Radon groundwater anomalies related to the Umbria-Marche, September 26, 1997, earthquakes

Abstract

From May 1996, measurements of the radon content in groundwater and other parameters (pH, electrical conductivity, pressure of dissolved gases and groundwater temperature) were conducted at the Gran Sasso underground laboratory of the National Institute for Nuclear Physics, Italy, using multiparametric equipment. We have analyzed the correlations between radon variations and the stress-strain processes in the rock, and the radon diffusion processes related to groundwater geochemistry. Time series analysis showed strong anomalies in pH, radon concentrations and pressure of dissolved gases, which highly correlate with the Umbria-Marche seismic sequence of 1997-1998. This may be caused by a transient compression phase producing a change of carbon dioxide content in groundwater. Spike-like anomalies of electrical conductivity correlate with local seismic events thus suggesting variations in groundwater dynamics.