GNGTS 2013 - Atti del 32° Convegno Nazionale

The marine terraces analysis enables to determine an evaluation of the long-term uplift-rate involving the region since the Middle-Pleistocene (~600 ka). Along the Ionian coast, starting from the Alcantara River mouth the values of uplift-rate switch from 0.9 to 1.1 mm/a towards the NE, near Messina area (Catalano and De Guidi, 2003). Between this two localities the uplift-rate values reach a maximum value of about 1.7 mm/y, ascribable to the Taormina fault activity. Along the western side of the Tyrrhenian coast of the PMB a sharp variation of the long- term uplift-rate has been found between the Capo d’Orlando and San Marco d’Alunzio areas. In particular, in correspondence of the PBM side has been calculated an uplift-rate of 1.1 ± 0.13 mm/a switching to 0.76 ± 0.05 mm/a to the south (inset in Fig. 1b). This 0.3-0.4 mm/y gap is significantly in accordance with the short-term deformation rate (0.4-0.5 mm/a) calculated on the basis of the above discussed structural analysis. In addition has been calculate the variation of the uplift-rate between the PMB and the southern area, getting a reconstruction of the trend in time of the deformation-rate along the studied faulted zone. As constrained by the obtained data, after an early decrease, lasted until OIS 7.1 (200 ka), starting from the period elapsing between this latter and the OIT stage 3 (125 ka) the deformation-rate along the faulted zone increased from 0.15 to 0.45 mm/a. Morphometric analysis. A morphometric analysis regarding the drainage system of the south-western sector of the PMB has been carried out. This analysis firstly consisted of a semi- quantitative study of the fluvial network of main drainage basins, roughly NW-SE oriented and flowing to the NW. In addition to defining the relationships between fluvial network and both the faults of the region and the rejuvenated Holocene fault segments, a morphometric characterization of basins has been performed, based on appropriate morphometric indexes generally exploited for tectonic geomorphology studies. The obtained data, as a whole, enable to understand how the Late Quaternary tectonic deformation has driven the landscape evolution and the fluvial network arrangement. Basins asymmetry. Since the studied area is affected by a NW-SE oriented SW-dipping normal faults system, defining several faulted blocks, it was reasonable expecting a tectonic tilting towards the north-east. In order to detect and numerically evaluate the tectonic tilting of the region, it was applied an useful index employed in region involved in neo-tectonic process- es (Hare and Gardner, 1985; Cox, 1994); it is represented by the Asymmetry Factor ( AF ) of the drainage basins (Hare and Gardner, 1985). In the studied sector of the PMB , regardless of hi- erarchical order, were analysed 10 basins in order to cover as much as possible the investigated area. The results (<50%) suggest an almost significant asymmetry of basins to the right (facing downstream) constraining a NE-ward tectonic tilting (Fig. 2a). Only a small basin shows an AF value slightly more than 50%. The valleys asymmetry, associated with the NE-ward tilting of the faulted-blocks, testifies the tectonic deformation cumulated along the NW-SE orient- ed, SW-dipping, normal faults. Another asymmetry index is represented by the Transverse Topographic Symmetry Factor ( T ) (Cox, 1994), whose obtained values confirm the AF data, providing a more detailed distribution of asymmetry along the basins (Fig. 2a). Across the faulted belt several NE-directed swath profiles have been realized (Fig. 2b). It is possible to firstly appreciate the NE-ward tilted summit surfaces of the landscape, dislocated by SW-dipping faults, and the clear NE-ward asymmetry of the transverse subsequent valley, showing their northern flank steeper than the southern one. Fluvial network arrangement analysis. The fluvial network analysis has been performed for the main basins lying on the south-western side of the PMB and flowing towards to the Tyrrhenian sea. After the reconstruction of the fluvial network, the stream system has been hierarchized as proposed by Strahler (1958). Afterwards sectioning the streams in several trunks, each fluvial hierarchical order, from 1 to 7, has been separately processed. The same procedure has been followed for the tectonic structure that lie inside the studied area and for the Holocene fault scarps recognized within the aforementioned faulted zone. Firstly, the analysis 178 GNGTS 2013 S essione 1.2