Three dimensional gravimetric and geodynamic modelings of the region Vogtland/NW-Bohemia

The Vogtland/NW-Bohemia region is characterized seismological by the frequent occurrence of swarm earthquakes, which result probably from the physical interactions of fluids, the stress field and the geometry of the geological units. A high resolution three dimensional (3D) gravimetric model of the region was developed to yield information about the geological structure of the earth's crust and to investigate the mechanism of the swarm earthquakes with regard to tectonic fault zones, a magmatic system or an upwelling mantle at the crust-mantle boundary. A new Bouguer map is presented as requirement of the 3D gravimetric modeling. The anomalies of the Bouguer map are interpreted and correlated with geological units. It shows, that the epicentral zone is characterized by a strong gravity gradient. The 3D gravimetric model covers an area of 143.2 km times 165.2 km. It extends from the surface down to a depth of 35 km. Different boundary conditions, like results of seismic surveying and geological and tectonical information, are included into the model to reduce unavoidable ambiguity. The anomalies calculated from the final model fit well the measured anomalies. With regard to the swarm earthquakes in the studied area the existence of an upwelling mantle or a magmatic system is investigated. A 3D elastic modeling was carried out to verify the increased significance of the geometrical characteristics. The intension of the geodynamic modeling is to estimate the stress accumulation due to the tectonic process to get information about a postulated correlation between the stress field and geometrical characteristics with regard to the swarm earthquakes. The results focus on the importance of the granites, but additional physical processes have to take place to generate the swarm earthquakes.