3-D model reveals thermal decomposition as a potential driver of seismicity in the Apennines, Italy

Earthquakes in the Central Apennines of Italy generate extensive aftershock sequences, with high-pressure CO₂ often implicated as an important contributor to seismogenesis. Fluid pressure diffusion (through porous media) of mantle-derived high-pressure CO₂ trapped in reservoirs is assumed to drive these sequences, yet seismic evidence of diffusion fronts remains elusive. We show here that co-seismic thermal decomposition also imposes numerous additional and isolated high fluid pressure sources that diffuse to drive the aftershock sequences. Numerical simulations mimic the generation of thermally decomposed fluids and reproduce the 2009 L’Aquila M_w 6.3 and the 2016 Amatrice-Visso-Norcia M_w 6.5 earthquake sequences. We identify hydraulic barriers and a minimum magnitude (M_w > 4) for thermal decomposition, which generate significant aftershock sequences in carbonates. The implications of thermal decomposition in seismogenesis are far-reaching and can be applied to any system, such as within subduction zones.