The Mt. Pollino Fault (southern Apennines, Italy): GPR signature of Holocenic earthquakes in a “silent” area

The Mt. Pollino Fault Zone is located in the northern sector of the Calabria region (southern Italy). It represents a segment between the southernmost part of the Apennines and the Calabrian Arc. In the Pollino area, seismic events of magnitude > 5 are not currently reported in literature and within the seismic catalogues, therefore this “gap” zone has been defined “silent”. Due to the geomorphological, geological and paleoseismological evidences of Quaternary faulting, the Pollino-Castrovillari faults are considered active, as demonstrated also by some recent reactivations, that have generated several earthquakes of moderate magnitude (Mmax ≤ 5.0) in a north-western sector, near Mormanno (Mercure Basin) and Morano villages (Morano-Castrovillari Basin). Therefore, the studied area retains many uncertainties in the definition of the seismic hazard. With these premises an integrated project started in 2012 (Agreement INGV-DPC 2012-2013, Project S1) aims to improve the base-knowledge for assessing the seismogenic potential. Among the different geological studies, the project encompasses the GPR fault imaging on several sites, having different goals: 1) define the location and the geologic characteristics of active faults; 2) detect new evidences of “recent” faulting; 3) correctly locate these structural elements on a geologic map; 4) support further paleoseismological surveys. A first 2DGPR survey was done at the Grotta Carbone site, about 4 kilometers from Castrovillari, for which some trench logs were already available, in order to “image” the fault zone and to provide a GPR data calibration using the stratigraphic information. The results of the radargrams interpretation show a characteristic GPR signature of the tectonic structures and faulted units and a different dielectric behavior among the units located across the fault, revealing an excellent matching with the available geological data. Clear tectonic features and their vertical offset between layers have been highlighted within the fault zone. The stratigraphy of the trenches have been extended, along the fault and in depth, providing new useful information essential for a better definition of the seismic hazard of the area and for a future 2D/3D dataset extension across other sites.