Landslide susceptibility assessment in the southern sector of the Tammaro River basin (Italy)

Numerous methods have been proposed in literature for the landslide susceptibility assessment at basin scale using Geographical Information Systems (GIS). Among them, statistical methods have became increasingly popular in recent years. In particular, the Homogeneous Territorial Unit (HTU) method [DE VITA et al., 1994; GUIDA et al., 1996; CALCATERRA et al., 2010] has been applied in this work, which is well suited to problems of slope stability in structurally complex formations [ESU, 1977]. HTU method was applied to the southern sector of the Tammaro River basin, which corresponds to the municipalities of Paduli and Pietrelcina, in the southern part of the Apennines fold-and-thrust belt (Campania Region, Italy). From a geological point of view, this area consists of argillitic-marly-calcareous and argillitic-marly formations, known as "Varicoloured Clays", a structurally complex formation [ESU, 1977], well-known in literature for its susceptibility to landslides. The area of interest includes about 73 km2 of hilly territory, where 303 landslides, divided in 127 earthflows, 87 rotational/translational slides and 89 earth slides-earthflows, have been mapped, at 1:5.000 scale, by means of field survey and stored in a GIS-database. Moreover, geolithological and geomorphological maps (at 1:10.000 scale), as GIS-layers, were used to implement the homogeneous domains for the statistical analysis. Such domains represent specific mapping units, called HTUs, which define the classification of each slope-instability factor into four classes, stored into a single map, or layer. By means of the overlay of the HTU map and the landslide-inventory map, the susceptibility assessment is then extended to non-landslide areas by applying a statistical method.