Discovery of scattered subvolcanic complexes that feeded the volcanism in the area of Etna

In this work we present a new tomographic inversion of the velocity structure and hypocenter parameters at Mt. Etna, carried out by the larger seismic dataset never used than to the previous tomographies. The result of tomographic inversion, including the 3D distributions of P and S velocities, Vp/Vs ratio, and accurate source locations, has been obtained based on the integration of active seismic data (151.403 P-phases from 4.112 shots) acquired during the 2014 TOMO-ETNA experiment (EC-FP7 MED-SUV and EUROFLEET2 MED-SUV.ISES projects) and 10.955 selected local earthquakes data (218.473 P-phases and 39.073 S-phases), recorded by a total number of 262 stations of the INGV permanent seismic network and from the onland and OBS temporary network. For the inversion we used the tomoDDPS algorithm [Zhang et al., 2009] and the input velocity model previously obtained with the PARTOS code (Moreno et al. 2016), considering a total number of 1.580.343 P and 228.663 S differential times.

Based on our data selection and inversion strategy, we obtain a strongly improved 3-D high-resolution Vp, Vs and Vp/Vs models both onland and offshore the volcano, discovering for the first time, in the peripherical part of the edifice: i) on-land, the presence of two subvolcanic complexes in the south-eastern and southern flanks, west to Acicastello-Acitrezza and Paternò and Motta, respectively, where the Etna’s ancient volcanisms (500 to 110 ka) manifested and ii) the presence of a ca. N-S oriented high velocity anomaly (5.0-6.5 km/s) located offshore southeast of Etna area, suggesting a clear interplay between submarine volcanic manifestations and tectonic setting. This body extending from about the sea level to ca. 8 km b.s.l. confirms the observation of a large and intense magnetic positive anomaly (>700 nT) related to deep sources (Cavallaro et al., 2016), evidenced by the magnetic survey carried out during TOMO-ETNA.