Development of Fiber Optic Strain Observatory in Convergent Nankai Trough Seafloor and Verification Tests in Kamioka-Mine

Detection and analysis of seafloor deformation above a subducting plate interface such in the Nankai Trough is a key to understand how large earthquake nucleates in the plate interface. We conceived a seafloor observation system for seafloor deformation which provides seafloor deformation data in realtime by connecting to DONET seafloor cabled observation network. The observation system includes a fiber optic strainmeter as a component of the sensors. We designed the fiber optic strain instrument for the observatory and performed land test in Kamioka tunnel, Gifu, Japan to verify its performance, seafloor installation methods, and method to correct effect of temperature fluctuation in the sensing fiber to measure small strain change.