Seismically induced rockfall modelling using a 3D integrated approach: Ischia Island (Italy) case study

Rockfalls pose a major hazard in seismically active mountainous areas, where steep slopes and complex topography amplify instability processes. This study presents an integrated workflow to evaluate earthquake-induced rockfalls by combining geostructural investigations, three-dimensional seismic site response analyses, and numerical simulations of block propagation. Field and UAV-based surveys were conducted on the western sector of Mt. Epomeo, Ischia Island (Italy), allowing the characterisation of the discontinuity sets and the definition of representative block volumes and shapes (5, 20, and 60 m3). Critical peak ground accelerations (ac) were analytically derived for each block type using probabilistic strength parameters. Three-dimensional finite element models reproduced local seismic amplification effects, producing spatial distributions of peak ground acceleration (PGA) under different scenarios. By comparing PGA with ac values, potential release areas were identified, and the initial velocity was computed. These parameters were used for rockfall trajectory simulations, considering different scenarios of rock shape and volume, as well as release conditions. The results highlighted the influence of block volume and shape on propagation, with larger volumes developing higher kinetic energies and longer runouts, affecting urbanised areas. The vegetation acted, in some cases, as a natural barrier, stopping approximately half of the simulated blocks. The proposed workflow demonstrates the potential of integrating site response modelling and rockfall simulations to quantify seismic-induced hazard in complex volcano-tectonic settings, providing a replicable methodology for similar multi-hazard environments.