CAREER: Path Dependent Slip of the Shallow Subduction Megathrust

William Marsh Rice University, Houston TX

Investigators

Abstract

This project is an integrated research and education plan to study the processes generating earthquakes and tsunamis in tectonic environments like the Pacific Northwest of the United States. "Subduction zones" are tectonic plate boundaries where one plate dives beneath another. They host Earth’s largest earthquakes and tsunamis. Both hazards are controlled by the mechanical properties of the rocks present along the boundary. These properties vary regionally due to different mineralogy in the host rocks. Rocks also undergo different physical and chemical changes as they are dragged into a subduction zone. These changes affect their mechanical properties as well. Here, the team study the effects of different physical and chemical paths on the mechanical properties of subduction-zone rocks. They carry out deformation experiments on rock specimens collected in targeted plate boundaries. Results helps unveiling the behavior of faults generating megathrust earthquakes. They also allow better assessing regional hazards. This project includes support for an early-career female scientist. In addition, it promotes a 3-part education plan to train students in rock mechanics at all levels, from K-12, to undergraduate and graduate levels. The 5-year award is co-funded by NSF Geophysics, Tectonics, and Marine Geology & Geophysics programs. The shallowest extent of subduction megathrusts hosts a variety of slip modes, including tsunamigenic earthquakes. The mode of fault slip at shallow conditions is proposed to be controlled by the physical properties of the sediments and rocks along the plate boundary, as well as external conditions like pore fluid pressure and temperature. However, there is no comprehensive model for which lithologies control slip behavior. How extrinsic variables control the deformation of these lithologies is also unclear. Here, the team studies experimentally the path-dependent strength and deformation behavior of shallow subduction-zone rocks. The project has a field-based component to collect naturally deformed specimens with relevant mineralogy and microstructures. The goals of the research and education plan are: (1) to determine how changes in mineralogy and porosity, experienced by subducted sediments and basalt, promote or inhibit different slip modes; (2) to quantify how the paths that lead to elevated pore fluid pressures affect different modes of slip; (3) to launch a 3-part education plan that includes the development of a mobile teaching laboratory, that of an inquiry-based electronics course, and the integration of undergraduate students in research and teaching activities. 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.