Observations of Crustal Movements at Ikuno (1977- 1983)

Abstract

Continuous observations of Crustal movements have been carrying out since 1977 at Ikuno, which is located in the northwestern part of Kinki District, with four horizontal components of extensometer, four components of horizontal pendulum type tiltmeter and water-tube tiltmeters of which four pots are specially arranged to form a quadrate. These special arrangements of observational instruments enable a high-accurate analysis of ground strains and tilts by changing the combination of components used for analysis. Thus reliability of observed values are easily estimated from the com parison of results obtained from different combination of observed components. An attempt to detect the reliable crustal movements is shown in this paper. Secular strains and tilts observed and analyzed by the new methods indicate remar kable changes during the period from the late 1978 to the early 1980 and also in the mid-1981. These changes are characterized by the mode that rotation of axis of principal strains coincides with change in direction of maximum tilt. The patterns of horizontal strains obtained from geodetic survey indicate that Ikuno is situated in the middle of three characteristic block, so it seems that different stress changes in each block alternately affect the crustal movements observed at Ikuno quasi periodically.