Seafloor Crustal Deformation Observations Utilizing Unmanned Surface Vehicles for Monitoring Fault Locking and Sliding Processes at Subduction Zone Plate Boundaries

While positioning on the seafloor is difficult by means of the global navigation satellite system (GNSS), GNSS-Acoustic (GNSS-A) technique is a powerful tool to detect the seafloor crustal deformation associated with mega-thrust earthquakes that occur in the plate subduction zones. We have been using an unmanned surface vehicle (USV), Wave Glider, as a sea surface platform to perform GNSS-A observations since 2019 and detected the post-seismic deformation of the 2011 Tohoku-oki earthquake along the Japan Trench. Based on the knowledge obtained from the months-long observation campaigns conducted since 2020, the performance required of USVs to perform GNSS-A observations and future prospects are summarized.