Abstract
Forward logistic regression and conditional analysis have been compared to assess landslide susceptibility across the whole territory of the Sicilian region (about 25,000 km2) using previously existing data and a nested tiered approach. These approaches were aimed at singling out a statistical correlation between the spatial distribution of landslides that have affected the Sicilian region in the past, and a set of controlling factors: outcropping lithology, rainfall, landform classification, soil use, and steepness. The landslide inventory used the proposal of building the models like the official one obtained in the PAI (hydro geologic asset plan) project, amounting to more than 33,000 events. The 11 types featured in PAI were grouped into 4 macro-typologies, depending on the inherent conditions believed to generate various kinds of failures and their kinematic evolution. The study has confirmed that it is possible to carry out a regional landslide susceptibility assessment based solely on existing data (i.e., factor maps and the landslide archive), saving a considerable amount of time and money. For scarp landslides, where the selected factors (steepness, landform classification, and lithology) are more discriminate, models show excellent performance: areas under receiver operating characteristic (ROC) (AUCs) average > 0.9, while hillslope landslide results are highly satisfactory (average AUCs of about 0.8). The stochastic approach makes it possible to classify the Sicilian territory depending on its propensity to landslides in order to identify those municipalities which are most susceptible at this level of study, and are potentially worthy of more specific studies, as required by European-level protocols.
Highlights
One of the most obvious effects of rapid territorial expansion in recent decades is the growing impact that natural disasters have on man and his activities
The geological setting of Sicily (Figure 1) consists of three main structural elements [16,17]: a range sector, running along the northern strip of the island, from the Peloritan Peaks to the Aegadian Islands, where Triassic to Mesozoic structural–stratigraphic units, mainly characterized by carbonate to clayey formations, tectonically overlap; a northwest-dipping foredeep area lying in the mid-southern area of the Sicilian territory, consisting of Plio-Pleistocene pelagic marly limestones, silty mudstones, and sandy clays overlying Messinian evaporites separated by the Sikan Peaks; the Hyblean Plateau located in southeastern Sicily, made up of a Triassic-Liassic platform and scarp-basin carbonates overlaid by Jurassic-Eocene pelagic carbonates and Tertiary open-shelf clastic deposits; southern and central Sicily feature Cretaceous-Lower Pleistocene clastic-terrigenous deposits and Messinian evaporites [18]
Landslides are directly connected to the many environmental condition types, mainly depending on slope morphology and other intrinsic characteristics, while the activation of new landslides depends on trigger factors, such as intensive rainfall or earthquakes [58,59,60]
Summary
One of the most obvious effects of rapid territorial expansion in recent decades is the growing impact that natural disasters have on man and his activities. The TIER approach is strictly dependent on the quality of the available data in landslide inventories and on thematic maps, required for the whole European territory This protocol consists of three nested levels (TIER1, TIER2, and TIER3) with a gradually increasing degree of resolution for the predictive models [10,11,12,13]. Joint Research Centre (JRC research group) are those based on expert-driven approaches such as conditional analysis, heuristics, and/or weighted factors In this piece of research, we have had the opportunity to verify and compare the use of the binary logistic regression (BLR) statistical technique on extensive areas, in the range of tens of thousands of square kilometers, contrary to suggestions by European Commission experts (Tier-based approach). Once the robustness of the scientific guidelines testing has been tested, the skills and the experience acquired may be used as a basis for the drafting of a Sicilian municipality susceptibility map, a useful tool for the policy-makers dealing with land management
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