Correlation between tectonic CO 2 Earth degassing and seismicity is revealed by a 10-year record in the Apennines, Italy

Deep CO emissions characterize many nonvolcanic, seismically active regions worldwide, and the involvement of deep CO 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 CO release remain enigmatic. Here, we report a 10-year record (2009-2018) of tectonic CO flux in the Apennines (Italy) during intense seismicity. The gas emission correlates with the evolution of the seismic sequences: Peaks in the deep CO 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 CO accumulated in crustal reservoirs and originating from the melting of subducted carbonates. This large-scale, continuous process of CO production favors the formation of overpressurized CO-rich reservoirs potentially able to trigger earthquakes at crustal depth.