New Seafloor Mapping on the Cascadia Margin

High-resolution (~25-m) multibeam echosounder data is critical for understanding seafloor geology and habitats, especially as they relate to offshore earthquake and landslide hazard assessment, sediment dispersal patterns, and resource management. Swath bathymetry data collected by the USGS and NOAA in August 2019 will provide important new information regarding seafloor morphology along the Cascadia Subduction Zone offshore of Northern California and Oregon, including insight into spatial variations in megathrust behavior, upper plate structure, fault segmentation patterns, stress/strain accommodation, and variations in coastal uplift/subsidence. Seafloor mapped using a Kongsberg EM710 multibeam sonar aboard the NOAA Ship Fairweatherwill include more than 5000 km², with areas encompassing a range of seafloor morphologies from the outer shelf to the lower slope in 200-1600 m water depth. These new datasets will be gridded at a minimum 20-m pixel resolution and integrated with existing bathymetry data to provide nearly complete seafloor coverage of the outer continental shelf and slope morphology along the entire U.S. portion of the Cascadia subduction zone. Seafloor and water column backscatter data will also be acquired; these data will be useful for a range of geologic investigations, including benthic habitat mapping, deep coral studies, seafloor seep identification, and evaluating potential sites for offshore renewable energy development. The seabed in this area is composed of a combination of rocky outcrops, uplifted fault blocks, sediment-filled basins, gullied slopes, deep-sea canyons, submarine landslides, and hemipelagic drape. This effort is a continuation of Cascadia research conducted in cooperation with the EXPRESS (Expanding Pacific Research and Explorations of Submerged Systems) framework, which includes partners from USGS, BOEM, and NOAA, as well as other academic, NGO, private sector, and government colleagues.