A newly designed surface ship gravity meter named 'NIPRORI' was installed on board the icebreaker 'Fuji' for the 22nd Japanese Antarctic Research Expedition (JARE-22). The icebreaker started from Tokyo, Japan on November 25, 1980, and reached Lützow-Holm Bay of the Antarctica on January 2, 1981. In February, 1981 she left the Antarctica, and returned to Tokyo on April 20. Gravity measurement at sea near the East Antarctica using this gravity meter was successfully conducted, with almost no lack of the measurement throughout the cruise.

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"Bubble memory recording system" for the new model of magnetometer is des cribed.Magnetic bubble memory has several characteristics, e.g., small in size, low power consumption and so on, required for recording system used at the ocean bottom.One board micro computer based on the Z-80A CPU is used for control of the magnetic bubble memory.Every 2.5 minutes' observation of the geomagnetic field at the ocean bottom for more than two months will be possible using the magnetic bubble memory system.

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This is the fourth and fifth reports in the series discussing horizontal crustal move ments in the Kanto and Tokai district, Japan. Some triangulation stations were destroyed or moved during the repeated works and these are checked. The damaged are 9% for the period from 1882/1902 to 1924/1926, 8% for the period from 1882/1902 to 1931, 23% for the period from 1882/1902 to 1973/1980 and 21% for the period from 1924/1926 to 1973/1980. The displacement vectors for the damaged stations are not calculated. The results of calculation for displacement vectors are summarized as follows: 1) The detected displacements are closely associated with the 1923 Kanto earthquake for the period from 1882/1902 to 1924/1926. In the south Kanto district, magnitude of the displacements are as large as 2?`4 meters, and orientation of the vectors is toward the sea, while the displacement vectors in the north part of the Izu peninsula are very small in their magnitudes. 2) In the north part of the Izu peninsula, the displacement vectors for the period from 1882/1902 to 1931 are associated with the 1930 Kita-Izu earthquake, which seems to be the after shock of the 1923 Kanto earthquake. In the south part of the Izu peninsula, orientation of the displacement vectors is toward NNW and magnitude of the vectors are almost 1 meter. The crustal strain in this area was unreleased during the discussed period. 3) The displacement vectors for the periods from 1924/1926 to 1973/1980 and from 1931 to 1973/1980 are not affected by any large earthquake. The displacement vectors are quite reversed in the south Kanto district as compared with the coseismic one. 4) The displacement vectors for the period from 1882/1902 to 1973/1980 are affected by the 1923 Kanto and the 1930 Kita-Izu earthquakes in the Kanto district, while in the Tokai district the displacement vectors show the stationary and accumulated crustal movement which is not affected by large earthquakes. 5) The stationary crustal movement in the Kanto-Tokai district is estimated as a few cm/yr in the rate and NNW in the direction. The horizontal crustal move ment quite depends on the NNW drifting of the Philippine Sea plate.

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The relation between ground-strain changes observed with laser extensometers at the Amagase Observatory and the change of the water level of the Amagase Reservoir existing near the observatory has been investigated. As results, when the water level in the reservoir drops from an elevation of 70 m to an elevation of 60 m, the horizontal and vertical components of laser extensometers installed in normal directions to the axis of the tunnel show remarkable changes of ground-strains, i.e. the extension of about 2×10⁷ and contraction of about 1×10^-7, res pectively. Horizontal components along the axis of the tunnel are not so much affected by the change of the water level. In order to explain these observational results, we consider a seepage model of the ground water in the porous medium : According to the sudden change of the water level of the reservoir, only the normal stress in the direction across the tunnel may be produced in the vicinity of the tunnel and then remarkable changes of ground-strains may be observed across the tunnel.

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Comparisons of spectral characteristics of rates of changes in the Earth's rotation, the rate of the Earth's rotational speed and polar motion, and those of crustal movements in Japan are made. For variations of about one year, the rate of changes of the Earth's rotation is comparable with that of the gravity changes. The rates of changes in strain and tilt, however, show a large value than that of the Earth's rotation. For the spectral band of 1/10-1/100 y, it needs to study spectral characteristics of the rates of changes of the Earth's rotation and those of gravity, strain and tilt in the future.1. Observations of the Earth's rotation, changes of the Earth's rotational speed and polar motion, with new techniques may be affected from crustal movements of the observing sites. Since Japan may be an active region of crustal move ments, it may be of use to study frequency spectra of both the Earth's rotation and crustal movements in Japan [1]. In study of the Earth rotation we often use an expression of the rate of relative changes. This expression, however, is not convenient for vertical crustal deformations, because the definition of the standard scale is not clear. We consider only gravity, strain and tilt in crustal movements. We shall express the rate of rela tive changes in units of radian/year. For a case of a periodic variation the rate of relative changes is expressed by (relative changes of the amplitude)/(period) and it is written as 2π×(the amplitude of a variation/length of a day)/(period) for the Earth's rotational speed especially.

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Formulas for sequential solutions with condi tion equations are constructed in terms of matrices and proved by means of the concept of "fictitious observations."

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This document is the quadrennial report of gravimetric work in Japan during the period from July 1978 to March 1982. Its purpose is to submit to the International Gravity Commission of the International Association of Geodesy at its General Meeting held in Tokyo, Japan, from May 7 to 15, 1982. We summarize gravimetric work such as international and domestic connections of gravity network, absolute and relative measure ments, marine gravimetry, tidal and non-tidal gravity changes, theoretical researches, etc. Complete references of the related articles will be found in the bibliography toward the end of this report. The editor has compiled this report from manuscripts submitted by the International Latitude Observatory of Mizusawa, the Geographical Survey Institute, the Meteorological Research Institute, the National Institute of Polar Research, the Hydrographic Department of Japan, Tohoku University, the Earthquake Research Institute and the Ocean Research Institute of the University of Tokyo, the Tokyo Institute of Technology, Kanazawa University, Nagoya University and Kyoto University.

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