The role of CO2 degassing in the seismogenic process of the Apennines, Italy

An accurate survey of old and new datasets allowed us to probe the nature and role of fluids in the seismogenic processes of the Apennines mountain range in Italy. Geodynamics, geophysical and geochemical observations highlight differences between the western and eastern domains of the Apennines, and the main characteristics of the transition zone, which spatially corresponds with the overlapping Tyrrhenian and Adriatic Mohos. Tomographic images exhibit a large hot asthenospheric mantle wedge that intrudes beneath the western side of the Apennines and disappears at the southern tip of the southern Apennines. This wedge modulates the thermal structure and rheology of the overlying crust as well as the melting of carbonate-rich sediments of the subducting Adriatic lithosphere. As a result, CO₂-rich fluids of mantle-origin have been recognized in association with the occurrence of destructive seismic sequences in the Apennines. The stretched western domain of the Apennines is characterized by a broad pattern of emissions from CO₂-rich fluids that vanishes beneath the axial belt of the chain, where fluids are instead trapped within crustal overpressurized reservoirs, favoring their involvement in the evolution of destructive seismic sequences in that region. In the Apennines, areas with high mantle He are associated with different degrees of metasomatism of the mantle wedge from north to south. Beneath the chain, the thickness and permeability of the crust control the formation of overpressurized fluid zones at depth and the seismicity is favored by extensional faults that act as high permeability pathways. This study strongly relies on the multidisciplinary analysis of different datasets (both existing and newly acquired) with the most advanced methodologies to stimulate the knowledge of the fluid-related mechanisms of earthquake preparation, nucleation and space-time evolution. Ongoing and future investigations will include the continuous and simultaneous geochemical and geophysical monitoring at the scale of the outcropping seismogenic faults to properly decipher the link between earthquake occurrence, surface rupture and fluid release.