GNGTS 2017 - 36° Convegno Nazionale

136 GNGTS 2017 S essione 1.2 The Crati Graben Detachment fault (CGDF). A southern structure, hereinafter referred to as the Crati Graben Detachment Fault (CGDF), was reconstructed in the field for nearly 60 km, along the eastern sides of the San Donato di Ninea Metamorphic core and of the Catena Costiera Calabra (Fig. 1). The CGDF bounds to the west the Castrovillari and Crati Quaternary basins and its surface expression can be recognized, moving from north to south, in the S. Sosti- Saracena Fault and in the San Fili - San Marco Argentano fault. Both these faults show normal kinematics with slightly-oblique component. In the central part of its trace, it is crossed in W-E direction, by a commercial seismic reflection line, availbale for reasearch purpose (ViDEPI, 2017) extending eastward to the Sila slope (Fig. 3a), which was interpreted and converted in order to better constrain the CGDF geometry in the subsurface and its associated system of extensional fault (Fig. 3b,c). This section confirms that the CGDF reaches the surface along the eastern slope of the Catena Costiera Calabra and dips eastward, with a complex trajectory, but at an average dip- angle of 30° (Fig. 3c). As well as providing a clear image of the extensional fault pattern, the line also allowed us to distinguish the main units stacked in northern Calabrian arc (Fig. 3b,c) that here are represented by Quaternary syn-extensional deposits and Miocene siliciclastics successions, overlying the crystalline basement. The thickness variations affecting the Quaternary succession due to the main normal faults, confirm their syn-sedimentary activity. Inmost part of the line, the reflections TBa (top of the basement), Mev (Messinian evaporites), TPl (top of the Pliocene succession) and TGe (Top of the Gelasian clays) are confidently recognised (Fig. 3b). At pseudo-depths increasing eastward from 0.3 to 1.5 sec twt, all of these reflectors interrupt onto an east-dipping prominent reflection (shp 240-400), whose surfacing fits the outcrop of the Torano-Martorano normal fault (TMF) mapped in the field (compare Figs. 3a, and 3b). Other low-angle reflections, aligned with the TMF, can also be detected. We interpret these features as the trace of the CGDF which plays the role of a deep boundary for all the extensional fault set. The seismic trace of the fault gradually shallows westward and emerges at the western edge of the basin along the San Fili - San Marco Argentano fault. On the deepest east side of the section, certain weak signals consistent with the down-dipping prosecution of the CGDF, occur at 2.5-3 sec twt. The subsurface geometry of the syn-tectonic deposits, their structural setting and the detailed review of their stratigraphy, suggest that the high-angle normal fault set, branching upward from the CGDF is, also in this case, characterized by a progressive eastward-younging trend with the recent-most splays bounding the western edge of the present Crati valley floodplain. The Seismic interpretation makes possible also a rather precise assessment of the cumulative displacement due to the CGDF and to its major synthetic splays, providing a minimum value of 4000 meters in the central part of the structure. The lack of a robust dataset of instrumental relocated earthquakes, prevents the possibility to test convincingly the seismogenic role of the CGDF in the study area. However, the compatibilty of the available hypocentral determinations with an east-dipping moderately inclined source, has been recently evidenced by Brozzetti et al. (2017b). The Papasidero-Saracena Transfer Zone (PSTZ). Poor data are available on the N110E striking transfer zone connecting the LCDF and the CGDF. Preliminary results of our mapping suggest that it corresponds to a nearly E-W striking alignment of high-angle faults, dipping to north, then sub-parallel but antithetical to the well-known Pollino Fault. The structural data collected on these transfer faults, record normal to normal-dextral movements. In correspondence of this regional tectonic line, the axial zone of the active extensional belt, undergoes an abrupt shift of nearly 20 km, from the Mercure-Lao sector (north of the PSTZ) to the Castrovillari-San Sosti-Crati basins (south of the PSTZ).