Mount Etna dense array local earthquake P and S tomography and implications for volcanic plumbing

Inversion for the three-dimensional velocity structure of Mount Etna is performed with a data set of arrival times of P and S waves of local earthquakes from temporary dense arrays of three-component seismographs. A high-V-p body revealed by the original tomography without nearby stations is confirmed, and its image is sharpened using new velocity constraints provided by refraction data. Synthetic tests of V-p and V-p/V-s and comparison with an independent artificial source tomography with a fundamentally different geometry consistently calibrate the significance threshold of the resolution indicators. The trustworthy part of the image shows a high-V-p body centered under the southern part of Valle del Bove above the 6 km below sea level deep basement, which extends towards sea level and may be rooted in or through the crust. It has a large contrast of over 1 km/s with the surrounding sediments and sharp lateral limits and can thus be regarded as made of intrusive material of magmatic origin. The massive high-V-p body is heterogeneous in V-p/V-s. The regions inside it where V-s is relatively low can then be suspected of containing a proportion of melt or be fractured and act as pressure links or transport zones. Such features may be structurally linked and appear to be activated in eruptive phenomena. By taking into account the heterogeneities in structure and physical state retrieved by seismic tomography a succession of seismic events, deformational episodes, and geochemical variation in lavas can be discussed with respect to the well-observed eruptions.