1999 Volume 29 Issue 1 Pages 13-24
In Awaji Island located near the epicenter of the 1995 Kobe earthquake in Japan, a large amount of groundwater discharged along active faults and geological boundaries after the earthquake. On the other hand, water levels of many wells remarkably dropped in highland of the island. The both hydrological phenomena are thought to be caused by increase of permeability in the groundwater aquifer by the earthquake. To prove the hypothesis, we analyzed oxygen and hydrogen isotopic ratios of the anomalously discharged groundwater, and estimated the mean altitude of the recharge area of the groundwater by using altitude effect of hydrogen isotopic ratio. As the results, the estimated mean altitude of the recharge area is clearly different from the altitude of the discharge area, and corresponds to that of the area where water level dropped after the earthquake. The results support the hypothesis that increase of permeability caused the increase of discharge rate of groundwater in the low land and the drop of groundwater level in the highland. However, as to the groundwater along the Higashiura fault, the estimated mean altitude of the recharge area is consistent with that of the discharge area. The reason may be related to the hydrological disturbance effect of the Kusumoto fault to block the groundwater flow.
