Valutazione della pericolosità da caduta massi tramite un approccio integrato statistico e deterministico

In Val di Fassa (Dolomites, Eastern Italian Alps) rockfalls constitute the most relevant gravity-induced natural disaster threatening both the inhabitants of the valley and the thousands of tourists who populate the area in summer and winter times.To assess rockfall hazard, we developed an integrated statistical and physically-based approach aimed at predicting both the onset susceptibility and the reach probability of rockfalls. Through field checks and multi-temporal aerial photo-interpretation, we prepared a detailed inventory of both rockfall source areas and associated scree slope deposits. Grid-cells pertaining to the source area polygons were classified as active and inactive using an innovative technique based on GIS tools and a 3D rockfall simulation code (HY-STONE). The latter allows for linking each source grid-cell with scree slope deposit polygons by calculating the trajectory of each simulated launch of blocks. By means of discriminant analysis, we then identified the mix of environmental characteristics that better discriminate grid-cells with low and high rockfall susceptibility. Among the variables, the structural setting, land-use, and morphology resulted to be the most important factors leading to rockfall initiation. We developed 3D simulation models of the rockfall runout distance, intensity and frequency, assigning an either fixed or variable onset susceptibility; the latter derived from the discriminant model group (active/inactive) membership probabilities. The comparison of these models indicates that the variable onset susceptibility model appears the most realistic one.