A Semi-quantitative Approach to Assess the Propensity of Rockfall Source Areas to Instability Based on the Susceptibility Index to Failure (SIF): the Case Study of Capo Calavà (Italy)

This paper develops a practical semi-quantitative methodology to assess the probability of failure of unstable rock blocks for different environments (mountain and coastal-marine) and scales of interest (small and medium-large scales). According to the presence and intensity of several causative factors, a rockfall Susceptibility Index to Failure (SIF) can be defined and assigned to each rockfall source point so as to generate weighted frequency runout maps and, therefore, obtain more reliable rockfall hazard and risk maps. A novel approach, implemented in a Matlab routine, is also proposed to determine the release activity of different rockfall source areas, with reference to specific elements at risk. Such information makes it possible to identify the most efficient locations for the installation of risk monitoring or mitigation systems. The proposed methods are applied to a case study in the northern coast of Sicily, Italy, where a susceptibility analysis is carried out in the QGIS environment by means of the QPROTO plugin (QGIS Predictive ROckfall TOol).