Abstract
Changes in gas concentration (Rn, He, Ar, CO2, CH4, H2, N2, O2) in soil gases along active faults in relation to earthquakes were reported in the literature worldwide. Also changes in gas concentrations from thermal springs and dissolved ions in thermal water were studied in some countries. This research was carried out in thermal springs for the following reasons: because they are representative of deep water circulation, because free gases in thermal water are less contaminated with atmospheric air, and because they are much less influenced by meteorological parameters in comparison to soil gas. We will present the results of radon concentration changes in thermal springs of Slovenia and ground water of Japan.