1996 Volume 37 Issue 4 Pages 351-358
Data on various hydrological and geochemical fluctuations caused by the 1995 Hyogo-ken Nanbu Earthquake were accumulated. We reported fluctuations of the relatively shallow groundwater at the Nuruyu area, the Northern Awaji Islands, and those of the deeper one at the regional (about 300km×300km) scales. Then, we briefly reviewed the precursory geochemical changes in groundwater.
Groundwater gushed out soon after the earthquake at around the Nuruyu and Nojima-Tokiwa areas, which are situated to the east of the Nojima fault, and then has dried up within the several months. There has been no sign of the recovery of groundwater level in wells one year after the earthquake. The water springing out at the hanging wall side along the Nojima fault seemed to be moved from the eastern mountainous area where groundwater has dried up.
Groundwater in deep underground also fluctuated by the earthquake and their spatial distribution seemed to be related to the distance and the direction from the epicenter of the earthquake. Temperature increase at several hot springs has also been observed after the earthquake.
The investigation of the groundwater fluctuations is important not only for the prediction of earthquakes but also for the engineering geological activities, such as planning water supply for the mountainous villages, monitoring and solving groundwater pollution problems, and evaluating long-term stability of deep underground environments. We proposed several plans to monitor and manage data on groundwater fluctuations both in usual times and at earthquakes. We also showed the recommended countermeasure for the fluctuations of hot springs, and pointed out the importance to prepare water supply plans for the places where the drops of water levels have been observed by the previous earthquakes.