New evidence for the form and extent of the Pernicana Fault System (Mt. Etna) from structural and soil–gas surveying

A multidisciplinary study based on structural and soil–gas surveys was carried out in order to investigate the relationship between soil CO2 degassing and the tectonic setting of the lower northeastern flank of Mt. Etna volcano. The results show that anomalous soil CO2 emissions occur mainly along faults trending WNW–ESE and also where these faults intersect the other main fault set (trending NE–SW) that displaces the study area. In particular, anomalies in CO2 degassing were revealed both along the Pernicana Fault and along another fault (Fiumefreddo Fault) which may represent the prolongation of the former towards the Ionian Sea coast. In the areas where these structures show evident surface faulting, they are all characterised by left-lateral displacements and aseismic creep behaviour. Furthermore, the geochemical survey revealed that these faults join in an area devoid of geological evidence of surface faulting and continue underneath an apparently unfaulted alluvial cover near the coastline. In the light of these findings, we suggest that the Pernicana and Fiumefreddo Faults are discrete segments of a near continuous left-lateral shear zone affecting the whole north-eastern flank of Mt. Etna as far as the Ionian coast.