1981 年 27 巻 1 号 p. 1-10
Secular ground tilts observed at Kishu Mine in Kui Peninsula, Japan from 1952 to 1979 can be represented as exponential functions with a relaxation time of 5.1 years. Assuming the stress-relaxation in a Maxwell body of μ=3×1011, we get the viscosity η=5× 1019 poise. Stress-relaxation in the rock around the tiltmeters is considered the origin of the secular tilts, though stress-relaxation in the metal consisting of the tiltmeters and/or in the concrete base on which the tiltmeters are installed cannot be excluded. No forerunning changes can be found on the secular tilts in periodic ranges longer than 10 days associated with two remarkable earthquakes occurred in Kui Peninsula on Nov. 25, 1973 (Δ=50 km, H=60 km, M=5.9, 5.8). A preliminary analysis of earth tides shows that both the M2 and O1 tilt tides observed at Kishu are well explained as the sum of the solid tides and the oceanic loading effect.