The relation between the seiche in Aburatsubo Bay and the concerning crustal tilt atthe Aburatsubo Observatory has been already reported in the previous paper [1]. Four sets of TEM-tiltmeters [2, 3] measured tilt, while the seiche observation was made by using a pressure type tide-gauge during the period from February to May, 1979. The ratio of tilt and seiche amplitude is empirically determined as a function of the distance from the coast line on the basis of the results of observations. That is T=C exp (-λD), where T is the tilt-Seiche ratio (10^-5 sec. of arc/mm), C=11.7, λ=0.0135 (meter-1) and D is the distance (meter) from the coast line. Although the observed ratios are greater than the theoretical one by factors of 1.2-1.3, the azimuths of maximum tilt agree well at each tilt observation site .

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Using the data of Doppler satellite observations at Kanoya, Dodaira, Mizusawa, and Shintotsugawa, transformation parameters of the Japanese geodetic coordinate system, the translations and rotations with respect to the average terrestrial coordinate system, were obtained. The computations were carried out for four mathematical models by the method of least squares. The results, for example, of Molodensky model, were χ₀=-138.99±2.20 (m), y₀=525.95±2.07 (m), z₀=679.94±2.41 (m), ψ₁=1.20±0.89 (m), ψ₂= -2.67±1.06 (m), ψ₃=-0.13±0.60 (m), k=4.931±4.491 (10^-6).

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We analyzed data obtained by the water-tube tiltmeters and the horizontal pendulum tiltmeters installed at the OGA and NIBETU station of the Akita Geophysical Obser vatory for the period of 1968 to 1975. The distance between the stations is apart about 39 km and we perform a comparative study for ground tilt. Short and long period ground tilt characteristics are clarified using Chebychev approximation funciton. It is shown that ground tilt variation at the OGA is 5 to 10 times greater than that at the NIBETU by the end of 1973 when anomalous strain changes are recorded at many crustal movement observatories in Japan, and after that time ground tilt variation for both the stations becomes almost the same order. It is found that ground variations observed by the horizontal pendulum tiltmeters, the water-tube tiltmeters and the level ling show similar tendency, but the ground variation obtained by horizontal pendulum tiltmeters is about several times larger than that by the water-tube tiltmeters and ground movement obtained by water-tube tiltmeters is larger about one order than that by the levelling. It is also found that the OGA peninsula moves clockwise. It is noted that tilt move ments showed anomalous change before the earthquakes with magnitude 5.3 and 6.2 occurring at the distance 30 km from OGA and 80 km from NIBETU respectively.

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The 1st order triangulation network across the Suruga Bay, Honshu, Japan was surveyed three times in 1883/1891, 1931, 1973 respectively. The earth's horizontal strains were deduced from the survey data for different three periods, 1833/1891-1931, 1931-1973, and 1883/1891-1973. The results of calculations show that the earth's surface is com pressed along almost NW-SE direction throughout the whole period. Compression axis is directed to N46°W and maximum shear strain velocity is 3.6×10^-7/yr in the northern part of the Suruga Bay. These values are N52.5°W and 1.6×10^-7/yr in the middle of the Suruga Bay, N28°W and 3.1×10^-7/yr in the southern Suruga Bay, respectively. The earth's strain that is accumulated during the period from 1854, year of Ansei Tokai earthquake, to the present in the Suruga Bay is estimated by using the obtained strain velocity.

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The effect of rainfalls appeared on the records of tiltmeters and strainmeters at Yura were investigated in relation to the amount of rainfalls. It was found that (1) the peak values in the tilt and strain due to rainfall (per 1 mm of rainfall) showed remarkable temporal changes and the conversion of the trend corresponded fairly to that in the secular tilt and strain observed by the same instruments, (2) the effect of rainfall in the summertime, namely in the wet season was smaller than that in the wintertime, namely in the dry season, and (3) an annual variation appeared on a strain component could be explained as the effect of rainfalls. Especially the good correspondence between the rainfall effect and the secular change means that the tilt and strain response of the ground to rainfall might change according to the crustal stress, probably by the change of the permeability of the underground water.

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