Monitoring of Crustal Deformation on the Seafloor Around Japan

Institute of industrial science, University of Tokyo and hydrographic and oceanographic department, Japan coast guard have been constructing the geodetic observation network on the seafloor along the ocean trench regions. Sufficient observational results to discuss the system and the observational method have been established as we accumulated the experiences of the observations. Issues and knowledge that we have through the observations should be fed back to the system and further observation for improvement. One of such issues is one inherent in a cylindrical acoustic transducer. Ranging error depending on the positional relationship between the acoustic transducers is caused. We are trying to take measures to this issue by employing new transducer that has different operational principle from the former one and introducing the concept of the phase center of the acoustic transducer to analysis for positioning the seafloor stations. Tank tests were conducted to evaluate the phase response curves of the acoustic transducers and then the acoustic phase centers of the transducers were deduced from these phase response curves. The comparison of the acoustic phase centers of the old and the new transducers should be needed to retain the continuity of the long-term seafloor geodetic observation.