Runaway Slip: Understanding Nucleation of Subduction Megathrust Earthquakes and Slow Slip Precursors

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Subduction zone earthquakes where 'runaway slip' allows faulting to rupture from depth all the way up to the seafloor can cause enormous tsunamis that devastate coastal population centers. Not all subduction zone earthquakes develop runaway slip- details of a particular fault's frictional behavior dictate what happens. This study will conduct laboratory experiments to determine how different types of fault rock respond to applied forces. Results could improve understanding of whether some subduction zones are more, or less, likely to generate megathrust earthquakes.Current understanding of the mechanical response to shear stress of fault rock is limited by the lack of measurements on relevant natural samples at in-situ conditions. Laboratory shear measurements will document friction at in-situ pressures and temperatures using natural fault zone material. A transition in clay structure is thought to play an important role, along with mineral fabric and pore fluid pressure. A series of experiments on both crushed samples and intact wafers will be conducted. Start and end microstuctural and geochemical analyses will quantify the shearing impacts. Interpretation will focus on the nucleation phase of megathrust earthquakes. A female postdoctoral scientist will lead the study and the results will contribute to advancing knowledge within the GeoPRISMS program initiative 'Subduction Cycling and Deformation'.