Progress in the Project for Development of GPS/Acoustic Technique Over the Last 4 Years

GPS/Acoustic (GPS/A) survey is the most promising way to detect crustal deformation in the ocean far from the coast, where a dense onshore GPS network is not available. Monitoring seafloor deformation is crucial to understand the tectonic state in regions of geophysical significance such as subduction zones. We, Tohoku University, together with Nagoya University and Japan Coast Guard have been dedicated to GPS/A survey around the Japanese Islands and developing its instruments for more than a decade. Especially in 2010, a new project for the development of the GPS/A technique commenced, and since 2012 following the Tohoku earthquake, further acceleration of the project has been taken place. Tohoku and Nagoya Universities have been working on this project for 4 years. In the project, Tohoku University worked on several topics, such as realtime/continuous monitoring of crustal deformation using a moored buoy, automatic survey using an Autonomous Surface Vehicle (ASV), which makes the survey as efficient as possible, and constructing a new GPS/acoustic survey network along the Japan Trench and their intensive survey using a chartered ship. In this paper, we summarize the achievements in each of the topics above.