Observations of the rotational strain on the earth tide by means of rotationmeters have been carried out in the Osakayama Tunnel of the former Tokaido Line. Gradients of the earth tidal displacements, aus52°E/a(S38°W) and aus38°w/a(S52°E) have been obtained as
∂u_S52°E/∂(S38°W): M₂-tide=0.25×10^-8 cos (2t-22°),
∂u_S38°W/∂(S52°E): M₂-tide (mean)=0.425×10^-8 cos (2t-3°) .
We have the rotational strain (ω_z) respect to the vertical line are calculated as
ω_z=0.103×10^-8 cos (2t-145°).
It has been discussed followings. 1) The rotational strain respect to the vertical line (ω_z) should be nil on the spheroidal type deformation of the body tide, but should not be nil on the tortional type deformation. 2) The rotational strain (ω_z) caused by the load tide should be also nil around the horizontal sea bottom. But the ω_z should not be nil around the sea bottom with gradient normal to the radius vector respect to the observatory only. 3) According to that the observed S₂-tide was nearly normal, the atmospheric effect was negligible.

抄録全体を表示

Since Dec. 1976, EDM (electro distance measurements) has been repeated at an interval of 1-2 months at the Futagawa base-line network installed in Toyohashi city, central Japan. Directions of base-lines are roughly aligned to the direction of contraction in this region. At Futagawa network, measurements have been conducted as much as possible under good meteorological conditions. The following conclusions are obtained. 1) During the period of 1977-1978, the rate of contraction in the direction of NW-SE at Futagawa network amounts to (0.9-1.3) × 10^-6/year. This rate of contraction is consistent with such data obtained from other base-lines in the Tokai region with the same direction. 2) When the temperature gradient of lower atmosphere is low, the errors of EDM are almost within ±1.0×10^-6. 3) In order to keep the errors within ±1.0×10^-6, the correction for the frequency change of the instruments and the water vapour pressure can not be neglected.

抄録全体を表示

Characteristic tilt and strain changes are often observed at the time of rainf ails by horizontal pendulum tiltmeters and extensometers at the Yura station, Wakayama Prefecture. Large temporal changes have been found on the amount of tilts caused by rainfalls during the period of these 28 years. Remarkable correspondence of the temporal changes to secular ground tilts at Yura and to the occurrence of local shocks in this region suggests that the deformation of the tunnel caused by rainfalls reflects temporal changes in the crustal stress field through the behavior of underground water. In order to investigate such phenomena more precisely, response curves of ground tilts or strains should be estimated from the amount and pattern of rainfalls. A tank model has been applied to simulate the strain response to rainfalls observed at Yura. Preliminary results show that the strain response is successfully simulated by using a model with two tanks and taking the initial loss of rainfalls and the evapo-transpiration into consideration.

抄録全体を表示

The signals from the interior of the earth such as those of crustal deformations due to tectonic movements or those of tidal deformations are distorted by the effects of miscelaneous factors and superimposed with the noises of various sorts prior to the time we can get final observational data. In this paper, factor analysis of these effects are carried out at first, then, each trouble factor is discussed in details in turn and the investigations so far are briefly summarized, although our knowledge about this problem is not yet plenty.(1) Effects of local conditions... There are many varieties in environmental conditions surrounding the vault. The differences in geological, geophysical and topographical properties may cause block movement in some case and may change the amplitudes and/or directions of deformations in other case. Despite it is very fundamental problem, the investigations of this kind are scarce, so for.(2) Effects of vault itself... Signal distortions by cavity effects are seemed to be un-negligible one, though such effects are not actually taken into account in most cases. Secular deformations of the vault are also serious problem in strain or tilt measurement especially in the case of deep borehole sites.(3) Effects of meteorological elements and ground waters... The changes in temperature and atmospheric pressure act, in some case, as main causes of disturbances. In addition, the effect of precipitation is, in many cases, significant and has complex features. Its affection is sometimes very large having a connection with the action of underground waters which seems to affect the ground strain or tilt considerably in direct or indirect manners. It is not rare that the amount of disturbance due to precipitation of 100-200 mm reaches to the value of the order of 10-5. Although the effects of these meteorological factors including underground waters are comparatively well studied by various investigators and several models are proposed to explain observed disturbances, the mechanisms are not yet fully resolved.(4) Oceanographic effects... Oceanic tides alter the amplitudes and phases of earth tidal records. This affection is serious especially at near coast stations, where also suffers the various disturbances due to sea conditions. The effect of ocean tides is fairly well investigated.(5) Effects of instrumentations... Usually, ground movements are transferred to the pedestals at first. But, in most cases, the effects of this pedestal settings are thrown out of considerations. As to construction of instruments, there are very wide varieties in principles, designs, materials and baseline lengths. The comparison of them is desirable to search for better observation system. Such attempts among different type of transducers have been numerously carried out. But it was seldom to compare the system among different principles. As a transducer, mechanical one has been widely used in Japan combining with optical recording devices. This classical method using mechanical magnification has several difficulties such as solid friction, nonlinearity and mechanical drift. On the other hand, by rapid progress of electronics, we can now easily obtain modern electrical transducer which has very stable and highly precise properties. At present, the precision or reliability of instrumentation is considered to reach the values of 10-12-10-11 in short period, 10-10-10-9/ day and 108-107/yr. The maximum absolute precision in secular sense is thought to be about 10-7 being dependent of the accuracy of laser interferometer in extensometer case and the accuracy of manual reading in water tube tiltmeter case. The spectrum of crustal deformation seems to be inversely proportional to frequency over very wide range from 10-2 to 10-12 Hz. From the viewpoint of detectability of modern instrumentation, their amplitude is enough to catch tectonic movements from observed records. Being inspired by this fact, we should study more

抄録全体を表示

Laser Ranging and VLBI (Very Long Baseline Inf erferometer) are the new techniques in astronomy. One of the most important application of them is the distance measurement on the earth. Here, the present situations of the development in their instrumentions will be described and the expected accuracy of measurements will be discussed.

抄録全体を表示