Compositional variations of gas species occluded in fracture zones (type I) within active faults are essentially the same as those in bubble gases (type II) separating from mineral springs along faults. The variation in type II is hydrogeochemically interpreted as a result of dissolving and degassing of atmospheric air in ground water at various temperatures. The comparison of these variations in both types of gases suggests that Ne, Ar, and N2 in the type I gases are of atmospheric origin and their fluctuation is strongly controlled by the circulation of groundwater, which recharges and discharges atmospheric air at various temperatures. Further hydrogeochemical evaluation shows that a part of He observed in fault zones is of radiogenic origin but its proportion is very small in active faults. In these zones, juvenile He emission related to the tectonic stresses causing earthquake may be substantially modified by the compositional fluctuation of gases controlled by the water circulation within the fault system. Accordingly, monitoring of rare gases except for H2 from historically active faults may be less effective for earthquake prediction. In contrast, gas bubbles of high He content issuing from mineral springs which usually occur along prehistorically active faults are less contaminated by air and may provide some general precursory information concerning regional stresses at depth prior to an earthquake. ¿ American Geophysical Union 1987