Abstract
To enhance earthquake prediction in the Tokai area, tilt measurement by means of a long water-tube tiltmeter has been conducted in Omaezaki, Shizuoka Prefecture ever since 1979. The water-tube of the tiltmeter is approximately 330 meters long and is laid in an E-W direction about 1.5 meters under the ground. An eight year tilt-record indicates two phases in the vertical movement, a long term trend of eastward uplift and a short term trend which is pretty much in agreement with the sea level change at Omaezaki. A precise levelling survey carried out in the vicinity of the tiltmeter, on the other hand, explains an eastward subsidence, which is a reverse tendency in comparison to the tiltmeter readings. It is deduced that the eastward upward movement is caused by an abnormal local subsidence at the western point of the tiltmeter. The corrected record in which the long and short term tilt components are eliminated will be useful in detecting abnormal crustal movement resulting in a destructive earthquake.
