Investigating the role of stratigraphy in large-area physically-based analysis of December 1999 Cervinara shallow landslides

The paper describes a large-area analysis of the triggering zones of shallow landslides on a case of unsaturated layered volcanic air-fall (pyroclastic) soil deposits in Cervinara site (18 km²), Southern Italy. The physically-based model TRIGRS (Transient Rainfall Infiltration-Based Grid Regional Slope-Stability) is used, which is used with either saturated or unsaturated conditions and implemented in a GIS platform. In addition to using the TRIGRS model to simulate some recent landslides, a new simplified approach is also tested to take into account the actual layered soil stratigraphy. The consistency check of the model and of the input data is performed with reference to slope stable conditions before rainfall. The performances of the models are evaluated through the ROC curves and two other quantitative indexes taken from the literature referring to the slope failures caused by December 1999 rainstorm. Notwithstanding the simplifications and limitations of the present work, both unsaturated conditions and layered stratigraphy are outlined as key factors for the slope stability of shallow deposits of unsaturated coarse-grained soils subjected to short heavy rainfall.