Upgrade of a Triaxial Rock Deformation Apparatus to Measure the Rheology of Subduction Megathrusts

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Earthquakes are felt as elastic waves that shake the ground, but the cause of these waves is slip along faults kilometers beneath the surface. Not all faults produce earthquakes, however, and the reasons that some faults slip destructively in earthquakes, whereas others slip so slowly that they do not produce elastic waves are not entirely known. The faults associated with the greatest hazards are found at subduction plate boundaries, such as the Pacific Northwest of the United States. These faults create the largest earthquakes and associated tsunamis, but they are also the least understood. Whether a fault slips destructively or not is controlled by the mechanical properties of the rocks within the fault zone. This proposal will fund the upgrade of equipment that will be used to measure the mechanical properties of rocks from subduction plate boundary faults. The results of these measurements will be used to determine how the rocks present in a given region determine how the faults slip, whether in an earthquake or less destructively. The measurements made by this equipment will, therefore, contribute to improved models of seismic hazards for populous regions, such as the Pacific Northwest.The physical properties of rocks along the subduction plate boundary are thought to affect the depths of transitions between aseismic and seismic slip, and phenomena such as slow slip, low-frequency earthquakes, and tremor. However, there is still considerable uncertainty about which lithologies and which properties control these processes in subduction zones, in part because the minerals present in subduction zones are both more varied and more challenging to study. This award will upgrade a triaxial rock deformation apparatus donated to Rice University for the purpose of studying the constitutive behavior of rocks present along the subduction plate boundary. The apparatus will be used to measure the constitutive behavior at temperatures that span the seismogenic zone (500 degrees C) and over 8 orders of magnitude in strain rate. These constitutive relations can then be used in models of fault slip along subduction megathrusts to understand how far landward and seaward earthquakes might propagate, which will inform seismic hazards associated with ground shaking and tsunamis, respectively. The project will fund the development of a rock deformation laboratory by an early career PI and the upgraded apparatus will be used by students to conduct their thesis research. Lab members will communicate to the public about this research through a social media account.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.