A tentative correlation between seismic activity and changes in the composition of thermal waters at Vulcano Island, Italy.

On Vulcano Island, Italy, the thermal water in the shallow water well W2 is a mixture of reservoir water and shallow steam-heated groundwater of meteoric origin. In the period 1986-1988, the composition of the W2 water changed just before two sequences of tectonic earthquakes, from the almost pure reservoir component to the almost pure steam-heated meteoric component. After the seismic activity, the W2 water returned to its pre-earthquake reservoir composition. These changes in composition could be explained by the dilatancy-fluid diffusion model. According to this model, the observed variations in W2 water composition could be the consequence of stress build-up prior to the seismic events, and stress reduction afterwards.