Central Calabria

Conventional methods used to detect slope instability and map geomorphologic processes, especially in mountain areas, can benefit from remote sensing analyses, e.g. optical and radar satellite data. We illustrate the contribution of Persistent Scatterer Interferometry (PSI) analyses and photo-interpretation for the updating of pre-existing landslide inventory maps in mountain areas, through the case study of Central Calabria, located in southern Italy with an extension of 4,470 km 2 . We used 108 ENVISAT ascending images (20 m ground resolution) acquired in 2003-2009 and processed with the PSP (Persistent Scatterer Pairs) technique, 1 optical image acquired by SPOT satellite (2.5 m resolution), and digital orthophotos with 1 m resolution covering the whole investigated area. All these data were integrated and combined with additional ancillary information (e.g. topographic, geological and land use maps). 980 landslides (23.9% of pre-existing inventory) were updated by means of PSI information and 64 new landslides were also detected. The state of activity and the intensity of these landslides were also updated and/or evaluated, showing that 22% and 2% of the updated inventory include active (919 landslides) and reactivated (93 landslides) phenomena respectively. The outcomes of the integrated radar-interpretation and photo-interpretation methodology for Central Calabria and its operative usefulness for civil protection authorities represented a valuable proof of the reliability of this approach for updating landslide inventory maps in mountain areas at regional scale. 2 CENTRAL CALABRIA (ITALY) 2.1 Geological and geomorphologic background The investigated area is the central part of the Calabria peninsula in Italy and includes part of the provinces of Cosenza, Catanzaro, Crotone and Vibo Valentia, with a total area of 4,470 km 2 (Fig. 1). Most of the outcropping basement is composed of Hercynian and Alpine crystalline and metamorphic allochthonous complexes, with associated Eocene and Lower Neogene sedimentary sequences (Van Dijk et al. 2000). Along the internal side of the Calabrian Arc, Mesozoic carbonate rocks  similar to the Apennine allochthonous units  crop out in windows below this basement. The contact between the basement units is overlapped at a low angle, obliterated by successive high-angle faults. Terrigenous Tertiary sequences are present as remains along the over-thrust contacts between these basement units and also as tectonic wedges along the fault zones at a higher angle. All these rocks are crossed by a complex group of high-angle faults, which can be organized in major systems and patterns, partly correlated to transcurrent faulting (Van Dijk et al. 2000). The geological structure is characterized by low-angle thrusts, dissected by high-angle faults with oblique movement components (Guerricchio 2004). The geomorphologic setting is characterized by widespread slope movements. In particular, several slow moving slides and complex slide-flows can be recognized and, secondarily, severe erosion and superficial rapid slope movements. Earth slides involve metamorphic rocks and earth flows affect Pliocene deposits. Moreover, landslides generally show recent morphologies, indicative of new activations. Along the eastern border of the Coastal Chain, largescale and deep-seated gravitational landslides can also be recognized (Iovine et al. 2006). 2.2 Pre-existing landslide inventory map The official landslide inventory map available for Central Calabria is part of the Hydrogeological Setting Plan (PAI Piano di Assetto Idrogeologico) of Calabria Region, published in 2006 and distributed by the Regional River Basin Authority. Inside the investigated area, a total of 4,102 landslides are mapped, 861 (21%) of which are classified as active, 3,220 (78%) as dormant and 21 (1%) as stabilized (the reference year is 2006). Landslides cover an area of 325 km 2 , corresponding to 7.3% of the whole territory (Fig. 1), and the main landslide typologies are represented by rotational slides and flows. The inventory of the PAI can be integrated also with the information from the IFFI (Inventario dei Fenomeni Franosi in Italia, Landslide Inventory in Italy) inventory, a national landslide database published in 2007. Both these sources of information (PAI and IFFI) are based on aerial photointerpretation, field surveys and collection of local databases mapped on a reference scale of 1:10,000.