CONTEMPORARY VERTICAL CRUSTAL MOVEMENT IN THE TOKAI DISTRICT AND ITS NEIGHBORHOOD, CENTRAL JAPAN

The leveling data of the network covering the Tokai district and its neighborhood, central Japan, are analyzed in order to study the vertical crustal movement in this area. Analysis is performed on the leveling data obtained during 1965 to 1985, together with the sea level data at the tidal stations along the coast within the network. In the least square adjustment of the leveling network, a new velocity model in which time change of crustal movement is taken into consideration was adopted. A comparison between the results of leveling data and of tidal data shows that the mode of vertical crustal movement at the tidal stations deduced from sea level data coincides well with that from leveling data. Based on both of them, the contour maps of vertical rate of crustal movement in the discussed area are charted for three periods: 1965-1974, 1971-1981, and 1979-1985. These maps give us a whole view of the contemporary vertical crustal movements in and around the Tokai district. The main conclusions are summarized as follows: 1) The Akaishi Mountain area and the Omaezaki area have a pattern of reverse movement, that is, Akaishi uplift corresponds to Omaezaki subsidence. This paired reverse movement seems to be a reflection of the subduction process of the Philippine Sea plate along the Suruga trough. 2) Omiya. Kofu, and the Miura Peninsula had been subsiding throughout the three periods. Especially during 1979 to 1985, the place near Omiya subsided at a rate of about - 30 mm/a. The subsidences in Omiya and Kofu are considered to be man-induced ground subsidences. The steady subsidence at the Miura Peninsula can be interpreted as the result of the drag effect of the subducting Philippine Sea plate along the Sagami trough. 3) The movement at Nagoya is one of the most interesting cases. It was in a rapid subsiding state during the first period. Then the subsidence weakened, and turned to be quick uplifting during the third period. This will be also associated with unstable subduction of the Philippine Sea plate, though further study is required to interpret this abnormal phenomenon.