抄録
Immediately after the 1984 Yamasaki fault earthquake of M=5.6, remarkable postseismic deformation, represented by an exponential function, was observed at Ikuno in the northwestern part of the Kinki district, southwest Japan. The exceptional amounts of both strain and tilt changes suggest that the local conditions of the observation site played an important role in disarranging and amplifying local strain fields. The postseismic deformation at Ikuno can be explained as an elastic deformation caused by a large pressure decrease at a disturbing source with a thrust-type pressure distribution. It can be thought of as a characteristic phenomenon occurring under the peculiar conditions in which the observations have been carried out at a closed mine that has now been fully filled up with underground water to a depth of about 1, 000 m. The disturbing source was probably caused by the diffusion of underground water, which has a high hydraulic pressure due to the high water-level in the mine. We think that the movements of underground water sometimes have an important effect on the local ground deformation in the period immediately after an earthquake.
