Contemporary state of stress in a stable plate interior (northern Poland): The integration of satellite geodesy, borehole and seismological data

Abstract

In our study we examined the possibility of using strain rate data, determined from geodetic satellite measurements for estimations of magnitude of contemporary stress in a relatively stable area of northern Poland, comprised of fragments of the East European Craton, the Teisseyre-Tornquist Tectonic Zone and the Palaeozoic Platform. The strain rates and their principal directions were determined from 63 GNSS stations lacking special stabilization. The method for filtrating the unstable stations allowed us to eliminate half of these stations from the final strain rate calculations that included data averaging in a correlation radius of 150 km. A comparison of the horizontal strain directions determined by geodetic methods with the directions of contemporary stress based on borehole data (four of which were determined in this study) showed a high degree of convergence. Also the trends of strain rate variations showed consistency with integrated lithospheric strength of main tectonic units. The strain rates obtained are consistent with those published for the adjacent areas. Stress magnitudes were estimated by calibrating the timing of elastic strain accumulation by earthquakes in the Sambia Peninsula (Kaliningrad Oblast) and assuming a transient state of elastic strain on the craton. Our results indicate that the crystalline upper crust in the analysed part of the craton is in the strike-slip faulting stress regime prevailing over the normal faulting stress regime. The present state of an elastic strain has been accumulated over the last few million years causing stress being far from the critical state in the Mohr-Coulomb frictional criteria, except of the seismically active Sambia Peninsula.