Neotectonic evolution and Geomorphology of the Cascia and Norcia depressions (Umbria-Marche Apennine)

Abstract

The neotectonic and geomorphological evolution of the Norcia and Cascia depressions, which are part of a particularly important sector of the Umbria-Marche Apennine Arc, is illustrated. After -the main compressive phase (end of the lower Pliocene-beginning of the middle Pliocene), which has determined a tectonic pattern consisting of three structural elements overlapping at least in part over one another (upper overthrust, lower overthrust, foredeep deposits), a long period of relative tectonic quiescence was established which lasted until the lower Pleistocene. In this area, during the above said time interval, a low relief energy landscape (« paleosurface ») was modelled, probably also in relation to climatic conditions favorable to areal erosion. The above «paleosurface » has subsequently (lower-middle Pleistocene) been uplifted and dislocated by normal faults connected with the presence of a tensional stress field. The main new dislocations stretch with the Apennine trend and, together with other transverse faults (probably following previous strike-slip faults), have dismembered the previous structural pattern into blocks. The depressions of Norcia and Cascia correspond to two of these downthrown elements. The extensional tectonic phase has continued up to the present time as demonstrated by the direct faults, which dislocate the filling deposits of the depressions, and the seismic activity of the area, which fits very well the tensional type framework.