Precise gravity measurement was carried out repeatedly at both sets of the stations, where gravity difference from the base station (Gravity Station of Geophysical Institute of Kyoto University, 979. 72158 gal) is smaller than 1 mgal and where gravity value is almost equal to 979.700 gal, by means of 3 LaCoste & Romberg gravimeters (model G). The obtained accuracy was estimated to be about ±0.015 mgal. The gravity values obtained through the present measurement will give basic data for the future study on time change of gravity in the Kinki District.

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From the view point of earthquake prediction, the preseinmic movements related to the San Fernando Earthquake has been investigated, using the data of geodetic triangulation repeated in the area of the earthquake. A significant accumulation of tectonic strain before the earthquake has been detected from the analysis of retriangulation data. The axes of the maximum compression are in the direction of N-S, and the strain velocity is the order of 3-5⋅ 10^-7/year. This is harmonious to the faulting mechsaism of the earthquake. Records of some strain meters just before the earthquake have been also examined.

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In general, given the error of representation or the error of interpolation, the sufficient and economic distribution of gravity observations for a prescribed accuracy for astrogravimetric leveling or the interpolation of the deflection of the vertical can be' determined. This report discusses in what way and with what accuracy detailed surveys of the form of the quasigeoid and of the deflection of the vertical should be obtained. The folllowing conclusions were obtained. 1. It is advisable to use the indirect method of interpolation of the freeair anomalies, , which makes use of the fact that Bouguer anomalies are in general far less correlated with elevation than free-air anomalies (our system of computing astrogravimetric leveling applies this method). 2. The error of representation and the error of interpolation in north Kanto aree three or four times larger than those obtained by the Russian geodetists on the basis of the dence gravity-station nets of the U.S.S.R. 3. In general, these errors will depend not only on the size of the variations of the gravity anomalies but also on its irregularities. Thus the coefficient k of the righthand side of the empirical formula of the form (1), or (2), which expresses the error of representation or the error of interpolation, should be considered not to be constant but to be variable. Before the astrogravimetric leveling is carried out, therefore, we must have a guarantee that some local gravity surveys already exist, from which the value of k can be determined. 4. On the basis of the error of representation in north Kanto, which may represent eastern Japan approximately, in order to obtain the results of astrogravimetric leveling with an accuracy of ±0"6.21, it is necessary, say, that a regional gravity survey with a density of 1 point per 60 km² exists out to 41 from the middle point between astronomical stations and that the neighborhood of the astronomical station is covered by a gravity station net-1 point per 5-10, km2 in a circle of 8 km radius. Further if gravity observations at an average distance of 7 km for lowlands and mountains, and of 3-4 km for high mountains can be get, the deflections of the vertical with an accuracy of 1" will be obtained. 5. If studied area has a rather smooth gravity-anomaly field, as is true in western Japan, the necessary deflections of the vertical can be adequately obtained on the basis of a rather widely spaced gravity-station net.

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According to the dilatancy model of earthquake occurrence, a possible decrease of elastic moduli, especially of A, in earthquake source regions is expected before earthquakes. A possibility for detecting the change of the crustal property by continuous observations of earth tides are examined. The results indicate that such changes may be effectively detected by extensometrrc observations under some suitable circumstances.

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In gravity measurements, it is naturally presumed that the gravity values obtained are disturbed by certain effects. A thorough investigation for those effects is an essential problem on gravity measurements. Experiments for investigating the following two kinds of characteristics of 9 LaCoste & Romberg gravimeters (G-29, 31, 34, 113, 124, 196, 210, 304 and 305) were cooperatively carried out at Mizusawa inFebruary 1974. (1) Calibration on scale factor of the gravimeters along the route between Mizusawa and Hachinohe (gravity difference 213.1 mgal). (2) Effect due to change of the outer temperature. The following conclusions were obtained through the present experiments. (1) Discrepancy among the scale factors of the 9 LaCoste & Romberg gravimeters was found to be about 2×10-4. Its amount was the same order as for the previous experiments. (2) Effect due to change of the outer temperature is different at each gravimeter. Generally speaking, reading value of the gravimeter increases at when the outer temperature decreases, and there are some phase lags between change of the outer temperature and response of the gravimeter's reading value. In field gravity measurements, it is, therefore, avoidable from effect due to change of the outer temperature in case when the gravity measurement was carried out within 10 minutes just after the gravimeter was taken out of its case.

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At Mikawa Crustal Movement Observatory, the newly designed I.C, amplifier and the quadrature oscilator for the strain- and the tilt-meter are used since January, 1973. From the result of observation, it is found that the out-put of the I.C, circuit is of high stability and of low noise. The out-put of the strain-meter is used as strain seismogram.

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