ALBERT

Description: The use of Remotely Piloted Aircraft Systems (RPASs) in geosciences is often aimed at the acquisition of an image sequence to produce digital models and orthophotographs of the topographic surface. The technology can be applied for rockfall hazard and risk assessment. To study rockfalls, an approach consists in the application of numerical models for the computation of rockfall trajectories. Data required for such models include accurate digital terrain models, location of the instability source areas, and the mechanical properties of the terrain. In this article, we present an analysis of the earthquake-triggered rockfall that occurred along the SP18 in Villanova di Accumoli (Lazio, central Italy) during the 24 August 2016 seismic sequence. A survey with a multicopter was carried out to obtain an accurate surface model of the terrain, the identification and characterization of the source areas and of other instable blocks in areas not accessible in the field. The investigated area extends for 6,500m2 and was covered by 161 photographs that were used to obtain an orthophoto with a ground resolution of 2.5cm, and a digital surface model with a ground resolution of 20cm×20cm, which was processed and fused with GNSS RTK data. We run the numerical model STONE, using the source areas mapped in the field and adopting a slope threshold to get a map showing the rockfall potential trajectories. Results showed that only the part of the road SP18 hit by the rockfall was exposed to further rockfall impacts. In particular, it was observed that 16% (i.e. 5,108) of the 31,800 simulated trajectories reached or crossed this tract of the road. Based on these data, limited protection measures were suggested. The combined use of RPAS data, fused with ground GPS points, an accurate geomorphological survey, and terrain static and dynamic parameters from the literature, allows fast, low-cost and replicable numerical modelling for emergency response and adoption of proper protection measures.