Capable fault assessment in Seismic Microzonation of volcanic environments: fault behaviour classes and zone‑based mapping from the Mt. Etna (Italy) case study

The volcanic region of Mt. Etna (Sicily, Italy) presents a unique challenge for seismic hazard assessment due to the interplay between regional tectonics, flank instability, magmatic processes and shallow volcano‑tectonic dynamics. The area is frequently affected by shallow (H < 5 km), moderate‑magnitude earthquakes (Mmax ≈5.0) that generate extensive surface faulting, often disproportionate to their energy release. Standard national regulations for “Active and Capable Faults” (ACF), originally designed for tectonic environments, fail to address specific volcanic features such as “hidden” faults, aseismic creep, and diffuse fracturing fields. This paper presents the newly developed “Guidelines for the study of Active and Capable Faults in the Etna volcanic area” (GL_ACF_Etna, Version 2.1). We introduce a tailored classification system that distinguishes between Exposed and Buried ACFs, creeping faults and Active Fracturing Zones (AFZ). Furthermore, we define criteria for delimiting Respect Zones (RZ) and Susceptibility Zones (SZ) for Level 3 Seismic Microzonation (SM3). The proposed methodology integrates historical macroseismic data, high‑resolution geological mapping, geophysical investigation and multi‑temporal InSAR analysis to provide a robust tool for land‑use planning in one of Europe’s most active volcanic areas.