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 faul ted blocks bounded by normal faults, mostly trending NW-SE, NNW-SSE an d NE-SW, which cut previous compressive structures. Such a structural setting is consistent with the focal mechanisms of the earthquakes whi ch often occur in this area. In this paper, three lithologically diffe rent normal fault-generated mountain fronts are analysed in order to a ssess the relations between their geomorphic features and active tecto nics. They border the Norcia depression (Sibillini Mts, Umbria), the A matrice-Campotosto plateau (Laga Mts, Lazio) and the Fucino basin (Mar sica 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 wi de fault escarpment, characterized by: (1) sharp slope breaks due to l ow angle gravity faults; (2) important paleolandslides; and (3) severa l fault scarplets on the piedmont belt affecting Quaternary deposits. The Amatrice-Campotosto plateau is delimited by the western slope of M t Gorzano which runs along a N20-degrees-W trending normal fault havin g a 1500 m throw. Minor parallel faults dislocate Quaternary landforms . Large-scale mass-movements also occur here. The Fucino basin was str uck by the 1915 Avezzano earthquake (I = XI MCS) which produced extens ive surface faulting along two parallel NW trending normal fault escar pments on the eastern border of the basin. There is paleoseismic evide nce including buried gravity graben in Late Glacial gravels and tecton ic dip-slip striations on Holocene calcitic crusts covering bedrock no rmal fault planes. These data suggest that active extensional tectonic s plays a major role in the slope morphogenesis of the Central Apennin es and they indicate the importance of geomorphic analysis in seismic zonation of this area.