The results of continuous observation of ground strains and tilts made at the Fujigawa Crustal Movement Observatory for the period from July 1970 to June 1980 are described in the present paper. In this period, an interesting phenomenon was observed at the first half of 1976. That is frequent appearance of pulse like shaped strain or tilt changes which have following characteristics. (1) There are four types in pulse shapes. (2) The width of pulses ranges from several to several tens minutes. Extensometers show always extension and borehole type tiltmeters show only one side tilt. (3) The amplitude of pulses ranges from 1X10-9 to 6X10-8. (4) The amplitude ratios among different components of strain- or tiltmeters are almost constant. (5) Borehole dilatationmeter which was installed at Shizuoka by JMA also frequently records sudden contraction in the same period. But none of them occurs simultaneously or has any delayed correlation with these events. (6) No earthquake occurs at the time of these events and also is seen no particular high seismicity around the station in this period. Although the doubt whether these records come from instrumental causes or not remains, it is possible to interprete these phenomena as creep events on the minor fault within the observation vault or those on the Itoigawa-Shizuoka tectonic line which is one of the famous active fault in Japan and lies at only 2 km apart from the Fujigawa Observatory. Main features of the observed secular strain or tilt changes are as follows. (1) As to the mode of horizontal strain accumulation, EW-contraction is predominant from 1970 to 1973. From then, NS-extension is predominant until 1975, and after some stagnant period, the contraction in NW-SE direction becomes predominant from 1978. (2) As to the mode of tilt accumulation, gradual S-down movement is the basic trend, on which the fluctuations in ENE-WSW direction are added. This direction of fluctuations coincides to the direction to which the observation vault is excavated. (3) The modes of strain and tilt accumulations roughly harmonize with the general trends of the crustal movements in the wide area including this ovservatory. (4) The average strain rates and tilting rates are (0.15-3) X 10^-7/year and (0.3-1.4) X 10^-7/year respectively, which are comparable to those known from the geodetic surveys. (5) The results of spectrum analysis of the ground strains and tilts suggest that the state which we are now watching with continuous observations is a time section of the tectonic movements surrounding this observatory. (6) Annual precipitation at this station is almost constantly 3600 mm/year. But in 1978, this value diminish to 2600 mm/year and correspondingly the changes of horizontal strains were quite calm in this year.

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　糸魚川・静岡構造線北部の仁科三湖周辺において重力探査を行った.測定地域の重力異常は西から東へ約20mgal減少する.特に東径137゜51,附近では重力異常の急激な減少が認められる.この急激な減少は,糸魚川・静岡構造線の両側で基盤岩に垂直方向の変位があり,その結果,基盤岩が構造線を境にして西側が高く東側が低くなっていることを示しているものと思われる.

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To test the reliability of the parameters of a best fitting ellipsoid derived from the astrogeodetic deflections of vertical in Japan new computations are carried out changing the conditions, that is, the type of an observation equation and the number of parameters, using new deflection data at 342 stations in Japan. The result shows that the shape and dimension of a best fitting ellipsoid are very sensitive to these conditions. This may indicate that the data area is too small to determine an optimum best fitting ellipsoid from only the astrogeodic deflections of vertical in Japan.

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Sea gravity data obtained by use of T . S . S . G. in the west Pacific in the years 1963-1980 are compiled and maps of free air and Bouguer gravity anomaly were made. Gravity anomalies in the west Pacific, especially in the east part, are characterized by gravity high at seamount, gravimetric root around seamount, low gravity anomaly at trench, outer gravity high seaward of trench, and mutual interaction between sea amounts and trenches. Gravimetric and seismic results show that two kinds of seamount exist. One can easily subduct at the trench, in which case the seamount is supported by buoyancy of asthenosphere, and the other one cannot subduct easily because the seamount is supported by buoyancy of the crust.

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　日本の測地座標はベッセル楕円体をもとにして計算されているが,東京天文台・堂平観測所での人工衛星レーザ測距の観測を使って,その補正量を求めた,直角座標系ではdX=-153.96±0.83,dY=493.42±1.32,dZ=691.3±2.22メートルであり,これはまたdψ=11″.827,dλ=-10″.894,N=41.5メートルと表わせる.NはIAU1976楕円体からの原点でのジオイドの高さである.

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Geodetic observations were repeated several times in the KANTO-TOKAI district, Japan, during past a hundred years as follows; This is the first one of the papers in which the authors will give the results of unified net-adjustment, displacement vectors and calculated earth's strains in the KANTO- TOKAI district. The results of the net-adjustment for all observations are given in this paper with some discussions on the obtained accuracy that proved to be sufficient to detect crustal movements in the area.

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An absolute gravimetry apparatus of Mizusawa is equipped with an anti-vibrating device in order to cancel the vertical displacements of the horizontal vacuum chamber. The method of anti-vibration is as follows: Signals from a long period vertical component seismometer (natural period is 30 seconds) on a concrete pier are reversed and given to the piezo elements which are attached to the foots of the horizontal vacuum chamber. On the other hand, the residual vibrations are monitored by another vertical component seismometer (natural period is 15 seconds) on the horizontal vacuum chamber. Experiments were achieved to investigate the characteristics of the anti-vibrating device and suitable electric circuits were developed for vibration measurering equipments. In the experiments it was found that the amplitude of vibration of the horizontal vacuum chamber were eliminated to about one-tenth by making use of the anti-vibrating device, but the rosonance of the horizontal vaccum chamber was seen at about 25 Hz. As a result of anti-vibration, high sensitive measurements of the residual vibration of the horizontal vacuum chamber were obtained and its resolution reached about a few nanometers. The precise calibration of seismometer and removal of the resonance of the horizontal vacuum chamber need further extended studies.

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A method is proposed to deduce the earth horizontal strain from repeated observations of directions and distances at some stations with out any net-adjustment. This is an extension of FRANK'S method in which only direction changes are used, while the distance observations are added in the proposed method.

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