Four tectonic plates (North America, Eurasia, Pacific, Philippine Sea) meet at the Kanto district, causing complicated seismic activity there. In addition to the Tokai Earthquake (M~8), supposed at the Suruga Trough and the Odawara Earthquake (M~7), supposed at the western part of the Kanagawa Prefecture, it has been pointed out that the Tokyo metropolitan area may suffer from a medium sized earthquake directly underneath in a near future. Crustal strains have been increasing since they were reset to zero in 1923 by the great Kanto earthquake and the earthquake potential is now large enough to cause an earthquake up to M~7 directly under the Tokyo metropolitan area.

The project to monitor regional crustal deformation in the Tokyo metropolitan area by using space geodetic techniques has been started in 1993 by CRL. It is planned that four stations surrounding Tokyo are equipped with both Very Long Baseline Interferometry (VLBI) and Satellite Laser Ranging (SLR) fascilities and daily routine geodetic VLBI/SLR observations are performed in this network to detect precursory crustal movement that may occur pre-seismically. These points also provide positional references for the nationwide network of the Global Positioning System being constructed by the Geogarphical Survey Institute (GSI), Japan.

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Last Update: January 4, 1999