Chloride (Cl-) and sulfate (SO42-) ion concentrations of ground water
issuing from two wells located near the epicenter of the Kobe earthqua
ke in Japan fluctuated before the disastrous magnitude 7.2 event on 17
January 1995. The samples measured were pumped ground water packed in
bottles and distributed in the domestic market as drinking water from
1993 to April 1995. Analytical results demonstrate that Cl- and SO42-
concentrations increased steadily from August 1994 to just before the
earthquake. Water sampled after the earthquake showed much higher Cl-
and SO42- concentrations. The precursory changes in chemical composit
ion may reflect the preparation stage of a large earthquake.