GNGTS 2013 - Atti del 32° Convegno Nazionale

Two sections, named Castrovillari A, were centered at the southward projection of the outcropping F1 fault trace. The 5 m spacing line allowed to investigate the subsurface down to 30 m; a more detailed line, reaching the depth of 12 m, was acquired using a 2 m spacing. Resistivity values range between less than 50 Ohm · m and more than 900 Ohm · m. The outcrop exposed by the road cut (Fig. 2e) shows a sequence of alternating conglomerates and sands that can be typically associated to high and relatively low resistivity values respectively. Abrupt lateral changes in the resistivity values can thus strongly suggest a tectonic contact between high impedance units. The 2 m spaced array provides a better resolution of the central sector, showing two different bands of low-resistivity: the first one between 32 and 40 meters and at a depth of 5-8 m, and another one between 40 and 60 meters and from surface to 5 m of depth. These two areas are clearly offset by another secondary discontinuity (F3) located in the footwall of the main fault. The third line of the site, marked as Castrovillari B, runs some tens of meters SW of line A and was acquired to verify the presence of fault displacement (F2 fault) within recent fluvial deposits. In this area fine-grained material is present at the gully edge wall. Fig. 2d shows a 2 m spaced section reaching 14 m of depth. Resistivity values range between more than 45 Ohm·m and less than 400 Ohm · m. A high resistive zone is present in the eastern sector of the section, between the distance of 32 and 56 m, at a depth of 3-7 m. We associate this zone to gravel layers, coarser than the sandy and silty deposits, the latter typically characterized by smaller resistivity values. This tabular body is abruptly cut by a steep SW dipping plane (as better highlighted by the dipole-dipole array acquisition; not in figures) that can be interpreted as due to fault displacement. Offset cannot be not easily measured, even if from the dipole - dipole array a 5-6 m of vertical offset can be inferred. F1 fault has been trenched for paleoseismological analyses. The stratigraphy is composed of a strongly cemented conglomerate, the oldest unit exposed, and a succession of alluvial and colluvial deposits (silt, clayey silt, conglomerate and gravel). The trench shows a fault zone composed by two main, 1 m spaced, 70° dipping fault traces displaying dip-slip displacement. The fault zone is aligned with the fault outcropping on the retreated valley edge and define a N 160°-165° oriented trace. The analysis of the stratigraphic and structural setting allowed to recognize at least three distinct paleoearthquakes. Although uncertainties affect the values of offsets across the faults, due to channeling and slope deposition, slip per event is larger than 0.6 m (earthquake M>>6). Preliminary datings confirm the timing of the paleoearthquakes previously recognized by Cinti et al. (1997; 2002): best estimate around V-VI century A.D. (no later than X century). Although evidence are uncertain, the age of a possible younger earthquake is set between XIII and XV century A.D. The Pollino fault. The Pollino fault (Fig. 1b) is a WNW-trending structure characterized by an impressive range front with more than 1400 m of relief. The fault hangingwall hosts the Castrovillari basin, whose sedimentary fill reaches its maximum thickness of about 600 m, filled in with upper Pliocene to lower Pleistocene marine rocks and about 300 m of middle Pleistocene to Holocene continental deposits. The field survey performed along the Pollino fault concentrated the efforts in the previously un-investigated eastern portion of the Pollino scarp. This latter is less studied than the western sector, where data on the fault activity, previously collected through paleoseismological investigations (Michetti et al. , 1997), indicate two probable paleo-events, dated respectively at VI – XII century A.D. and XIII – XV century A.D. We selected the studied site as suitable for geological and subsurface investigations in order to acquire new data on the geometry of the fault and on its activity in time. We thus focused our analysis at the Civita site, along the Pollino scarp (Fig. 1b). In this site we observed the outcropping fault plane of the Pollino fault along two walls of a dismissed quarry, orientated perpendicular to the fault trace. A wide zone of tectonic 111 GNGTS 2013 S essione 1.1