上宝における地殻変動の連続観測

抄録

Crustal movements have been routinely observed since 1966 at Kamitakara, which is located in the seismically active northwestern Chubu region, with three sets of quartztube strainmeters, two sets of water-tube tiltmeters and several sets of horizontal pendulum tiltmeters. The observed secular strains indicate remarkable variations during the period from late 1968 to early 1970, and also from mid-1974 to late 1975. These patterns seem consistent but sometimes in reverse sense with the strain changes at other two sites in the Chubu region, Tsukechi and Inuyama. The changes in the strain direction commonly observed at the three sites around the end of 1968 and those consistently identified in the tilt direction at Kamitakara and Inuyama, might be associated with pre-seismic movements to the central Gif u earthquake of 1969. It is also found that the strain and tilt rates at the above two sites change their direction after the earthquake, suggesting partial release of the accumulated strains there. The strain changes in 19741975, on the other hand, appear to reflect more widely-spaced crustal movements . Observations of the earth tidal strains show a gentle increase of tidal amplitude prior to the 1969 earthquake and decrease after the earthquake. More detailed discussion on the earth tidal observations will be made in a separate paper .