SCEC Award Number 22144 View PDF
Proposal Category Individual Proposal (Integration and Theory)
Proposal Title Can asymmetric surface topography impact through-going rupture across branch fault systems?
Investigator(s)
Name Organization
Roby Douilly University of California, Riverside
Other Participants
SCEC Priorities 1d, 4a, 1e SCEC Groups FARM, SAFS, Seismology
Report Due Date 03/15/2023 Date Report Submitted 08/15/2023
Project Abstract
 One of the most important seismological challenges in Southern California is estimating the maximum probable earthquake size along the San Andreas Fault (SAF). Major earthquakes often involve multiple fault segments by propagating across geometric complexities such as branched fault systems. Numerical models of branch faults have described many factors (such as stress, fault geometry) that can affect the ability of rupture to propagate through discontinuities. However, one parameter that has not been explored on branch faults is the effect of asymmetric off-fault topography even though many branch fault systems are located in regions with asymmetric topography. A notable example is the San Andreas and Garlock fault intersection in Southern California. At this location, there is a stark contrast in topographic height across the Garlock fault and across the southern San Andreas Fault. Previous dynamic studies investigating the effect of asymmetric topography on a single fault have demonstrated that topography causes normal stress perturbations during rupture. In this work we use 3D finite element simulations to highlight the effects of topography on the rupture propagation along branch faults. We find that the normal stress perturbations caused by the asymmetric free boundary condition can results in different rupture paths when compared to a model with no topography. This suggests that although dynamic phases are smaller in magnitude than static stress changes, they could be sufficient to cause failure if the branch is weak.
Intellectual Merit Previous rupture dynamic studies have highlighted parameters such as branching angle, stress-orientation and stress heterogeneity that can affect rupture propagation across branch fault systems. However, the results from this study indicate asymmetric topography can significantly influence throughgoing rupture across geometric discontinuities. Our work will advance the science of fault dynamics in regions of geometrical complexity, especially fault branches. The results obtained in this project can be applicable to any complex fault systems located in region with asymmetric topography.
Broader Impacts This work has broader impacts on the assessment of seismic hazard along branch fault systems at locations with asymmetric topography. Branch faults are a type of geometric complexity that are often referred to as “earthquake gates”, because they can either terminate rupture or allow it to keep going. Understanding how topography can prevent or facilitate throughgoing rupture across branch faults is vital to the estimation of potential earthquake size in Southern California for example.
Exemplary Figure Figure 2: Time slices showing slip over time for two models: No topography (left) and Topo2 (right). Note the rupture only propagates onto the branch for the Topo2 model.