MOUNTAIN SLOPE DEFORMATION IN THE FAULT-BOUNDED WESTERN SLOPE OF THE MAIELLA MASSIF (CENTRAL APENNINES, ITALY)

Relationships between tectonic framework and gravity-driven phenomena have been investigated in the Maiella Massif (central Apennines), characterised by high mean elevation (Mt. Amaro, 2793 m asl) and significant topographic stress. The N-S oriented Maiella anticline lies in the easternmost part of the Apenninic chain. Here, a first-order normal fault with a maximum downthrown of 3.5 km ca. separates the western, calcareous reverse slope from the morphologically depressed Caramanico Valley, filled by Mio-Pliocene flysch and Quaternary, continental deposits. The whole south-western Maiella area is affected by ongoing deep rock slope deformation, pointed out by a main ridge-top depression (about 4 km long), secondary crest line displacements, down-hill and up-hill facing scarps and local convex slope profile. The deformation process, which involves an area of 16 km², has developed in correspondence to the anticline axial culmination and is bordered eastward by a NNW-SSE oriented, dextral, strike-slip fault zone, parallel to the orientation of the main geomorphological signatures. Pattern of open fractures and trenches in the uppermost section of the slope clearly testify active tensile stress conditions; furthermore, the presence of different types of landslide and talus deposits indicate the present rock slope deformation activity. Within such a context can be framed the occurrence of a huge prehistoric massive rock slope failure with typical rock avalanche features, which affected part of the deforming slope. Rock mass characterisation and trench investigation have been carried out in order to better understand the deformation mechanism and kinematics and to evaluate their relationships with the anisotropies linked to the inherited structural pattern. The collected data were the base to construct the geological model of the rock slope deformation process, successively validated through the results of a numerical model based on finite difference method. The Maiella western, fault-bounded slope can be framed in a compound listric sagging-type phenomenon, whose onset and evolution have been determined by the high topographic stress and by the presence of several pre-existing anisotropies within the rock mass represented by intensive jointing also due to the Plio-Quaternary tectonic activity.