When stresses yield a critical value, rock breaks and generate pathways for fluid migration. Thus, the contemporary undisturbed stress state is a key parameter for assessing the stability of deep geological repositories. In this workshop you can ask everything you always wanted to know about stress (but were afraid to ask), and this is divided into three parts. 1) How do we formally describe the stress field? 2) How do we to actually measure stress? 3) How do we go from points to 3D description?

The subsurface is subject to constant stress. With increasing depth, more rock overlies an area, thereby increasing the stress. There is also constant stress from the sides. Knowledge of this stress is fundamental to build lasting and safe underground structures. Very few data on the stress state are available; thus, computer models are used to predict this parameter. We present a method to improve the quality of the computer models, even if no direct data on the stress state are available.

Numerical methods can be used to estimate the stress state in the Earth’s upper crust. Measured stress data are needed for model calibration. High-quality stress data are available for the calibration of models for possible radioactive waste repositories in Switzerland. A best-fit model predicts the stress state for each point within the model volume. In this study, variable rock properties are used to predict the potential stress variations due to inhomogeneous rock properties.

Stress data predicted by a geomechanical–numerical model are mapped onto 3D fault geometries. Then the slip tendency of these faults is calculated as a measure of their reactivation potential. Characteristics of the faults and the state of stress are identified that lead to a high fault reactivation potential. An overall high reactivation potential is observed in the Upper Rhine Graben area, whereas the reactivation potential is quite low in the Molasse Basin.

In numerical geomechanical models, an initial stress state is established before displacement boundary conditions are applied in order to match calibration data. We present generic models to show that the choice of initial stress and boundary conditions affects the final state of stress in areas of the model domain where no stress data for calibration are available. These deviations are largest in the vicinity of lithological interfaces, and they can be reduced if more stress data exist.

The recent crustal stress state is a crucial parameter in the search for a high-level nuclear waste repository. We present results of a 3D geomechanical numerical model that improves the state of knowledge by providing a continuum-mechanics-based prediction of the recent crustal stress field in Germany. The model results can be used, for example, for the calculation of fracture potential, for slip tendency analyses or as boundary conditions for smaller local models.

In this study, we investigate the evolution of fault reactivation potential in the greater Ruhr region (Germany) in respect to a future utilization of deep geothermal resources. We use analytical and numerical approaches to understand the initial stress conditions on faults as well as their evolution in space and time during geothermal fluid production. Using results from our analyses, we can localize areas more favorable for geothermal energy use based on fault reactivation potential.

The authors assemble an in situ stress magnitude and orientation database based on 429 hydrofracturing tests that were carried out in six coal mines and two coal bed methane boreholes between 1986 and 1995 within the greater Ruhr region (Germany). Our study summarises the results of the extensive in situ stress test campaign and assigns quality to each data record using the established quality ranking schemes of the World Stress Map project.

Reactivation of tectonic faults can lead to earthquakes and jeopardize underground operations. The reactivation potential is linked to fault properties and the tectonic stress field. We create 3D geometries for major faults in Germany and use stress data from a 3D geomechanical–numerical model to calculate their reactivation potential and compare it to seismic events. The reactivation potential in general is highest for NNE–SSW- and NW–SE-striking faults and strongly depends on the fault dip.

The Earth's crust is subject to constant stress which is manifested by earthquakes at plate boundaries. This stress is not only at plate boundaries but everywhere in the crust. A profound knowledge of the magnitude and orientation of the stress is important to select and build a safe deep geological repository for nuclear waste. We demonstrate how to build computer models of the stress state and show how to deal with the associated uncertainties.

Knowledge of the crustal stress state is important for the assessment of subsurface stability. In particular, stress magnitudes are essential for the calibration of geomechanical models that estimate a continuous description of the 3-D stress field from pointwise and incomplete stress data. We present the first comprehensive and open-access stress magnitude database for Germany, consisting of 568 data records. We introduce a quality ranking scheme for stress magnitude data for the first time.

Knowledge about the stress state in the upper crust is of great importance for many economic and scientific questions. However, our knowledge in Germany is limited since available datasets only provide pointwise, incomplete and heterogeneous information. We present the first 3D geomechanical model that provides a continuous description of the contemporary crustal stress state for Germany. The model is calibrated by the orientation of the maximum horizontal stress and stress magnitudes.

The influence and interaction of elastic material properties (Young's modulus, Poisson's ratio), density and low-friction faults on the resulting far-field stress pattern in the Earth's crust is tested with generic models. A Young's modulus contrast can lead to a significant stress rotation. Discontinuities with low friction in homogeneous models change the stress pattern only slightly, away from the fault. In addition, active discontinuities are able to compensate stress rotation.

The knowledge of physical properties of quartz as an abundant rock-forming mineral in the Earth’s crust allows for a better understanding of its dynamic processes. The thermal transport properties of single-crystal quartz are studied between –120 °C and 800 °C using a laser flash method. First, low-temperature data as well as the role of the low-to-high quartz phase transition (e.g. a transition-related non-ballistic radiative transfer) and size effects on thermal diffusivity are discussed.

Based on geophysical data integration and 3-D gravity modeling, we show that significant density heterogeneities are expressed as two large high-density bodies in the crust below the Sea of Marmara. The location of these bodies correlates spatially with the bends of the main Marmara fault, indicating that rheological contrasts in the crust may influence the fault kinematics. Our findings may have implications for seismic hazard and risk assessments in the Marmara region.

Subsurface engineering relies on sparsely distributed data points of the stress state of the earth's crust. 3D geomechanical--numerical modelling is applied to estimate the stress state in the entire volume of a large area. We present a multi-stage approach of differently sized models which provide the stress state in an area of interest derived from few and widely scattered data records. Furthermore we demonstrate the changes in reliability of the model depending on different input parameters.

A numerical model integrating the structure and mechanical properties of a sedimentary sequence in the Alpine foreland is presented to show that topography, tectonic faults and, most of all, spatialy variable rock properties affect the state of stress at depth. The tectonic forces acting on the sequence are primarily taken up by the stiff rock units leaving the weaker units in a stress shadow.