GNGTS 2013 - Atti del 32° Convegno Nazionale

also a different character of the direct arrivals. The different geological units can be therefore interpreted and mapped, and some parameters can be extracted by the radargrams, like the layers thickness, bedding and the fault offset, of about 1 meter at 23 m along the profile (white arrow on the right in Fig. 2a). The 300 MHz radargram here reported for the Castrovillari survey shows a good S/N ratio and signals suitable for an efficient geological interpretation (Fig. 3a). This can be ideally divided in four sectors, having different characteristics: in the SW sector between 0-20 m (black box) some W-SW dipping reflectors are visible over a sub-horizontal unit at about 2 m of depth from the topographic surface. That geometry is compatible with a transversal section of the lentiform sedimentary bodies belonging to N-S alluvial fan: such layers are also well-visible on outcrops close to the survey site. The red box highlights an area characterized by the presence of some diffractions (in unmigrated data) and an interruption of the lateral continuity among the reflectors, which represents a peculiar geophysical signature of a fault. The diffractions are probably generated by the high dipping “fault plane” and the lateral stratigraphic contact between two materials having different dielectric properties, probably including cemented filling and/or cemented “blocks” within the faulted units (like in the outcrop picture in Fig. 3b).The fault is highlighted also by the different electrical response of the subsurface within the foot-wall and hanging-wall sectors, and by the stronger signal attenuation compared with the surrounding areas. The unit enclosed in the green box (Fig. 3a) is high reflecting with sub-horizontal layers, gently NE-dipping: this is interpretable as a sort of “bedrock”, probably related to a cemented unit. Finally, some weak reflecting reflectors are imaged in the Eastern sector of the radargram (fault hanging-wall, orange box about between Fig. 3 – 2D and 3D GPR data recorded on the Castrovillari site. a) Un-migrated 2D profile shows different areas within the dashed boxes, where the fault zone, characterized by a well defined signature, has been highlighted by the red one. b) Field picture reporting the fault on the outcrop. c) The 3D data show both the fault located at about 10 m along the GPR volume (X axis), and the different units detected in this complex site, like the shallow backfill layers and the colluvial/alluvial deposits corresponding with the attenuated side. 173 GNGTS 2013 S essione 1.2