Crustal Movement Observed at Amagase Observatory

Abstract

The secular variations of ground-strains and -tilts since 1967 obtained from observation carried out by extensometers, tiltmeters and electro-optical distance measurement have been described. The averaged annual rate of strains and tilts are the contraction of order of 10^-6/year for the results from extensometers and electro-optical distance measurements and I''/year for the horizontal pendulum tiltmeters, respectively. For the water-tube tiltmeter the tilt is one order smaller than that of the horizontal pendulum tiltmeter. The trend of secular variations has changed slightly after 1976. The annual variations of the order of 10^-6 for the strains derived from extensometers normal to the tunnel axis appear associated with rainfall.