GPS/acoustic seafloor geodetic observation - Major results and new approaches

Three research groups, the Japan Coast Guard (JCG) and the Institute of Industrial Science, University of Tokyo,: Tohoku University, and Nagoya University, have been developing precise seafloor positioning systems using the GPS/Acoustic combination technique and carrying out observations along the major trenches in the Pacific Ocean, such as the Japan Trench and the Nankai Trough. The primary purpose of seafloor geodetic observation is to detect and monitor crustal deformation taused by subduction of oceanic plates near the plate boundaries where huge earthquakes repeatedly occur. We have succeeded in detecting interseismic crustal movements and co-seismic displacements with centimeter resolution from multiple campaign observations. However, there still remain some issues in technical and operational aspects. Further efforts are necessary to achieve more precise and stable results.