Morphotectonic characterization of the quaternary intermontane basins of the Umbria-Marche Apennines (Italy)

In the axial zone of the Umbria-Marche Apennines, several fault-bounded intermontane basins (i.e., Colfiorito, Norcia, Castelluccio, and Leonessa) were generated at the end of Lower Pleistocene. The analysis of the master fault of the basins, the relicts of planation surfaces and the drainage network arrangements, allowed us the improvement of knowledge on the Pleistocene morphotectonic evolution of those basins. Morphometry and geostatistics of the topography have been performed to obtain indexes suitable for assessing the role of faults displacements on the landscape development. Furthermore, a gravimetric analysis realized along some basins has furnished new data on their sedimentary infill. The basins are filled by Pleistocene to Holocene fluvial-lacustrine coarse-grained deposits, and the bedrock consists of Jurassic to Miocene limestone and marls belonging to the Umbria-Marche succession. Several historical and instrumental highly destructive earthquakes occurred in this area: January 14, 1703 (X MCS, M = 6.6); September 19, 1979 (Ms = 5.9, focal depth of 6–8 km); September 26, 1997 (Mw = 6.0, focal depth of 6–8 km). Faults and earthquake focal mechanisms are compatible with a predominant NE–SW extension, but strike-slip and reverse mechanisms have been also documented. The fault activity appears to have had a predominant role in controlling the sedimentation processes inside the intermontane basins, as well as in controlling their Pliocene to Quaternary evolution.