Chemical characteristics of the Matsushiro spring waters

Abstract

An inspection of the chemical composition of spring waters in Matsushiro, Nagano Prefecture, revealed that the Na/Mg ratio is closely related to the geographical locations of the springs. Two types of waters can be distinguished: one is magnesium-rich waters from the springs in the southeastern area, and the other, sodium-rich waters from the springs in the northwestern area of Matsushiro. The Ichiyo-kan spring, located at the boundary of the two areas, changed drastically the Na/Mg ratio before and after the swarm earthquakes, thus suggesting that the ratio can be used as an indicater of seismic activity in the area. The origin of the two types of the waters is also briefly discussed.