EAGER: Quantification of Ocean Water Column Contributions to Bottom Pressure offshore Cascadia using Current and Pressure Recording Inverted Echo Sounders

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Large earthquakes occur at subduction zones where one tectonic plate plunges underneath another. Some of these earthquakes generate large tsunamis. Our ability to understand which earthquakes produce tsunamis is limited by the lack of information about how the seafloor is moving offshore. To address this, continuously recording bottom pressure recorders have been deployed over the subduction zone off the coast of Oregon to estimate long-term vertical deformation. Seafloor pressure measurements combine both seafloor movement and a contribution from the overlying ocean water column. Present efforts to estimate water-column contributions to the measurement use a regional oceanographic model. This model, however, has difficulty estimating pressure variations from eddies and currents near the seafloor, which may be significant. During the project, special instruments will be placed near to the ocean bottom pressure recorders. These instruments will be able to measure the changing pressures from the overlying water column, allowing for a more accurate measure of the tectonic deformation that is occurring offshore. The project supports an early career faculty member from an under-represented group.This project will quantify the water-column contributions to the signal from ocean bottom pressure recorders using in situ observations. Specifically, four Current and Pressure Recording Inverted Echo Sounder (CPIES) will be deployed offshore Oregon near existing ocean bottom pressure recorder benchmarks. CPIES are unique because they simultaneously measure bottom pressure, current, and round-trip acoustic travel time from the sea floor to the sea surface and back. By combining these measurements, the water signal can be separated from the measured bottom pressure signal. These measurements complement existing measurements and provide critical information to distinguish water column signal from tectonic signal for both long-term and transient signals. Methodology developed from previous physical oceanographic process studies will be applied and this effort will demonstrate the application for geophysical studies.