Earthquake clustering and structural modelling unravel volcano-tectonic complexity beneath Mount Etna.

Active volcanoes are dynamic systems whose internal structure is key to assessing associated hazards. This study investigates the deep architecture of Mount Etna by integrating seismic data with crustal tectonic models. We analyse ~ 15,000 earthquakes (2002-2021) using a density-based clustering algorithm to identify seismogenic structures and their kinematics. Seismic activity correlates with eruptive periods, indicating that both deep and shallow structures respond to magmatic pressure and stress transfer. The results unveil a complex fault network that plays a crucial role in flank instability and stress redistribution, revealing a subsurface structural framework that differs significantly from its surface expression. A key finding concerns the eastern flank, which does not behave as a coherent sliding block but rather exhibits a multilayered deformation pattern controlled by inherited faults and pressure from the magmatic feeding system. This highlights the interplay between magmatic, tectonic, and gravitational processes. The approach provides a refined framework for understanding Etna's dynamics and can be applied to other active volcanoes in complex tectonic settings.