Radon Concentration in Thermal Water as an Indicator of Seismic Activity

Radon concentration in thermal springs at Hotavlje and Bled has been measured from October 2005 to June 2008 and from October 2005 to September 2007, respectively. At both locations several anomalies in radon concentration were observed, that might have been caused by seismic events. In this study all earthquakes with ratio (D/R) between strain radius (D) and distance to the epicenter (R) greater than 0.5 were taken into account. Five earthquakes occurred in the vicinity of Bled in this period, the strongest at a distance of 17 km with the magnitude M-L=3.8 and four radon anomalies were observed. At Hotavlje fourteen earthquakes occurred in the vicinity with D/R ratio from 0.5 to 2.9. During this period three radon anomalies were observed.