Collaborative Research: Subduction Megathrust Rheology: The Combined Roles of On- and Off-Fault Processes in Controlling Fault Slip Behavior

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Over the past two decades, the discovery of a broad spectrum of fault slip speeds in subduction zones – from slow tectonic rate creep to episodic tremor and slip to fast earthquakes - has ignited a burgeoning new research direction focused on understanding the physical mechanisms that cause faults to slip fast or slow, and how slower slip might potentially interact with large destructive earthquakes and tsunamis. Advancing our knowledge of subduction fault and earthquake mechanics requires a quantitative and holistic investigation of the deformation behavior of the plate boundary system. The deformation of both material within the fault and the surrounding wall rocks has been shown to be a function of stress, temperature, strain rate, and rock type. At the same time, heterogeneity in the fault zone, due to variations in rock type and conditions along the fault, has emerged as a leading hypothesis to explain the occurrence of slow earthquakes and slow slip events. Therefore, quantifying the deformation behavior of subduction zone rocks has been a growing endeavor for experimentalists.Through experiments and numerical models, this research will specifically address two questions. First, how does rheology along the megathrust - and its heterogeneity - affect fault slip behavior? Second, how does inelastic deformation on- and off-fault affect strain energy accumulation and the occurrence and distribution of locking and slip? New experiments will be conducted on subduction zone rocks that are deformed under pressures and temperatures present at the depths where earthquakes begin. The experimental data will inform numerical models that can bridge scales to include heterogeneity along the fault. The net result of this work will be new quantitative insights into the roles of spatial heterogeneity and rheology in subduction systems over a range of timescales. The project will support training of early career scientists including undergraduate and graduate students, postdocs, and two early career PIs. In addition, the project will develop a modeling short course for subduction zone rheology using newly developed codes. The lessons from the short course will be made publicly available as a set of short videos that include instructions for using the codes as a pathway to maximize their accessibility.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.