SpannEnD 2.0 – Improved present-day stress prediction of Germany by a new 3D geomechanical-numerical model

A robust prediction of the present-day stress state is of great importance for the safe usage of the subsurface, e.g., for borehole stability, mitigation of induced seismicity or the search and long-term safety of a high-level nuclear waste deposit. However, the state of knowledge concerning the stress state in Germany is limited as only unevenly distributed stress measurements are available. Two 3D geomechanical-numerical models created during the SpannEnD project (2018-2022) have improved this level of knowledge. Such geomechanical-numerical models - calibrated on available stress magnitudes - enable a continuum-mechanics based prediction of the present-day stress state. In the course of the follow-up project SpannEnD 2.0, a new, significantly improved model provides new insights into the stress state of Germany.   The new 3D geomechanical-numerical model combines information of 25 geological models and comprehensive additional data. The final geomechanical-numerical model comprises 52 geological units parametrized with individual mechanical properties (Young’ s modulus and Poisson’ s ratio) and densities. Linear elasticity is assumed and the finite element method (FEM) is used to solve the equilibrium of forces. Overall, the model contains ~10 million hexahedral elements providing a lateral resolution of 4 x 4 km2 and a vertical resolution of 45 m in the uppermost 5 km. A significantly enhanced stress magnitude database has been used for model calibration on magnitudes of the minimum (Shmin) and maximum horizontal stresses (SHmax). The model results show an overall good fit with these stress magnitudes indicated by a mean of the absolute stress differences of ~5 MPa for Shmin and SHmax.  Furthermore, our results agree well with additional data sets not used for calibration, e.g., an absolute mean deviation of the orientation of SHmax with regard to World Stress Map data of ~10° .