Earthquake-induced rockfall hazard zoning

A methodology for quantitative probabilistic hazard zonation for earthquake-induced rockfalls is presented and demonstrated in the area of Friuli (Eastern Italian Alps) affected by the 1976 Mw 6.5 earthquake. Four rockfall datasets have been prepared both from historical data analysis and field surveys. The methodology relies on a three-dimensional hazard vector, whose components include the rockfall kinetic energy, the fly height, and the annual frequency. The values of the first two components are calculated for each location along the slope using the 3D rockfall runout simulator Hy-STONE. The rockfall annual frequency is assessed by multiplying the annual onset frequency by the simulated transit frequency. The annual onset frequency is calculated through a procedure that combines the extent of unstable areas, calculated for 10 different seismic-hazard scenarios with different annual frequencies of occurrence, and the magnitude relative-frequency relationship of blocks as derived from the collected field data. For each annual frequency of occurrence, the unstable area is calculated as a function of morphometric and earthquake characteristics. A series of discriminant-analysis models, using the rockfall datasets and DEMs of different resolution (1 and 10 m), identified the controlling variables and verified the model robustness. In contrast with previously published relationships, we show that the slope curvature plays a relevant role in the computation of the unstable area. © 2014 Elsevier B.V. All rights reserved