Collaborative Research: Integrated Experimental and Modeling Approach to Understand Controls on Subduction Zone Earthquakes

Subduction zones are regions where one of Earth’s tectonic plates dives beneath another. These regions produce the planet’s largest and deadliest earthquakes and tsunamis. Much of the hazard comes from the shallowest part of the fault where the two plates first meet. To predict hazards, researchers need to determine whether the fault is building up energy that will one day be released as an earthquake and tsunami or whether that energy is released through slow, gradual sliding. This project develops a system for distinguishing these behaviors. After a fault slips, it slowly regains strength in a process known as “healing.” Simultaneously, the motion of the tectonic plates reloads the fault with stress. This research will measure the rates of healing compared to loading to predict which faults globally build up to infrequent large earthquakes and which release stress through small events. The results can be used to interpret seafloor measurements and contribute to hazard assessments. The project will support training of multiple graduate and undergraduate students. Undergraduate participants will help design an interactive exhibit on subduction earthquakes for the Utah State University Geosciences Museum, bringing the science to the wider public. Interseismic locking fundamentally controls near-trench strain accumulation and release, the potential for coseismic slip to the trench, and tsunamigenesis. However, the offshore extent of interseismic locking along shallow subduction megathrusts and the pronounced diversity in this behavior observed globally remain poorly understood. This project tests the hypothesis that the competition between fault healing and tectonic loading can explain observed differences in shallow interseismic locking versus creep. The work integrates two core elements, laboratory frictional healing experiments and finite element modeling. The frictional healing experiments will be conducted on both synthetic fault materials and legacy drill-core samples of megathrust protolith recovered by past ocean drilling expeditions, with hold durations far exceeding the timescales of previous studies. The modeling will incorporate realistic, spatially variable elastic properties and fault geometry to rigorously quantify near-trench interseismic loading rates. These elements are brought together at four extensively studied margins (Nankai, Cascadia, Hikurangi, and Sumatra) selected as natural experiments because they host a wide range of shallow coupling and slip behaviors, and span diverse décollement lithologies, stresses, and temperatures. Paired microstructural analyses will constrain the mechanisms of frictional healing, and the integration of measured healing rates with modeled loading rates will yield testable predictions of shallow megathrust locking (or creep), recurrence intervals, and stress drops along well-characterized transects at each margin. These predictions will be evaluated against emerging, planned, and existing seafloor geodetic datasets, providing a quantitative framework through which future offshore geodetic observations can be interpreted. 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.