Potential contributions of Seafloor Geodesy to understanding slip behavior along the Cascadia Subduction Zone

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The purpose of the study is to determine the optimum placement of seafloor geodetic monuments along the Cascadia Subduction Zone and the frequency and duration of horizontal and vertical seafloor geodetic measurements required to resolve the character of slip along the offshore portion of the thrust fault. Presently, onshore geodesy has determined that the locked region lies almost entirely offshore, however these data lack proximity and poorly resolve details of the stick-slip behavior near the deformation front and the location of the boundary from full stick slip to some component of stable sliding. This one-year project to assimilate existing models of fault geometry, locking behavior along the fault, onshore GPS data, and field-proven precisions of horizontal and vertical seafloor geodesy into an elastic/visco-elastic model. Using this model construction, various placements of seafloor geodetic monuments will be simulated and the resolving power estimated to determine the minimum required array configuration along Cascadia to constrain regional-scale slip behavior on the thrust fault. The project contributes directly to the first two science goals in the GeoPRISMS Science plan on Subduction Cycles and Deformation: What governs the size, location and frequency of great subduction zone earthquakes and how is this related to the spatial and temporal variation of slip behaviors observed along subduction faults? And how does deformation across the subduction plate boundary evolve in space and time, through the seismic cycle and beyond? The broadest impact of this study will be to provide a guide towards using seafloor geodesy to better quantify the earthquake and tsunami risk associated with a large rupture of the thrust fault within the Cascadia subduction zone. Seafloor geodetic measurements could be collected all along the CSZ as a needed constraint to models of megathrust slip that are mostly constrained by the sub-aerial GPS vectors from the Plate Boundary Observatory, a part of Earthscope. Results of this study will help guide this data collection.