2004 年 50 巻 3 号 p. 209-212
We report that tide gauge records at Maisaka, situated near Lake Hamana in the south coast of Tokai area, show upheaval of the land due to the Tokai slow slip that has started in the fall of 2000. Lowering of the sea level is also seen in the records during the periods of 1980-1982 and 1988-1990. Wethink it is very probable that a slow slip occurred in the period of 1988-1990, because there are some other evidences to support the conjecture: (1) Achange similar to that in recent years was observed by the tiltmeter at Mikkabi on the northwestern shore of Lake Hamana, (2) the spatial pattern of vertical movement in the period of 1988-1990 deduced from leveling measurements was similar to that in recent years, and (3) the seismic activity in the slab near Lake Hamana decreased conspicuously in both periods of 1988-1990 and since 2000. As for the change in the period of 1980-1982, it is possible that it might be caused by a slow slip. However, we cannot say that with confidence for the present because ob servations at that time were not enough compared to the later periods.