Anisotropic Seismic Imaging of Mount Etna: Interplay Between Tectonics and Magma Ascent

Understanding the crustal structure and magma migration pathways beneath Mt. Etna (Italy) is crucial for volcanic hazard assessment. While isotropic seismic models successfully image major velocity anomalies beneath the volcano, they often neglect the significant seismic anisotropy generated by aligned fractures, fault systems, and magmatic bodies, potentially biasing interpretations of the volcanic plumbing system. This work presents the first comprehensive 3D P-wave anisotropic tomography of Mt. Etna, obtained from the inversion of local earthquake P-wave travel times assuming a transversely isotropic medium with an arbitrarily oriented symmetry axis. By simultaneously recovering isotropic velocities and three anisotropic parameters (magnitude, azimuth, and dip), the inversion allows for a more physically consistent imaging of the crustal volume beneath Mt. Etna. The model reveals a high-velocity complex in the central-southern sector of the volcano, characterized by a distinctive anisotropic signature with slow axes arranged in a near-circular pattern. This configuration is interpreted as a system of radial fractures and dykes associated with the emplacement of solidified magmatic bodies. At greater depths, a high-velocity volume deepening toward the northwest corresponds to the Hyblean foreland crustal units, which confine a low-velocity anomaly interpreted as magmatic fluids stored within the crust. A major tectonic discontinuity within these units appears to act as a preferential pathway for magma ascent from depth to the surface. By explicitly accounting for crustal anisotropy, this study provides new insights into the structural conditions leading to the emplacement of Mt. Etna, highlighting the interplay between regional tectonics, local stress fields, and magma ascent processes. More broadly, the results underscore the potential of seismic imaging that accounts for anisotropy to investigate the internal architecture of volcanic systems and, from a monitoring perspective, to track the evolution of stress fields and magma migration within the crust.