[J07-3] Tracking the sea floor in motion III

[J07-3-03] Real-time observation system of pressure gauges and accelerometers on seafloor using ICT through seafloor fiber cable installed in the off-Sanriku region, Japan

^○Masanao Shinohara¹, Tomoaki Yamada¹, Shin'ichi Sakai¹, Hajime Shiobara¹, Toshihiko Kanazawa² (1.Earthquake Research Institute, The University of Tokyo, Tokyo, Japan, 2.National Research Institute for Earth Science and Disaster Prevention, Tsukuba, Japan)

A seafloor cabled system is useful for study of earth science and disaster mitigation, because real-time and long-term observation can be performed. A new system has been required from views of costs and flexibility of measurements. We have been developing a system using Information and Communication Technologies (ICT) for data transmission and system control. The new system has flexibility since software processes various measurements. Reliability of the system is kept by using redundant system which is easily constructed using the ICT. The first system based on this concept was deployed in Japan Sea. Development of the second system started in 2012. The second system has both seismometers and pressure gauges. An observation node has a CPU and FPGA, and the system uses standard TCP/IP protocol with a speed of 1 Gbps for data transmission, system control and monitoring. IEEE-1588 (PTP) is implemented to synchronize a real-time clock, and accuracy is less than 300 ns. We developed two types of observation node. One equips a pressure gauge for observation of tsunami-waves and vertical crustal deformation, and another has an external port for additional sensors using PoE. Deployment of the second system was carried out in September 2015 by using a commercial telecommunication cable ship. At completion of the deployment, the system started collecting data on seafloor immediately. The noise levels at the deployed system are comparable to those at the existing cabled system off Sanriku. Reflecting a low noise environment, many earthquakes were recorded clearly. From the pressure data, pressure measurement has a resolution of less than 1 hPa, which corresponds to a change of water height of less than 1 cm, and all the pressure gauges in the system have collected consistent tidal data. Tsunami-waves in November 2016, which were generated by an earthquake with magnitude of 7.4 off Fukushima were clearly observed by all pressure gauges in the system.