|Budget Amount *help
¥1,100,000 (Direct Cost : ¥1,100,000)
Fiscal Year 1990 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1989 : ¥600,000 (Direct Cost : ¥600,000)
It has been pointed out that a destructive earthquake will occur in the near future in the Tokai District, central Japan, by the convergent motion between the Phillippine Sea Plate and the Eurasian Plate. In order to detect precursory crustal movements of the earthquake, a long baseline (365m) water-tube tiltmeter was set in March 1983 at Sagara,which is the central part of the source region of the presumed earthquake. The direction of water-tube is N60^ﾟ W, Which is the direction of the convergent motion of the Philippine Sea Plate.
The results obtained by the tiltmeter had clear seasonal variations, which was affected by rainfall and temperature. The results corrected, showed that the ground was consistently tilting to the northwest at the rate of about 1 nurad/year. This direction is reverse to that of the regional tilting change obtained from the leveling survey.
In order to investigate the details and mechanisms of the reverse change, we carried out leveling surveys and gravity measurements in the area around the tiltmeter site.
The results of the leveling surveys and the gravity measurements show that the northwest tilting observed by the tiltmeter is possibly caused by a local folding, while the regional tilt change is caused by the plate motion.