Conclusions
We propose a structural model for the lithosphere-asthenosphere system of Italy and neighbouring areas by means of VS-depth distribution. The multidisciplinary approach is used to better constrain our model to the independent geological, geophysical and petrological information. The obtained picture of the lithosphere-asthenosphere system confirms the existence of some known features: the lithospheric roots in the western and central Alps, the extended LVZ beneath the Tyrrhenian Sea, steep subduction beneath Calabrian arc, low-angle subduction under the Dinarides.
New evidence reinforces the hypothesis of an asymmetric expansion process of the Tyrrhenian Sea, as the presence of the lithospheric “boudinage” extended along a NW-SE direction through the whole Tyrrhenian Sea, likely representing fragments of the Alpine-Betic collision dragged by the eastward migrating process of the Apennines subduction. Another feature enlightened is the easterly rising shallow low-velocity layer from about 140 km to about 30 km in the Tyrrhenian active part of the backarc basin.
Further proofs for undergoing subduction processes of the Adriatic lithosphere towards northeast beneath the Dinarides and toward the west beneath the Apennines, with significantly different dip angles, corroborate the existence of a global asymmetry between the eastward and westward subduction processes, induced by the eastward relative mantle flow.
The Tertiary to Present subduction processes in the Italian area occurring on a Mesozoic disrupted lithosphere can account for the relevant lateral anisotropies visible in the mantle.
The arc-shaped Ionian-Adriatic lithosphere supports a strong connection between Hellenic subduction and Ionian-Tyrrhenic subduction, possibly endorsing an upduction-subduction counterflow mechanism in the upper mantle.
A wide use of seismicity analysis, both from catalogues and moment tensor inversion by the INPAR method, represents a significant constraint to the model interpretation. INPAR allows the use of relatively short period waveforms, significantly improving the depth determination for shallow events, usually fixed by CMT and RCMT. The depth and the focal mechanism of a significant damaging event of Umbria-Marche sequence are drastically changed with respect to CMT and RCMT determinations, leading to a better comprehension of the local stress field.