Results of monitoring 222Rn in soil gas of the Gulf of Corinth region, Greece

Within the framework of the European projects GAÏA and CORSEIS, dedicated to the study of the rift of Corinth, various geophysical and geochemical monitoring had been performed between 1995 and 2002 for the search of crustal transients and earthquake precursors. We present here the monitoring of 222Rn activity in soils, which are expected to carry information on underground fluids transport mechanisms. In order to identify transient anomalies, possibly correlated with seismic activity, continuous long-term monitoring is needed, and the background level is to be assessed for each measurement site. We discuss the methodological constraints (probes, installation, and site effects) and present the first results on the magnitude of radon variations with time. Radon time-series in soils gas appear to be very site-dependent: background levels, yearly cycle and spurious signals differ as the result of multiple local effects (meteorological disturbances, permeability of soils, etc.).