Monitoring system for submarine earthquakes and deep sea environment

Although more than 80 percent of earthquakes in Japan occur on the seafloor, the seafloor seismic network on the seafloor is sparse and insufficient. To increase the network, the Comprehensive Seafloor Monitoring System was deployed in Nankai Trough off Cape Muroto in March 1997. The prototype system is a combination of observatories with a cable and without a cable. The former system comprises of two seismometers, two tsunami pressure gauges and a seafloor observatory with multiple sensors and 125 km long optical cable. The data are sent in realtime to the land station at Muroto and they are also transmitted to JAMSTEC in Yokosuka and Meteorological Agency of Japan. The latter system, which could be deployed at any place, is comprised of a seafloor observatory with multiple sensors and four long-term digital ocean bottom seismometers. The data could be recovered once every month by releasing pop-up buoys to the surface through the satellite. The system with a cable was deployed on the landward slope of Nankai Trough off Muroto at water depths between 1286 m and 3572 m. The system without cable will be deployed 200 km off Muroto in Shikoku Basin at a depth of 4300 m in early 1998. Five similar systems will be deployed until the year of 2002.