222 Rn study throughout different seismotectonical areas: comparison between different techniques for discrete monitoring

n the frame of the geochemical monitoring of seismicity mainly aimed at deepening the relationships between active seismotectonics and fluid geochemistry, i.e. earthquake prediction, a 222 Rn study was accomplished. It is addressed to inter-calibrate in diverse tectonic settings different methods to measure radon in groundwater: Alpha Scintillation Method using Lucas Cells (ASM-LCC) and Gamma Spectrometry Method (GSM), adopting both the Charcoal Trap Method (CTM) by Active Charcoals Canisters (ACC) and the Beaker Marinelli (BM) sampling devices. The intercalibration occurred on the field as well as in the laboratory, to finally select the best-fitting to gather radon information in each situation. Three Italian areas were selected to verify radon behavior and background concentration in different seismotectonical, geo-structural and lithological settings: ancient metamorphosed rocks – quiescent faults (Eastern Alps), carbonate foreland – active faults (Gargano) and quiescent volcanic structure overlapping a carbonate basement – swarm seismic activity (Colli Albani). The high radon concentration variability and the factors affecting radon behavior in groundwater (i.e. carrier gases presence, convection along fault systems, lithology influence, etc.) strongly constrain the measurement method to be adopted.
The results point out apparently that the ASM-LCC method may be useful for expeditious and quick response of groundwater radon concentration during geochemical surveys aimed at grossly detecting the presence of tectonic structures, the deepening of circulation or the peculiar geological features linked to the presence of U-Th minerals. This method is not reliable for accurate measurements, while the GSM methods showed low standard deviation (higher precision with respect ASM-LCC) and accurate radon measurements. Finally, a customized DINCE Standard Radiactive Source (DSRS) was set up, and first used for the efficient estimation of the ING available Lucas Cells. A calibration factor for each ING Lucas Cell was defined and the most critical aspects of the ASM-LCC method revised.