FAULT-GENERATED MOUNTAIN FRONTS IN THE CENTRAL APENNINES (CENTRAL ITALY) - GEOMORPHOLOGICAL FEATURES AND SEISMOTECTONIC IMPLICATIONS

The morphotectonic framework of the Central Apennines is given by faulted blocks bounded by normal faults, mostly trending NW-SE, NNW-SSE and NE-SW, which cut previous compressive structures. Such a structural setting is consistent with the focal mechanisms of the earthquakes which often occur in this area. In this paper, three lithologically different normal fault-generated mountain fronts are analysed in order to assess the relations between their geomorphic features and active tectonics. They border the Norcia depression (Sibillini Mts, Umbria), the Amatrice-Campotosto plateau (Laga Mts, Lazio) and the Fucino basin (Marsica Mts, Abruzzi). The Norcia depression is bounded by a N20-degrees-W trending normal fault to the east and by a parallel antithetic fault to the west. The main fault has a 1000 m throw and gives rise to a wide fault escarpment, characterized by: (1) sharp slope breaks due to low angle gravity faults; (2) important paleolandslides; and (3) several fault scarplets on the piedmont belt affecting Quaternary deposits. The Amatrice-Campotosto plateau is delimited by the western slope of Mt Gorzano which runs along a N20-degrees-W trending normal fault having a 1500 m throw. Minor parallel faults dislocate Quaternary landforms. Large-scale mass-movements also occur here. The Fucino basin was struck by the 1915 Avezzano earthquake (I = XI MCS) which produced extensive surface faulting along two parallel NW trending normal fault escarpments on the eastern border of the basin. There is paleoseismic evidence including buried gravity graben in Late Glacial gravels and tectonic dip-slip striations on Holocene calcitic crusts covering bedrock normal fault planes. These data suggest that active extensional tectonics plays a major role in the slope morphogenesis of the Central Apennines and they indicate the importance of geomorphic analysis in seismic zonation of this area.