[S-TT42] Applying optic fiber sensing to earth science

[STT42-09] Seismic, geodetic and tsunami monitoring using seafloor cables with optical fiber sensing: Concept and Implementation

*Masanao Shinohara¹, Shin Aoi², Takeshi Akuhara¹, Eiichiro Araki³, Koichiro Obana³, Masataka Kinoshita¹, Takashi Kunugi², Shuichi Kodaira³, Tetsuya Takeda², Takashi Tonegawa³, Masaru Nakano³, Kiwamu Nishida¹, Kimihiro Mochizuki¹, Tomoaki Yamada¹ (1.Earthquake Research Institute, University of Tokyo, 2.National Research Institute for Earth Science and Disaster Resilience, 3.Japan Agency for Marine-Earth Science and Technology)

Keywords:Seafloor seismic, geodetic and tsunami monitoring, seafloor cable observation system, Distributed Acoustic Sensing, optical fiber

Seafloor seismic and tsunami monitoring around Japan has large progress by constructing large-scale seafloor cable observation system (e.g. S-net) and up-to-date plug-in cabled observatory system (e.g. DONET). However we still have marine areas without observation. It is indispensable to cover the whole marine area around Japan for science and disaster mitigation. Recently Optical Fiber Sensing (OFS) technology such as Distributed Acoustic Sensing (DAS) is developed and is available for seismic and geodetic observation. Especially DAS is attractive for seismic observation, because spatially high-density data can be obtained for a long distance. The DAS observations have been carried out using fibers in existing seafloor observation cable systems in Japan, and it is found that the DAS data by seafloor cables are useful for the monitoring. In addition, technical developments are continued to perform geodetic and tsunami observation using the OFS technology. However, difficulties, such as processing method of data and real-time processing of large volume data, have also been recognized. Because modern seafloor cables use optical fibers for data transmission, observation areas can be enlarged using existing seafloor cables. We started discussion for construction of seafloor seismic, geodetic and tsunami monitoring network to cover areas with no marine observation around Japan archipelago using the OFS technology. First we have recognized current status of observations with the OFS technology and analyses of the OFS data. The OFS, especially DAS observation has capability to provide precise hypocenter location, exact determination of magnitude, and focal mechanism in real-time. Detection of tsunami and crustal movement using the OFS technology is though to be possible. We considered performance of DAS observation using existing seafloor tele-communication cable around Japan islands. Although there seems to be problems to solve, for examples, authorization and permission, we found many regions without marine observation can be covered by use of existing seafloor cables. Finally we examined how the OFS data involve the early warning system. In this presentation, we will show the concept of seafloor observation system with the OFS technology in the future and practical implementation of the system.