傾斜観測の中期異常の解析と降雨の影響

抄録

Continuous observations of the crustal tilt by use of a water-tube tiltmeter have been recorded in the old Osakayama tunnel of former Tokaido-line since 1965. The effects of monthly precipitation on the monthly changes of the tilt have been calculated. Compensation for these effects has been made in calculating the amount of tilt for each month.
In orderr to detect anomalous changes of the crustal tilt in these observations, first the average values of each monthly tilt were estimated for every overlapping three years periods thus: 1966-1968, 1967-1969, 1968-1970 etc.. Next, the monthly deviations of the observed tilts from the average tilt were calculated. Anomalous tilts larger than monthly mean square errors of the average tilts have been noted.
Large anomalous tilts have been detected for the periods of 1967-1969, 1977-1978 and since 1984. The seismicity around the observatory was very active in the period 1967-1969. A check of anomalies since 1984 performed by comparing the automatic recordings with the visual measurings of the water-tube tiltmeter itself and another water-tube tiltmeter which is installed at deeper place in the tunnel and parallel to the first one. Also, the ambient temperature and the ground water level in the tunnel were measured to estimate their effect on the anomalies.
The schematic models of the anomalous crustal tilt are studied to interpret the mechanisms of this recent anomalous change.