Fluid distribution around a seismogenic zone along a plate boundary fault imaged and monitored by controlled source electromagnetic sounding

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In FY 2005, we carried out three feasibility studies and tests for long term monitoring of seimogenic zone. A numerical calculation codes for marine controlled source electromagnetic survey was developed. Marine DC resistivity surveys were conducted at two research cruises. Seismic records of aftershocks of the Sumatra great earthquakes were analyzed. These studies are helpful for new development and refinement of cabled long-term ocean bottom electromagnetometers and ocean bottom seismometers. In FY 2006, underwater tests for these ocean bottom instruments were carried out in a small pool. Also, the off-Toyohashi cable, located on the Tokai mega-earthquake zone, was pulled up by using a cable ship and was deployed after attaching a junction unit to the end. In FY 2007, the newly developed ocean bottom instruments were connected to the junction unit at the end of off Toyohashi cable. The JAMSTEC vessels and a ROV were used for the seafloor operations. As a result, a multidisciplinary c … More abled observatory, whose targets are submarine earthquakes, crustal deformation and groundwater flow below the seafloor, was constructed off-Toyohashi, just on the Tokai mega-earthquake zone. Continuous artificial electric signals are sent from the off-Toyohashi cable simultaneously, so that the first ocean bottom monitoring of electrical conductivity variation below the seafloor was started.Before the continuous seafloor monitoring, marine magnetotelluric surveys were carried out off-Toyohashi area to image the crustal electrical conductivity structure around the Tokai mega-earthquake zone. Twelve instruments were deployed and recovered successfully. The obtained data set show us the conductivity structure of subducting Philippine Sea plate.As a result, several papers and presentations were presented through this project, relating to the cabled observatory, marine controlled source electromagnetic survey and electromagnetic phenomena possibly excited by groundwater flow below the seafloor. Less