THE RECENT CRUSTAL STRESS-FIELD IN CENTRAL-EUROPE - TRAJECTORIES AND FINITE-ELEMENT MODELING

The recent crustal stress field of Central Europe and especially of the adjoining areas to the east is presented in terms of the directions of maximum horizontal stress (S(Hmax)). The analysis is based on fault plane solutions, in situ stress measurements, geologic fault slip determinations, and repeated precise geodetic triangulations. A bending of the direction of S(Hmax) from the well-known NW-SE direction in the western part of the study area to directions of NE-SW to E-W in the eastern part is shown. First results on the recent crustal stress field of the study area were presented by Grunthal and Stromeyer (1986), who substantiated this tendency of bending in the central and eastern parts of the study area by few observations only. Therefore one aim of this paper was to compile observations on the areas with few data points. Generally, these additional data confirm the previously established pattern; in some areas, especially in the Pannonian basin, the stress features became more complicated compared with those solely based on a few data points. The second part of the paper presents steady state elastic finite element model calculations to provide some possible explanations of the observed stress orientations as a result of plate driving forces. Simulation of the North Atlantic seafloor spreading and the northward directed motion of the African plate by appropriate boundary loads produces a pattern of S(Hmax) directions for the western part of the Eurasian plate which is compatible with the broad-scale observed stress directions. Subregional anomalies such as the fanlike stress pattern perpendicular to the arc of the Western Alps or the radial directions around the Pannonian basin can be explained only when additional stress producing features are introduced overmodulating the regional field. Rigorous introduction of physically constrained model parameters for all these features was not feasible to date. Therefore the preliminary empirical model calculations presented in this paper are attempts to discuss which features have the most influence on the stress field. They are, in a regional scale, the North Atlantic seafloor spreading, the northward motion of the African and the Arabian plate, and obviously, subregionally, increased stiffness of the Apulian promontary as well as of the Bohemian massif.