The Influence of Fault Geometry on Shallow Frictional Sliding in Subduction Zones

Recent observations of faults in the shallow regions of subduction zones - where one tectonic plate dives under another - have revealed a variety of behaviors. These include tsunami earthquakes, shallow slow slip events, and the extension of fast coseismic slip to the seafloor. How subduction zones produce this range of fault behaviors is still poorly understood. Here, the researchers investigate the effects of fault network geometry and frictional properties on their potential ruptures. They explore whether interactions between faults and with the seafloor can generate the observed range of behaviors. They use a combination of innovative theoretical analysis and numerical simulations. The goal is to constrain the relationships between shallow fault behavior and large megathrust earthquakes. The simulation outcomes unveil gradually the mechanics of earthquakes and tsunamis. They help assessing the associated risks. The codes developed by the team are shared with the community as open source. The project also provides support for an early career scientist and training for an undergraduate student at Columbia University.

This project is focused on understanding the spatial and temporal relationships between different types of slip behavior in the shallow region of subduction zones. The researchers conduct complimentary theoretical and numerical analyses of slip on a dipping thrust fault that obeys rate and state friction. They use a new technique to include the effects of the wedge-shaped geometry that is typical of shallow subduction zones. The goal is to determine how sliding stability of the fault is controlled by interactions between frictional and elastic properties and effective stress with the wedge taper angle and distance on the fault from the trench. The team also develops and implements a numerical model for slip on a fault network in a shallow subduction zone geometry. The network consists of a main plate-interface fault with a single splay thrust fault that branches off and intersects the seafloor. The model is used to simulate sequences of slip on the fault network. A special focus is to understand how shallow fault patches can alternate between producing events with different stability characteristics, and how this behavior influences megathrust events that nucleate in the locked zone. These analyses will allow answering important questions about the slip behavior of subduction zones, including: How does fault zone geometry control the sliding stability of thrust faults? How do shallow slip events nucleate and propagate within a subduction zone fault network over multiple seismic cycles?

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.