A unified method for analysis of short time-series with observational error is proposed in order to make characteristics of the time-series clear. When 32 points are given in a certain time-series, the orthogonal array L32, whose columns correspond to discrete pulses, is used in this analysis method. These pulses are so-called factors in Design of Experiments. We pick up several main basic pulses and sub-basic pulses which are considered as orthogonal basic vectors in Vector Space, and other random pulses are assumed to be error pulses. Analysis of variance (ANOVA) is used in this method, and significant pulses are detected by F test with 5% significant level . We can easily classify any time-series into several types by the result of ANOVA. As an example, mean sea level analysis at Fukaura and Oga is tried by this method, because we are interested in the earth crust movement in relation to the 1983 Central Japan Sea Earthquake. The result shows that the patterns of the real fluctuations of mean sea level are very similar in the both areas, and abnormal upheaval of crust before the earthquake was found as a statistically significant phenomenon .

View full abstract

Up to the present, the Chandlerian Period has been defined as the mean period of the revolution of the pole around its mean position. However, as the motion of the excitation pole does not contain the Chandlerian component, we can determine the length of the Chandlerian Period under the condition that the motion of the excitation pole attains to minimum after elimination of the Chandlerian component. It is calculated as 416 (mean solar) days. It means the period deduced from the angular velocity of the pole around the instantaneous excitation pole, and is to match better those deduced from the theory of the internal constitution of the earth. The calculated results using the recent data of ERP in high precision show that the Chandlerian Period in this sense seems to have a reality.

View full abstract

The method to obtain the maximum tilt and its azimuth for a single sheet of rock on which a single route of levelling survey is established may be applied to a levelling net of closed circuits. Of course, the azimuthal directions of combined line between 2 bench marks for a closed circuit cover far more directions than those for a single route. Accordingly, considerably reliable values of the maximum tilt and its azimuth can be obtained. In connection with the project of earthquake prediction, intervals of repeated levelling surveys tend to be shortened, and quantities of crustal movements are occasionally small. In such cases, reliable contour lines of movements can not be drawn, but secular change of the maximum tilt and its azimuth can be used as the monitor of the movement of the earth's crust.

View full abstract

To enhance earthquake prediction in the Tokai area, tilt measurement by means of a long water-tube tiltmeter has been conducted in Omaezaki, Shizuoka Prefecture ever since 1979. The water-tube of the tiltmeter is approximately 330 meters long and is laid in an E-W direction about 1.5 meters under the ground. An eight year tilt-record indicates two phases in the vertical movement, a long term trend of eastward uplift and a short term trend which is pretty much in agreement with the sea level change at Omaezaki. A precise levelling survey carried out in the vicinity of the tiltmeter, on the other hand, explains an eastward subsidence, which is a reverse tendency in comparison to the tiltmeter readings. It is deduced that the eastward upward movement is caused by an abnormal local subsidence at the western point of the tiltmeter. The corrected record in which the long and short term tilt components are eliminated will be useful in detecting abnormal crustal movement resulting in a destructive earthquake.

View full abstract

The Geographical Survey Institute (GSI) is responsible for the national fundamental survey which has been carried out for the past century as the basis for mapping and engineering works. Main purpose of the fundamental survey is, at present, to get infor mation for the prediction of earthquakes by resurveying control points and to establish control points for the area where large scale mapping or cadastral survey is planned. The geodetic fundamental survey comprises a number of surveys; precise horizontal geodetic survey, levelling and astronomical observation.

View full abstract