Origin of earthquake swarms in the western Bohemian Massif: Is the mantle CO2 degassing, followed by the Cheb Basin subsidence, an essential driving force?

• We propose a new model of origin of earthquake swarms in the Western Bohemian Massif.
• CO2 degassing of the metasomatized mantle may cause the Cheb Basin subsidence.
• The subsidence and the regional stress field may account for the seismicity.
• Swarms concentrate at a boundary between two lithospheric segments of different age.
• The largest earthquake energy has been released at a granite–orthogneiss contact.

We propose a new model of the origin of earthquake swarms in West Bohemia/Vogtland (central Europe) by extensive CO2 degassing of carbonates in the metasomatized junction of three mantle domains. The associated volume change of the decarbonation reaction accounts for the continuing subsidence of the Cheb Basin adjacent to the major focal zone. The local stress perturbation created by the subsidence, in combination with the regional stress field, may account for the recurring swarm seismicity. The largest earthquake energy has been continuously released along a steep contact between orthogneisses of the uplifting Krušné Hory/Erzgebirge domain and granites of the subsiding Smrčiny/Fichtelgebirge domain, forming boundary between two lithospheric segments. The physical parameters of both lithologies, Poisson's ratio and bulk modulus, derived from the P- and S-wave velocities at different depths indicate that this high-friction suture might be able to accumulate deformation energy that is being released as periodically recurring seismic swarms. The proposed model represents an alternative to prevailing considerations suggesting that the earthquake swarms were triggered by pressurized fluids of mantle origin, whose sources are however separated from the earthquake foci.