A portable laser extensometer system was developed for precise measurements of shallow ground-strains. The system is able to detect two axial strains simultaneously. The resolving power of the system is 2 × 10^-9/digit. The preliminary observation using the system has been carried on since March, 1985, at shallow trenches in Uji campus of Kyoto university. The stability of instruments for mechanical vibrations was examined by a loading test with a motercar straddling over extensometers. Accompanying the pumping of groundwater at three wells existing in the campus, strain changes of the order of 10^-7 were observed. Strain changes caused by meteoro logical perturbations were an order of 10.6 at the most.

View full abstract

The quantity of water vapor in the lower troposphere is an essential factor which controls the accuracy of precise surveying by the NAVSTAR GPS. We have investigated the time changes in the excess path delay by water vapor using data obtained from the routine radio zonde observations by JMA at Wajima, Yonago and Shionomisaki in Kinki District. It is concluded that the effect due to water vapor may be reduced within a range of 2-3 cm, without concurrent observation with a water vapor radiometer, by averaging results from a few days observations in winter, especially in February, under such a weather condition as low temperature and humidity on the ground surface.

View full abstract

A method of free networks adjustment by using orthogonal array, which is called TAGUCHI's orthogonal array in Japan, is proposed in this paper. This adjustment is based on so-called Design of Experiments. Generally observed land subsidence or upheaval are contaminated by leveling error, therefore analysis of variance (ANOVA) for leveling data should be applied in order to measure the observed value by its error. In this paper F test is used, and true difference between old data and new data for land subsidence or upheaval can be tested by F value assuming that significant level is 5%. Basic vectors in the Vector Space for each parameter are intersected orthogonally each other, i.e. It is evident that the observed vector is decomposed by orthographic projection. Then covariance among those unknown parameters are all zeroes, therefore it is intended for practical use.

View full abstract

It is generally difficult to know features of a certain short time-series, because each data has measuring error. In this paper, simple and unified method for analysis of short time-series by using ANOVA (analysis of variance) is proposed. We use 4 basic pulses as cause factors in the time-series. L₈ orthogonal array is used in this method, therefore basic vectors for each basic pulse are intersected orthogonally each other. We can easily classify time-series into several types by the result of ANOVA.

View full abstract

The Miura peninsula shows the anomalous vertical movement when there occurs a large earthquake along Japan trench or Sagami trough. To explain this phenomena, one of the authors (Fujita) proposed the following hypothesis. Under Kanto area, there is a weak zone which contains the fault plane of 1923 Kanto earthquake (let us name the plane as ‘C plane’), The C plane is sensitive to the change of areal strain and some part of the plane creeps when there occurs a large earthquake along Japan trench or Sagami trough. The strike of C plane coincides with the axis of Sagami trough and the dip is 30° in the landward side of the trough. The direction of creep is equal to that of the fault movement in the 1923 Kanto earthquake, SE20°. Therefore, the anomalous vertical movement in Miura peninsula is considered to be a good indicator for forth-coming large earthquake along Japan trench or Sagami trough. In this paper, the followings are deduced applying the hypothesis to the interpretation of the vertical movement in South Kanto area. 1) The general features in vertical movement in the South Kanto is considered to be the combination of subsidence of southern tips of both Boso and Miura peninsulas, uplift in the central part of Boso peninsula, occasional uplift in the southern part of both peninsulas and so on (Figures 1 and 3). 2) The 1968 event can be explained as follows. About 4 years before the 1968 Tokachioki earthquake, the creep started at south-eastern part of the C plane. The displacement reached about 30 cm. After the earthquake, the creeping area diffused into the sorrounding part of the C plane. The displacement reached 15-20 cm in about 3 years (Figures 4, 5 and 6). 3) The anomalous tilt of Miura peninsula, which appears 3-4 years before a large earthquake occurs along Japan trench or Sagami trough and lasts till 3-4 years after the earthquake (Fig. 6), can be explained by the mechanism similar to that mentioned in 2).

View full abstract

Vertical crustal movement contour maps over Japan except Hokkaido are compiled using the fouth (1962-1968), fifth (1968-1975), and sixth (1975-1981) leveling . In order to avoid systematic leveling error accumulation, heights of nine tidal stations are given in the adjustment computation with an assumption that the shape of annual mean sealevel along the coast of the Japan Sea is stable. As a result, vertical movements relative to Wajima tidal station are obtained . The main features of the vertical crustal movements are as follows:(1) Most areas of Japan tend to subside.(2) Rapid and consistent subsidence is found in the eastern half of the Tohoku region, (3) Rapid subsidence for the period between the fourth and fifth leveling turned into rapid uplift for the next period between the fifth and sixth leveling in Pacific coasts of Kanto, Chubu, Kinki, and Kyushu regions.(4) Rapid and continuous uplift is found in western part of Shikoku.(5) Crustal movements mentioned in (3) and (4) do not always agree with those deduced by Kato from mean sea level changes,

View full abstract

A simple conversion method from geoid to gravity anomalies has been developed to obtain the gravity distribution from the satellite altimetric sea surface topography. Spherical harmonic coefficients of geopotential model were used for the components of wavelengths longer than 600 miles (degree 0-36), and as for the components of wavelengths shorter than that, Fourier transform was applied to the geoid data projected onto a tangential plane on the spherical earth. The accuracy of gravity anomalies thus obtained for the wavelengths not shorter than 20 nautical miles is considered better than 10 mgal in case where the satellite track is sufficiently dense to obtain 10 nm x 10 nm grid data of altimetry.

View full abstract