Abstract
Discharge rates of many springs in Awaji Island increased markedly just after the 1995 Kobe earthquake. For the following one year, the discharge rates at the six springs had gradually decreased to less than 50% of the rates measured in May 1995. On the other hand, major chemical composition did not change except for one spring located in Nojima-ezaki, the northern end of the island. The change in Nojima-ezaki is a long term fluctuation of anion composition. The concentration of bicarbonate ion decreased gradually, and the concentration of nitrate ion increased simultaneously. In Awaji Island, bicarbonate and nitrate ions characterize deep and shallow groundwaters, respectively. Therefore, the observed geochemical fluctuation is thought to be caused by a change of mixing ratio of groundwaters at different depths.
