The causes of the excitations of the nearly-diurnal nutation are classified into the two categories. One is due to the perturbing forces acting to the whole earth, including the mantle and the core, from the other independent dynamical system. Another cate gory is due to the interactions between the mantle and the core. The latter causes are inadequate to explain the ratio of the amplitudes between the narly-diurnal nutation and the Chandlerian polar motion, because we are obliged to assume the very short time scale for the electromagnetic disturbances of the liquid core. On the other hand, the causes from former category seem to be sufficient to explain the observed amplitude of the nearly-diurnal nutation, though they have a very poor efficiency.

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Chebychev approximation function is employed for analyzing data observed by extensometers and water-tube tiltmeters. It is revealed that this method is very useful for the analysis of secular variation, because a small number of Chebychev coefficients can produce approximated observation data sufficient for analysis. It is shown that characteristics of secular crustal movement are easily investigated by filtering by the use of adequate Chebychev coefficients. As an example, this method is applied for the data obtained by extensometers and water-tube tiltmeters in Akita Geophysical Observatory.

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The summary of distance measurements of six base-line networks in the western Japan, made with a Geodimeter model 6 since 1968, is presented. Precise measurements of three lines in a tunnel of the Amagase crustal deformation observatory were repeatedly made during 1970-1978. As a result of these measurements, strain accumulations exhibited the rates of (2.6-1.5)×10-6/year for the length of 400-1700 m. And the strain accumulation obtained from continuous records of a super-invar bar extensometer installed at the same turnnel exhibited the rate of 1.9×10-6/year for the length of 40 m. Both results are consistent within the observational error. At the Donzurubo and Wakayama networks, trend of strain accumulations obtained from electro-optical distance measurements are also consistent with those from continuous observations by extensometers.

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The seiche obtained from tide gauge data in the Aburatsubo Tide Station has the period of 13.5-15.5 minutes and the amplitude of 85 mm. In order to confirm the Seiche theoretically, the author applies a Y-shaped one-dimensional model to Aburatsubo and Moroiso bays. The result shows that the free oscillation of sea-surface has the periods of 12.93, 7.18 and 4.82 minutes, respectively, corresponding to the fundamental, the second and the third harmonic waves, although the existence of higher harmonics is not confirmed from the observation. It is proved that the node of the second harmonic is near the tiltmeter station, and Koajiro bay seems ineffective on the seiche in Aburatsubo bay. Tiltmeter observations indicate that the effects of the seiche have E-W and N-S tilt components amounting to 2.35×10-3 and 9.43×10-3 second of arc, respectively. On the other hand, the tilting amplitudes by the seiche are theoretically estimated to be 2.95×10-3 and 3.21×10-3 second of arc, respectively. The calculated result shows a good coincidence with the E-W component observed but it becomes about a third of the observed value for the N-S component.

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Since 1972, the crustal deformation has been observed by use of silica tube exten someters, water-tube and horizontal pendulum tiltmeters at Abuyama Seismological Observatory. The principal axis of compressional strain obtained seismologically and geodesicallylies in approximately E-W direction, but the observation of secular strain in our vault indicates the extension in E-W direction. This contradiction may be explained as follows. The fold with NS axis is advanced by the compresnional force in E-W direction and the hanging wall of fracture zone (N20?KE strike; dip angle of 20?KW) at the local antiform slides down to the west side. Thus, the progress of shear fold results in the extension in E-W direction. Some of instruments are set across a fracture zone about 1 m thick. The thickness of this fracture zone with left lateral slide component is increased by precipitation and decreased by discharge of water. The discharge from observation, vault increased abruptly mid-1975 and 1976. The variations of discharge, strain and tilt are compared with the weekly count of micro-earthquakes, assuming the seismicity may represent the stress change in wider area. But the correlation between them is vague.

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Simultaneous observations of earth tides were carried out by tiltmeters of three types at the Aburatsubo and the Nokogiriyama Crustal Movement Observatories during the period from December 1977 to March 1978 for the purpose of comparing the characteristics of these tiltmeters. The tiltmeters used in these observations were V-M horizontal pendulums, Super-Inver horizontal pendulums and TEM tiltmeters. A third of the observed records was analysed by the Method of International Center of Earth Tides. The preliminary results are compiled in Table II.

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The tidal gravimetrrc observations were carried out by means of three LaCoste and Romberg gravimeters at the Aburatsubo and the Nokogiriyama Observatories during the period of about three months from December 1977 to March 1978. The tidal factors were obtained as 1.24 to 1.42 for the main tidal components, that is O₁, K₁, M₁ and S₁, from the observed data.

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