Crustal deformations in the epicentral area of the West Bohemia 2008 earthquake swarm in central Europe

In West Bohemia, central Europe, during October 2008 an earthquake swarm of 25,000 shocks with a maximum event of M L ∼ 3.7–3.8 occurred at depths of 7–11 km. In 2007, annual GPS campaigns were launched. During the co‐seismic phase , displacements of a few centimeters were detected at GPS sites. Maximum displacement was revealed at the KOPA site, which subsided by 167 mm. The epicentral area is covered by eluvium of 4–10 m thick, and is located in undulating pastures and well‐forested valleys where visible surface soil effects could not be observed. To test possible fault manifestations, rough geomorphologic, geoelectric, and geochemical surveys were performed. GPS and seismic data, with geologic materials, were used to build a forward model for surface displacements, crustal deformations, and shear and normal stress fields. The fields enabled us to better determine crustal deformations and stresses that appeared within the seismic cycle, during the pre‐ , co‐ , and post‐seismic phases. During the co‐seismic phase , modeled fault motions along N‐S faults located within the epicentral zone reached 0.6–1 mm/day. Possible structural block rotations were comprised of these motions. A dominant role for stress accumulation, release, and relaxation was assigned to the Mariánské Lázně fault zone and the Nový Kostel zone. Strain loads slowly, and when local PT conditions with an action of deep magmatic fluids reach instability, the strain is released and stress balancing occurs. The process leads to the reversible motions known for silent earthquakes. A forward crustal deformation model for West Bohemia is also presented within.