Abstract
The Fujikawa fault that was discovered three years ago is important for the prediction of the apprehended outbreak of the Tokai earthquake. The latest activity of the fault was recorded in 1854at the time of occurrence of the Ansei Tokai earhquake (M=8.4). The Fujikawa fault runs northward from themouth of the Fuji river across the western slope of Mt. Fuji. The southern extension of the Fujikawafault is the Suruga Bay fault that is assumed to run along the Suruga trough. The Suruga Bay-Fujikawa faultsystem is a great left-lateral strike-slip active fault: the Suruga Bay fault shows a left-lateral offset of submarine topography of about 20 kilometers, whereas the Fujikawa fault shows a rapid average velocity of leftlateral displacement of 3.3cm/y. The fault system dislocates the Nankai trough that is regarded as a boundary between the Philippine Sea plate and the Eurasian plate. The surface expression of the Fujikawa fault is very slight because faulting has proceeded simultaneously with the growth of Volcano Fuji and the accumulation of the Fuji River fan-dellta deposits that has been promoted by postglacial rise of sea level. The surface trace of the fault is discernible by analysing abundant storage of water well dataand historical documents in addition to rarely discovered geological and geomorphological evidence.
