Correlation between tectonic CO₂ Earth degassing and seismicity is revealed by a 10-year record in the Apennines,...

Deep CO₂ emissions characterize many nonvolcanic, seismically active regions worldwide, and the involvement of deep CO₂ in the earthquake cycle is now generally recognized. However, no long-time records of such emissions have been published, and the temporal relations between earthquake occurrence and tectonic CO₂ release remain enigmatic. Here, we report a 10-year record (2009-2018) of tectonic CO₂ flux in the Apennines (Italy) during intense seismicity. The gas emission correlates with the evolution of the seismic sequences: Peaks in the deep CO₂ flux are observed in periods of high seismicity and decays as the energy and number of earthquakes decrease. We propose that the evolution of seismicity is modulated by the ascent of CO₂ accumulated in crustal reservoirs and originating from the melting of subducted carbonates. This large-scale, continuous process of CO₂ production favors the formation of overpressurized CO₂-rich reservoirs potentially able to trigger earthquakes at crustal depth.