GNGTS 2013 - Atti del 32° Convegno Nazionale

other places, like the eastward fault termination close to Civita, finally making an extensive 2D-3D GPR survey to a Southern branch of the Castrovillari fault. In particular the acquisition of 3D data was done to analyze a wider area with a dense recording grids (Grasmueck et al. , 2005), in order to provide a data volume suitable to study the geological structure in their actual geometry. We obtained suitable a-priori information then used by the paleoseismologists to efficiently plan and drive the trench excavation. Geological outline. Geologists and seismologists consider both the Mt. Pollino and the Castrovillari faults as two active, but “silent” structures, anyway capable to potentially generate strong earthquakes. Thanks to geomorphological field observations, paleoseismological analysis and comparison with surface faulting events in the Apennines and nearby regions, the estimated Mmax could be about 6.5-7 degrees. The Pollino area is located in the Calabria region (Southern Italy) and divides the NW-SE trending Southern Apennines from the Calabrian Arc. A crustal extension during the Quaternary age affected the area, generating tectonic basins like the Northest Mercure Basin and the southern Morano – Castrovillari Basin. The area represents the most significant seismicity gap within the southern Apennines (Michetti et al. , 1997; Cinti et al. , 2002), like analogous “silent” structures in the Central Apennines (Galli et al. , 2008) because seismological data don’t show historical record of seismic events of M > 5. The W-NW “Pollino fault” and the N-S trending Frascineto/Castrovillari faults (Fig. 1), bound the hangingwall hosts named Morano – Castrovillari basin, filled by about 900 m of sedimentary units like marine rocks (upper Pliocene-lower Pleistocene) and continental deposits (middle Pleistocene to Holocene). These two faults are among the major Quaternary normal faults of the area showing paleoseismological evidences of late Quaternary activity (Michetti et al. , 1997; Cinti et al. , 1997, 2002). Recently, a seismic sequence including an earthquake of M = 5.0 (2012/10/26) struck in particular the western part of the region (ISIDe Working Group, INGV, 2010). Fig. 1 – View of the study area. The Castrovillari basin shows the main faults alignments with the red lines, highlighted by morphologic fault scarps. The orange points indicate the earthquake locations and magnitude (M > 2.5) occurred between 2011-2013, whilst the two orange stars represent two events with M > 4 (Mormanno, M = 5.0, Morano Calabro, M = 4.3), extracted by the Iside Database. The circles highlight the three principal survey sites on which GPR data were recorded during the project. 170 GNGTS 2013 S essione 1.2