Geogenic radon as geophysical tracer of active faults: the Fucino Plain (central Italy)

In geosciences, the analysis of the spatial distribution of radon (222Rn) concentrations in the shallow environment provides insights into a range of primary spatial/temporal geochemical/geophysical processes. Among the soil gases, 222Rn is considered a convenient fault tracer, because of its ability to migrate to long distances from host rocks, as well as the efficiency of detecting it at very low levels. In the scientific literature, many papers are focused on Rn as tracer of hidden faults, and reported Rn anomalies significantly higher than background levels along active faults and associated fracture zones (King et al., 1996; Ciotoli et al., 2007, 2014, 2016; Davidson et al., 2016). Evidences suggest that these anomalies can provide reliable information about the location and the geometry of active faults, and the width of the surrounding fracture zones (also if buried under the sedimentary cover) (Ciotoli et al., 2016, 2007; Seminsky et al., 2014). In this work, new soil gas measurements were carried out at different scales across known and inferred structural discontinuities in the Fucino plain (central Italy) in order to homogenise and densify the sampling reported in Ciotoli et al., 2007. Dataset has been re-interpreted by using new GIS and geospatial analysis techniques and discussed in the light of new seismic data interpretation (Cara et al., 2011). In particular, the correlation between the distribution of radon anomalies and the offsets measured along the San Benedetto-Gioia dei Marsi Fault (SBGMF) are discussed. Furthermore, new hypotheses are proposed regarding the link between radon migration and the process of fault evolution during the progressive linkage mechanism of several fault segments.