Collaborative Research: Linking slip dynamics to off-fault deformation in strike-slip fault systems

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The release of stored energy along large-scale faults, such as the San Andreas fault, can occur abruptly in an earthquake. But this stored energy can also be released via steady, periodic releases of energy known as "slow earthquakes", as well as through deformation in the regions around the fault. This project examines whether changes in how a fault moves or "slips" are linked to observable changes in the deformation of the regions around the fault. Physical experiments in a laboratory are used to replicate aspects of the San Andreas fault system to isolate individual factors controlling deformation and to understand the relationship between how a fault slips and where deformation occurs. Understanding how deformation is distributed between a fault itself and the surrounding regions is critical for forecasting regional earthquake hazards. This multi-institution project supports five students (high school, undergraduate, and graduate levels), and develops new computational tools for visualizing experimental results, along with curricular activities for middle school Earth Science courses.The geological motivation for this project stems from observations from central California, flanking the San Andreas fault system, where slip behavior changes along the strike of the fault, and the style of off-fault deformation appears to change near the transition in slip behavior. However, naturally deforming systems are complicated, and it is difficult to show causation between slip behavior and borderland deformation. To simplify the problem, this project incorporates a series of physical experiments in the laboratory, where boundary conditions and material properties are controlled. This approach facilitates the evaluation of (1) patterns in off-fault deformation, (2) how geologic structures develop, (3) whether the system reaches a steady-state geometry, (4) whether the rate of slip impacts patterns of deformation, and (5) whether certain structures might be diagnostic of slip control. The model results may provide guidelines for characteristic structures to look for in the borderlands of lithospheric-scale faults to demonstrate slip control of off-fault deformation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.