GNGTS 2013 - Atti del 32° Convegno Nazionale

MORPHOMETRIC ANALYSIS OF THE WESTERN ASPROMONTE MTS. (SOUTHERN CALABRIA, ITALY): EVIDENCE FOR ACTIVE TECTONICS C. Pirrotta, M.S. Barbano, C. Monaco Dipartimento di Scienze Biologiche, Geologiche e Ambientali, Università di Catania, Italy Introduction. Fluvial network development and organisation are influenced not only by climatic and lithological factors but also by tectonic movements, such as regional uplift, subsidence and fault activity causing local landscape modification. Rivers are the most sensitive geomorphological elements capable to record recent tectonic activity, indeed when perturbed by landscape changes they leave their equilibrium state and lose their hierarchical organization. Then, rivers tend quickly to restore equilibrium producing anomalous segments and also create typical features such as fluvial capture, deflections, abandoned channels and so on. Thus, geomorphological and morphometric studies of fluvial network and associated hydrographic basin allow analysing landscape modifications and they can provide information about active tectonics. Numerical calculation of geomorphological indexes (Keller, 1986; Cox, 1994) applied to rivers can be a basic reconnaissance tool in order to determine the influence of faults on the hydrographic network and to identify areas with rapid tectonic deformation (Verrios et al. , 2004). In southern Calabria, NE-SW to NNE-SSW striking and west-dipping normal faults dominate the neotectonic deformation scenario (Fig. 1). Our study focus on the evaluation of active tectonics in the Aspromonte Mts. area by geomorphological, morphometric and morphostructural analyses of two rivers and their basins: the Petrace Fiumara and the Catona Fiumara. These rivers run from the Aspromonte ridges towards the Tyrrhenian Sea and are intercepted by normal faults, whose activity has been recorded by drainage network. Geological setting. The Aspromonte Mts. are located in the southern part of the Calabrian Arc which connects the Apennines and the Sicily orogenic belts (Fig. 1). The Calabrian Arc, which includes Calabria and the north-eastern side of Sicily, is a forearc terrain which was em- placed to the south-east during north-westerly subduction and roll-back of the subjacent Ionian slab (Malinverno and Ryan, 1986; Neri et al. , 2012). During the Late Pliocene-Quaternary, contractional structures of the hinterland part of the forearc were superseded by extensional faults which caused its fragmentation into structural highs and shallow marine sedimentary basins, including the Mesima and Gioia Tauro basins and the Messina Straits (Ghisetti and Vezzani, 1982). At present, an active swarm of normal faults runs along the Calabrian Arc and is associated with strong seismicity (Monaco and Tortorici, 2000). Current WNW-ESE-trend- ing crustal extension is documented by focal mechanisms of earthquakes (CMT and RCMT Catalogues; Neri et al. , 2004), structural studies (Tortorici et al. , 1995; Jacques et al. , 2001; Ferranti et al. , 2007) and geodetic velocities (Mattia et al. , 2009; D’Agostino et al. , 2011). Since the Middle Pleistocene, extensional tectonics has been coupled with intense regional uplift which developed flights of marine terraces (Ferranti et al. , 2006 and references therein). Active tectonics in the Calabrian Arc is attested by the uplift of the coast (Westaway, 1993; Ferranti et al. , 2007), by landscape imprint (Guarnieri and Pirrotta, 2008), structural evidence (e.g. Tortorici et al. , 1995; Jacques et al. , 2001; Aloisi et al. , 2012) and by the frequent occurrence of strong and moderate earthquakes (Rovida et al. , 2011). Southern Calabria was hit by disastrous earthquakes and long seismic sequences during historical times (1659, February-March 1783, 1894 and 1908 earthquakes), that caused thousands of fatalities and several secondary effects including tsunamis (Fig. 1). Although the dramatic impact of these earthquakes on the region, the association with their causative faults is still debated and they are often related to different seismogenic sources (e.g. Valensise and Pantosti, 1992; Jacques et al. , 2001; Galli and Bosi, 2002; Basili et al. , 2008; Aloisi et al. , 2012). The 1783 sequence (mainshock M ~ 7; Rovida et al. , 2011) changed the Aspromonte Mts. landscape triggering several landslides, liquefactions and ground fracturing. Long and continuous fractures, 103 GNGTS 2013 S essione 1.1