Comprehensive deep seafloor monitoring system in JAMSTEC

Every year more than 80% of earthquakes around Japan occur on the seafloor by plate subduction. As a step to increase the seafloor seismic network, a comprehensive seafloor monitoring system was developed by JAMSTEC. The system consists of: a cable linked real-time seafloor observatory (RTSO), and a mobile seafloor observatory. The former system was deployed in Nankai Trough off Cape Muroto and started the observation in March 1997. The RTSO consists of two ocean bottom seismometers, two Tsunami pressure gauges, a cable end station equipped with multi-sensors and a 125 km long optical submarine cable. The monitored and measured data are sent in real-time to the land station at Muroto and they are also transmitted to JAMSTEC in Yokosuka and the Meteorological Agency of Japan. The ocean bottom seismometers, Tsunami pressure gauges and cable end-station of RTSO was laid on the land ward slope of Nankai Trough off Muroto at water depths up to 3572 m. Five similar systems in total are planned to be deployed around Japan.