3D crustal stress state of Western Central Europe according to a data-calibrated geomechanical model – first results

Abstract

Abstract. The contemporary stress state in the upper crust is of great interest for geotechnical applications and basic research likewise. However, our knowledge of the crustal stress field from the data perspective is limited. For Western Central Europe basically two datasets are available: Orientations of the maximum horizontal stress (SHmax) and the stress regime as part of the World Stress Map (WSM) database (Heidbach et al., 2018) as well as a complementary compilation of stress magnitude data of Germany and adjacent regions (Morawietz et al., 2020). However, these datasets only provide pointwise, incomplete and heterogeneous information of the 3D stress tensor. Here, we present a geomechanical-numerical model that provides a continuous description of the contemporary 3D crustal stress state on a regional scale for Western Central Europe. The model covers an area of about 1000 × 1250 km2 and extends to a depth of 100 km containing seven lithostratigraphic units, with specific material properties (density and elastic rock properties) and laterally varying thicknesses: A sedimentary unit, four different units of the upper crust, the lower crust and the lithospheric mantle. The model is calibrated by the two datasets to achieve a best-fit regarding the SHmax orientations and the minimum horizontal stress magnitudes (Shmin). The modelled orientations of SHmax are almost entirely within the uncertainties of the WSM data used and the Shmin magnitudes fit to various datasets well. Only the SHmax magnitudes show locally significant deviations, primarily indicating too low values in the lower part of the model. The model is open for further refinements regarding model geometry, e.g., additional layers with laterally varying material properties, and incorporation of future stress measurements. In addition, it can provide the initial stress state for local geomechanical models with a higher resolution.

Stress rotation – impact and interaction of rock stiffness and faults

“…First of all, only one single elastic material composition represents each of the Variscan units. The model did not reproduce the complex and uncertain vertical variability of the deeper structures (Franke et al, 1990;Aichroth et al, 1992;Blundell et al, 1992), as no deep wells are present there. Only refraction seismic profiles from the 1980s (DEKORP) and their interpretations are available (Meissner and Bortfeld, 1990).…”

“…However, the overall geometry seems reasonable, as the brittle domain or elastic thickness of the lithosphere (T e), which is a measure of the integrated stiffness of the lithosphere, is of the order of 30 km and more in central Europe (Tesauro et al, 2012). The Moho depth in Germany or central Europe is also about 30 km (Aichroth et al, 1992;Grad and Tiira, 2009). Jarosiński et al (2006) for example used a range of T e = 30-100 km for their model of central Europe.…”

“…The complex stress pattern in central-western Europe was a subject of several numerical investigations in recent decades (Grünthal and Stromeyer, 1986Gölke and Coblentz, 1996;Goes et al, 2000;Marotta et al, 2002;Kaiser et al, 2005;Jarosiński et al, 2006). Apart from a recent 3-D model (Ahlers et al, 2020), the previous models were limited to 2-D. These 2-D models were able to reproduce some of the observed stress patterns by considering variable lateral elastic material properties or discontinuities.…”