Geochemical and geophysical monitoring of thermal waters in Slovenia in relation to seismic activity

Abstract

Pre-seismic related strains in the Earth's crust are the main cause of the observed geophysical and geochemical anomalies in ground waters preceding an earthquake. Posočje Region, situated along the Soča River, is one of the most seismically active areas of Slovenia. Our measuring stations close to the Posočje Region were installed in the thermal springs at Bled in 1998 and at Zatolmin in 1999. Since the beginning of our survey, radon concentration, electrical conductivity and water temperature have been measured continuously once every hour. In May 2002, the number of geochemical parameters monitored was extended to ionic concentration, pH and Eh, which are analysed once a month. Before seeking a correlation between geochemical and geophysical anomalies with seismic events, the influence of meteorological (atmospheric precipitation, barometric pressure) and hydrological (water table of the Tolminka River) factors on observed anomalies were studied. Results at Zatolmin showed that some radon variation during the period from June to October 2002 may be related to seismic activity and not only to meteorological effects.