SCEC Award Number 21153 View PDF
Proposal Category Collaborative Proposal (Integration and Theory)
Proposal Title Investigating the effects of absolute friction level on shallow fault dynamics
Investigator(s)
Name Organization
David Oglesby University of California, Riverside Christodoulos Kyriakopoulos University of Memphis
Other Participants Baoning Wu, Graduate Student
SCEC Priorities 4a, 2e, 1e SCEC Groups FARM
Report Due Date 03/15/2022 Date Report Submitted 03/16/2022
Project Abstract
 Earthquakes that rupture up to the Earth’s surface pose significant threats to populations in Southern California and beyond. In a full space with a symmetric fault, the level of absolute stress and friction has no effect on earthquake dynamics; it is the drop in stress that matters. However, Scala et al. (2018) show that the absolute friction level could control the dynamic rupture behavior for a shallow-buried thrust fault model, where there is feedback between normal and shear stresses. In our SCEC funded research from 2021, we use the 2D finite element method to carry out a parameter study to investigate this effect. We find that when a thrust fault is buried deeply, the absolute friction and stress level have no influence on the final slip as long as the stress drop and S are the same, as expected from full-space models. However, as the thrust fault approaches the free surface, the high absolute friction/stress models have larger static stress drop and slip than the otherwise equivalent lower friction/lower stress models. A higher coefficient of friction means that there is a greater perturbation in shear stress (due to the normal stress perturbation being multiplied by a larger number) compared to the low-friction/low stress case. For deeply buried faults, there is no normal stress perturbation, so this effect does not exist. This effect may also have implications for other fault systems in which normal stress perturbations feed back into shear stress perturbations, such as stepovers, bends, and branches.
Intellectual Merit This work provides a new perspective on how the (relatively unconstrained) stress and friction level on faults can determine their behavior. It is in line with SCEC’s broad goal of understanding the origin of ground motion from basic physical processes on faults. In particular, it shows how stress, friction, and fault geometry interact to generate faulting behavior.
Broader Impacts This work has implications for our understanding of the behavior of surface-rupturing faults and how that behavior may differ from their buried counterparts. It may also have implications for other fault systems in which normal stress perturbations feed back into shear stress perturbations, such as stepovers, bends, and branches. This work has contributed to the education of a graduate student, who designed and performed essentially all of the modeling.
Exemplary Figure Figure 2. (left panel) Slip for faults that intersect the surface. High friction and high stress drop produce higher fault slip even with the same estimated stress drop and S. (right panel) Slip for faults buried 9 km and 120 km. Faults buried only 9 km from the free surface also exhibit higher slip in the high friction/high stress case, but faults buried 120 km have no difference between the two cases of stress and friction.