Collaborative Research: Constraints on Interseismic Locking near the Trench on the Oregon Segment of the Cascadia Subduction Zone Using Seafloor Geodesy (GNSS-A)

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This project aims to measure the relative movement between the North American and Juan de Fuca tectonic plates across the Cascadia Subduction Zone to help quantify the earthquake and tsunami hazards. The Cascadia Subduction Zone, which is represented by a major fault at the interface of two tectonic plates, is a potential source of large earthquakes and tsunamis. Recent large earthquakes, such as the 2011 Tohoku earthquake, have demonstrated that rupture can extend to surprisingly shallow depths, where large vertical displacements of the seafloor can generate a tsunami. It is important to learn if the situation is similar on the Cascadia Subduction Zone, increasing the hazard from a large tsunami along the US west coast. Determining whether the seafloor in Cascadia moves at the subducting plate rate or is slowed because the fault is locked locally is also important to the scientific understanding of the fault mechanics. The technical challenge is to make these observations on the seafloor, which is both difficult to access and corrosive to instrumentation. Thus, this effort requires specialized techniques for making the necessary observations. This project will support the training of a graduate student and postdoctoral fellow in the use of seafloor geodetic techniques, and the project will further develop the engineering human resources and infrastructure needed to advance seafloor geodesy. The time series of seafloor benchmarks at three existing sites on the accretionary prism of the Cascadia Subduction Zone offshore Oregon will be extended using the GNSS-Acoustic method. These seafloor sites were established in previous years with varying numbers of surveys on each, yielding initial estimates of tectonic plate velocities at three of four sites along the margin. Three new surveys will be performed with a GNSS-Acoustic-equipped Wave Glider during the two-year project. The Wave Glider approach greatly reduces the survey cost compared to that undertaken with a research vessel. In addition to undertaking the geodetic surveys, new algorithms will be explored that improve the data processing, including algorithms designed to mitigate biases from the acoustic velocity structure of the water column and by capitalizing on multi-GNSS data. Finally, the amount of kinematic locking at the trench will be inferred using elastic boundary element models, with the goal to identify if plate locking varies along strike and correlates with structural features in the outer accretionary prism.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.