Relationship between soil CO2 flux and tectonic structures in SW Sicily

The identification and characterization of seismogenic structures in southwestern Sicily is an open debate both for the geological-structural complexity of this sector and the scarce seismicity as well. In addition, clear morphological evidence of tectonic structures is limited. Besides the geophysical methods, the study of the spatial distribution of soil CO2 flux is a valid methodology to investigate the position and geometry of buried active faults. Indeed, active tectonic structures are channels with high permeability through which deep fluids can migrate toward the atmosphere. Therefore, the alignment of high degassing areas can reveal the presence of preferential ways of rising fluids (i.e. faults). We applied this methodology in SW Sicily in the surrounding of the area hit by the 1968 seismic sequence and in three other areas where evidence of active deformation has been recognized. Furthermore, to investigate the origin of emitted fluids, we measured the carbon isotopic composition of the soil CO2 in some high emission sites. The results showed high spatial variability of soil CO2 fluxes with values ranging from 1 to 430 g m(-2) d(-1). The areal patterns of soil CO2 fluxes in all the areas reveal a strong influence of the main tectonic structures and active deformations on soil CO2 emissions. The range of isotopic data and the distribution of soil CO2 fluxes suggest a supply of deep fluids through the active tectonic structures.