This paper is the progress report concerning with the continuous observation of crustal deformation at Inuyama. The records used for the analysis are of the extenso meter and water tube tiltmeter, the recording periods of which are 20 months and 34 months respectively. The crustal deformation at Inuyama was revealed by the present analytical results. The direction of the principal strain of extension was found to be from N 45°KE to N 80°KE and is nearly concordant with the strike of geologic structure. Further the direction of principal strain of contraction was estimated from N 10?KW to N 45°KW and is concordant with that of the dip of the geologic strata. Maximum shearing stress was obtained as 0.6×10^-6 per year. Maximum dip was mentained at a constant rate of 0.8×10^-6/year, the direction of which was downwards N 40°KW. The strain with short period was found to be different from the general crustal deformation and was infered to be caused by the change in the pressure of water filled in the pore in rocks beneath the ground. The southeastern upheaved region along the Neo valley earthquake fault generated by the Mino-Owari earthquake of 1891 shows a tendency to subside in recovery movement and the strain accumulation was inferred to be going on with the strain rate less than 1×10^-6/year.

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The author estimates the truncation errors in the Stokes formula integration at the Tokyo datum station, using Kaula's [9] spherical coefficients of geopotential. These errors are obtained at every ten degrees of truncation angle. The results indicate that the truncation errors with regard to η=2 and 3 orders of spherical coefficients are not negligible small. The author also suggests that it is difficult to determine the geoid from the locally obiained gravity anomaly in combination with the anomaly measured by satellite orbit analyses.

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The drift correction often comes into question when gravity measurements are made by use of a spiral spring-type gravity meter. In this paper, the drift data of the LaCoste and Romberg gravity meter G 34 of the Earthquake Research Institute, Tokyo University, is discussed. The writer has observed drift once a day for about eight years since this gravity meter was purchased in 1963. The drift data show evidently annual changes, the amplitude of which exceeds 1 mgal. The drift-rate is large in the winter season but small in the summer. The correlation coefficient between the drift-rate and room tem perature is -0.82. On the other hand, the new type LaCoste and Romberg gravity meter G 210 equipped with continuous temperature control mechanism was purchased on September 1969. The drift-rate of G 210 seems relatively small as compared with that of G 34.

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The noise strain associated with precipitation has been eliminated from the strainmeter record of crustal deformation at Inuyama Crustal Movement Observatory. For this purpose we used the record of the N-S strain component which is much affected by the precipitation. It's annual noise strain eq, amounting to 1.0×10^-6 approximately, can be expressed in the formεq=aqi+blogqs, where a, b are the constants, q_i the spring water (amounts of discharged water) from inner part of the observational gallery, and q_s the spring water from the ground surface. The noise strain calculated by the above equation under the known values of a, b, q_i, and q_s has been subtracted from the original strainmeter record. As a consequence, the noise strain could be reduced to the value less than 20 per cent. The accurate measurements of q_i and q_s are necessary for the elimination of the noise strain associated with precipitation.

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It is well known that the tiltometer is one of the useful instrument for observation of the crustal movement. To detect the characteristic crustal movement accompanied by the earth's activity such as the earthquake, widely distributed observation station should be required. It is desirable that the instruments used at these stations satisfy the conditions such as high sensitivity, high stability, adoption of full automatic continuous recording system and easiness of setting and maintenance. Considering those requirements, the authors developed a small new type tiltometer after the principle proposed by one of the authors and named it TEM-Tiltometer (Tsubokawa's ElectroMagnetic Tiltometer). The characteristics of this instrument are the cross suspension pendulum which amplifies the tilting of the ground and the differential transformer as the transducer. It consists chiefly of above mentioned detector on a reset table, a recorder and electronic circuits. The reset table is used for the both purposes of calibration of the sensitivity and of preventing the record to escape from the proper range of recording chart. The authors set these tiltometers at Nokogiriyama Observatory in 1967 and at Akagane Station in 1968 and have carried out the observation of ground tilting. Their maximum sensitivity reached to 0.6"×10^-3/1 mm on recording chart. This report contains the principle and the structure of the TEM-Tiltometer and some examples of observed results.

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In order to detect anomalous geomagnetic changes related with earthquake occurrences, an observation of geomagnetic total intensity has been carried out at the Tottori Micro-Earthquake Observatory by means of a proton precession magnetometer since 1967. Geomagnetic total intensity is gradually decreasing with almost constant rate (22.5γ/year). By the detailed investigation for the rate of its secular variation, it may be suggested that annual change has slightly been recognized in the rate of monthly mean variation of geomagnetic total intensity. Daily mean values are conventionally used to calculate the difference of geomagnetic total intensity between Tottori and the Kakioka Magnetic Observatory, because they are free from an effect of anomalous local phase lag in the geomagnetic Sq variation of total intensity. On the other hand, D8t correction to daily mean values is made by using the Sugiura's D8t indices in order to remove the effect of magnetic storm disturbances. It can be concluded that the difference of daily mean values shows fairly stable constant value through a month, but is gradually decreasing through a year, and that the relative secular variation of Tottori to Kakioka is estimated to be about 1.5γ/year, of which value is seemed to be normal in Japan as compared with values obtained from the first and second order magnetic surveys made by the Geographical Survey Institute.

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A practical method for the elimination of meteorological and oceanographic effects on sea level by corrections for hydrostatic barometric effect, the mean seasonal variation and the regional mean sea level anomaly can be applied to all Japanese coastal regions. The derived reduced sea levels seem to approximately indicate ground level changes. The mean value of the secular variations of sea level at 33 stations for the period of 1951-1965 is -2.7±1.0 mm/year, indicating uplift. Assuming the reduced sea levels to indicate crustal movements, then a regional uniformity of secular crustal movements over the last 15 years becomes apparent; subsidence on the east coasts of Hokkaido and Honshu and uplift in the other parts of Japanese islands. The gradual fluctuations with a period of 2-5 years, clearly demonstrated by the curves of reduced sea levels, are thought to be real and are probably gradual oscillations of the earth's crust. Finally, the possibility of earthquake prediction based on tidal data is discussed. Although since the onset of tidal observations changes during earthquakes are clearly revealed (e.g. Niigata earthquake of 1964), no reliable examples of abnormal changes heralding such events have been found by the present method, although prior authentic historic records of precursory sea level changes exist (Imamura, 1930). Moreover, reexamination of some abnormal changes in mean sea level apparently precursory to large earthquakes such as the great Kwanto earthquake of 1923 shows that it is more reasonable to interpret such anomalies as mere changes caused by ocean currents rather than by real crustal movements. For practical prediction of earthquakes, the pre sent tidal network in Japan seems still to be of insufficient density for detection of abnormal crustal movements. The author strongly recomends extreme caution in the analysis of precursory events in order to gather completely reliable instaces so that the character of precursory deformation may be studied without the presence of doubtful cases hindering this research.

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