The Southern Boundary Of The Seaward-Sliding Eastern Flank Of Mt. Etna: Evidences On Active Faults In Urban Areas From Soil Gases And Satellite Data

Abstract

From October 2008 to November 2009, soil CO2 and Rn surveys have been performed, in order to get insights upon active tectonic structures in a densely populated sector of the South-Eastern flank of Mt Etna, which seems to be involved in the flank dynamics, as highlighted by satellite data (INSAR). The investigated area extends about 150 km2, in an area, where INSAR data detected several lineaments not known from geological surveys. The method adopted to perform the 345 soil CO2 measurements is the “dynamic concentration” method (Gurrieri and Valenza, 1988; Camarda et al., 2006), which provides a proxy for soil CO2 fluxes. The gas measurements have been performed along transects roughly orthogonal to the lineaments, with measurement points spaced about 100m. The method appeared more efficient than a regular grid, which would have requested much more measurements and a time-consuming field work. CO2 data show the highest values, along each transect, very close to the lineaments evidenced by INSAR observations. Anomalous values also occur in correspondence of eruptive fractures. In some portions of the investigated area, rather broad anomalies are observed, and this would imply that, instead of a single well-defined lineament, a wider fault zone probably exists. A set of both CO2 and Rn measurements, performed at about 900m of altitude, are worth of note, because they allow identifying the lengthening of detected lineaments at higher elevation, where the INSAR data are poorly informative. Finally, at the base of the volcanic edifice, the soil gas anomalies strikingly define the active structures until almost the coastline through the northern periphery of Catania town. The coupling of the two methods thus revealed as a powerful tool to detect buried active structures, which conversely do not show significant field evidences.