2013). A large earthquake on the Hayward fault alone will likely affect more than a million people and cause billions of dollars in economic losses, due to the fault's proximity to critical lifelines, homes, and businesses (e.g., Hudnut et al, 2018). Paleoseismic studies have exposed geologic features caused by 12 or more ground surface rupturing Hayward fault earthquakes, and document an average largeearthquake recurrence interval of 161+/-65 years on the southern Hayward fault for the years 91-
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