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Using Seafloor Geodesy to Constrain Gorda Plate Kinematics and Shallow Megathrust Locking in Southern Cascadia

Uncertainty regarding the kinematics of the Gorda oceanic plate limits our understanding of regional tectonics and our ability to estimate the earthquake and tsunami hazard along the southern Cascadia subduction zone. Here we describe ongoing efforts to constrain plate motions, rates of convergence, and shallow strain accumulation across the southern Cascadia subduction zone using an array of four GNSS-Acoustic sites surveyed since 2022. Three sites are located on the North American plate along the deformation front between 42.2°N and 41°N, and one site is located on the Gorda plate. All sites were surveyed with a GNSS-Acoustic equipped Wave Glider. Three of the four sites have enough data to resolve preliminary velocities, including site GCC1 on the Gorda plate. Comparison of our measured velocity at GCC1 to that estimated based on the MORVEL 2010 plate model shows that the observed GCC1 velocity is ~10 mm/yr slower than expected. We are using finite element modeling to explore implications of this slower than expected Gorda plate velocity for regional tectonics and shallow megathrust locking.

Session: Linking Subduction Zone Processes and Cascading Hazards in Alaska, Cascadia, Chile and Beyond [Poster]

Type: Poster

Room: Exhibit Hall A+B

Date: 4/16/2026

Presentation Time: 08:00 AM (local time)

Presenting Author: Janet Watt

Student Presenter: No

Invited Presentation: 

Poster Number: 136

Additional Authors