Pressurized magma storage in radial dike network beneath Etna volcano evidenced with P-wave anisotropic imaging.

Investigating crustal stress beneath volcanoes is critical to understanding the dynamics of eruptions. To this end, seismology represents a powerful monitoring tool. The opening of fluid-filled fractures due to the interplay of different stress sources produces elastic anisotropy within the crust, affecting the propagation of seismic waves. Here we use probabilistic imaging for the inversion of P-wave travel times to map elastic anisotropy of the magmatic system beneath Mt. Etna (Italy). These images provide localized information about fracture orientations and stress below this active volcano. Comparing inferred stress with independent observations and geodynamic modeling, we show evidence of a pressurized magma storage in a radial dike network between 6 and 16 km depth under the volcano. The radial network of vertical dikes constitutes a system of oriented pathways for the upward migration of magma from the depths, leading to eruptive activity from the summit craters and lateral vents at Mount Etna.