Monitoring system for submarine earthquakes and deep sea environment

Abstract

Although more than 80 percent of earthquakes in Japan occur on the seafloor, seismic network on the seafloor is quite few and insufficient. As a step to increase seafloor seismic network, 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, 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, comprises of seafloor observatory with imultiple 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 land ward 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.

Simulation of distant tsunami propagation with a radial loading deformation effect

“…The giant tsunamis generated by the 2011 Tohoku and the 2010 Chilean earthquakes were recorded by basinwide OBP gauges operated by the Deep-Ocean Assessment and Reporting of Tsunamis (DART) system (González et al, 1998), and by the seafloor cable system of the Japan Agency for Marine-Earth Science and Technology (JAM-STEC) (Momma et al, 1997;Hirata et al, 2002). The data shown in Fig.…”

Temperature correction and usefulness of ocean bottom pressure data from cabled seafloor observatories around Japan for analyses of tsunamis, ocean tides, and low-frequency geophysical phenomena

“…1). The OBTMs are located at offshore Kamaishi: TM1 and TM2 (Kanazawa and Hasegawa, 1997); Cape Muroto: MPG1 and MPG2 (Momma et al, 1997); and Kushiro: KPG1 and KPG2 (Hirata et al, 2002). OBTM records during periods of more than ten years are used to investigate long-term changes.…”

Compound fault rupture during the 2004 off the Kii Peninsula earthquake (M 7.4) inferred from highly resolved coseismic sea-surface deformation

“…Therefore, the earthquake was assumed to be an intraplate event. This earthquake also caused a moderate tsunami, which was observed by tide gauges along the southern coast of Japan and by three offshore tsunami gauges off Cape Muroto, a GPS tsunami gauge (hereafter, GPS-TG; Kato et al, 2000), and two cabled ocean-bottom pressure gauges (hereafter, PG1 and PG2; Monma et al, 1997;Matsumoto and Mikada, 2005).…”