Distribution of soil gas radon concentration in north-eastern Sicily (Italy): hazard evaluation and tectonic implications

Radon measurements in soil gases were carried out along the Tyrrhenian margin of north-eastern Sicily (southern Apennines of Italy), one of the most tectonically and seismically active areas within the central Mediterranean region. The collected data highlight an similar to NW-SE oriented zone located to the south of the Milazzo Peninsula marked by intense soil radon degassing. Concentrations of Rn-222 and Rn-220 were derived to be in the range of 0.69-81.3 kBq m(-3) and 2.63-123.48 kBq m(-3), respectively. The widespread radon release seems to be induced by the uprising of deep-originated fluids along faults and joints, and it is favoured by the high permeability of the outcropping alluvial Quaternary sediments. Moreover, the potential tectonic structure promoting the soil radon degassing may act as the "silent" on-land prolongation of the Vulcano-Milazzo fault zone (VMFZ), a transtensional tectonic element located in the Gulf of Patti and belonging to the Aeolian-Tindari-Letojanni System (ATLFS). The collected results are in accordance with previous studies showing the close relationship between regional degassing and tectonic activity. Periodical and continuous monitoring of radon emission over the area is considered of basic importance to better assess the radiological/health hazard for the population, which in this study was primarily evaluated from low to moderate in terms of first-level screening, as well as in view of possible development of the seismogenic process that can intensify the releasing of endogenous fluids.