Observation of the Dilatational Strain of the Earth Crust in the Old Osakayama Tunnel for Many Years

Abstract

The observation of the extensions of the crust has been performed in the three orthogonal directions, they are in the vertical, in S 38°W and in S 52°E in the old Osakayama Tunnel since around 1970. Then, the dilatational strain has been obtained by summation of these observed extensions. The secular change of the dilatational strain was much smaller than each extension. But, the annual deviations of the dilatations from the secular average (standard) change are as large as those of each extension. The partial correlation coefficient between the annual deviations and the frequency of the felt earthquake at Kyoto city was fairly large value (-0.438). The forerunning compressions were usually observed in the time of the heavy precipitations which rained after few precipitations. It is interpreted that this forerunning compression is caused by the load of the precipitation and by the water pressure of the saturated water in the shallow part of the ground.