Mantle flow dynamics and formation of the curved Calabrian subduction zone

The formation mechanism of curved subduction zones remains poorly understood. To address this issue, we conduct a joint inversion of P-wave travel-time data from local earthquakes and teleseismic events for 3-D isotropic and anisotropic velocity tomography of the curved Calabrian subduction zone. Our results show that in the central and northern Apennines, the Adriatic Sea plate subducts on both the eastern and western sides. The westward-dipping slab retreats eastward, compressing the mantle below the double-side subduction zone. This compression pushes the mantle material to flow through a slab window below Mt. Vesuvius toward the Tyrrhenian Sea, resulting in nearly east-west oriented seismic anisotropy. As the distance between the double-side slabs decreases, the slab retreat slows down, leading to a differential retreat rate along the Apennines-Sicily. This difference, combined with mantle flow around the southwestern edge of the Calabrian slab, contributes to the observed curvature of the Calabrian subduction zone. Our findings provide new insights into dynamics of the curved subduction zone, highlighting the complex interaction between the slab retreat and mantle flow.