Earthquake dynamics sustained by seismic CO2.

Seismic faults paradoxically combine high frictional strength, which promotes stress accumulation and should hinder slip, with large seismic displacements. Among proposed dynamic weakening mechanisms, shear heating is crucial because it triggers decarbonation and CO₂ production. In carbonate faults, this process generates transient CO₂ pressurization that can modulate rupture dynamics and promote supershear propagation, yet the amount and pressure of produced CO₂ remain poorly quantified. We investigate carbonate faults in the Apennines, Italy, a region affected by Mw≤7.1 earthquakes. Integrating nano-scale observations of fault surfaces with mineralogical and isotopic constraints, we develop a stoichiometric-thermodynamic model linking seismic decarbonation to Mw 5.9-6.5 earthquakes. Individual events can produce up to 12 tons of CO₂, generating quasi-lithostatic pressures ( ~ 196 MPa) under undrained confinement and supra-hydrostatic pressures (76-134 MPa) under drained conditions. Here, we conclude that seismic CO₂ pressurization can sustain dynamic slip and enhance the destructive potential of earthquakes in carbonate terrains.