Multidisciplinary observations at an expandable sub-marine cabled station off the Hatsushima island, the Sagami bay, Japan

Western part of Sagami Bay is one of the active tectonic areas in Japan. In this area, Teishi Knoll, volcanic scamount, erupted in 1989 and the earthquake swarms occurs repeatedly every few years in the eastern coast of the Izu Peninsula. The real-time deep sea floor observatory was deployed about 7 km off Hatsushima Island, Sagami Bay, at a depth of 1174 m in 1993 to monitor seismic activities, underwater pressure, water temperature and deep currents. The video camera and lights were also mounted in the observatory to monitor the relations among biological activities associated with the tectonic activities. The observation system including submarine electro-optical cable with a length of 8 km was completely renewed in 2000. The several underwater-mateable connectors are installed in the new observatory for additional observation instruments. An ocean bottom electro-magnetic meter(OBEM), precise pressure sensor and ocean bottom gravity meter were installed using ROV Hyper-Dolphin in the cruise of R/V Natsushima from January 9 to 14, 2005. We started to operate them at February 10, 2005 after checking those of data qualities. Observed data have been sent to Yokohama institute, JAMSTEC. Around the Sagami bay, seismic activity is very high. A large earthquake (M5.4) occurred off Izu peninsula at April 21, 2006, and submarine land slide was then generated. Generated mud flow reached to the Hatsushima station, and moved positions of some sensors. The video camera was able to take a movie of mud flow. An OBEM and other sensors also detected some distinctive changes with the mud flow.