This paper is the fourth report concerning the continuous observation of Crustal deformation at the Inuyama Crustal Movement Observatory since 1967. Records of tilt observed with water tube tiltmeters have been analyzed. Observational errors are eli-minated by a suitable high cut digital filter. Short period variation in tilting that amounts to 10
-8 or 10
-7 radian is mainly related to the change of discharged water from the observational vault. Vertical movement at Inuyama has been revealed by analyzing the secular change that is separated from annual one by a simple method reported in the former report. Tilting rate of maximum dip changed greatly, at a nearly constant rate, from 0.89×10
-6 rad/year to 0.16×10
-6 rad/year early in 1970, but the direction of maximum dip stayed about N40°W which coincides with that of minor principal strain. This tilting rate and direction of maximum dip is almost concordant with geodetic data around the observatory. We can find the same tendency in the Quarternary vertical movement, so it is considered that not only horizontal strain but also present vertical movement is in the progressive stage, developing the Quarternary tectonic movement in and around the Nobi Plain. Some problems relating to earthquake occurrence were examined. A phenomenon which might be related to earthquake occurrence was detected for the frequency com-ponents of tilt and strain having periods longer than one year. From about one year before the occurrence of the earthquake (M=6.6) in the central part of Gif u Prefecture on 9th September 1969, all the secular variations of tilt rates and strain rates began to change simultaneously. Again, they changed rapidly in the opposite sense about one or two months before the occurrence of the earthquake. This pattern of change in tilt rates and strain rates may be compared with the three stages of Crustal movement (α·β·γ) before and after the occurrence of major earthquake. Relating to this pheno-menon, problems concerning digital filter technique and meteorological effects have been examined, but there was no negative feature to obscure the possibility mentioned above.
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