Displacements on a slope affected by deep-seated gravitational slope deformation: greci slope (Lago, Calabria, Italy)

Abstract

The study zone extends over an area of ca. 3.5 km2 in the Tyrrhenian Coastal Chain, northern Calabria, Italy. It includes an east-facing slope for all its length and the valley floor of the Licetto Torrent that drains to the Tyrrhenian sea. The complex Geology is made of different thrust nappes forming an allochtonous tectonic building piled up in Oligocene - Lower Miocene, upon which Quaternary alluvial and colluvial deposits lie. Deep-seated gravitational slope deformation of Sackung type affects the Greci slope (Lago, Calabria, Italy). The study faces this complex phenomenon by means of geological, structural, geophysical, geomorphologic, geotechnical, historical and dendrochronological tools. Monitoring of surficial and deep-seated displacements is one of the fundamental investigations. GPS measurements, performed since 1996, depict a complex scenario of displacement, consisting in different sectors moving at rates ranging from less than 0.2 cm/y to 10 cm/y. Measurement of deep-seated displacements have been performed along two inclinometric verticals both 100 m deep. At northern site displacements consist in an upper section 28 m deep moving at a steady rate of ca. 1 cm/y; at the southern site displacement rate is much larger, ca. 10 cm/y, and rather uniform, down to a depth of 60 m. These results provide kinematic data regarding the present evolution of the phenomena, necessary for developing a geotechnical model of the unstable slope and, consequently, to define the most probable collapse scenario.