The analysis of slip tendency of major tectonic faults in Germany

Seismic hazard during subsurface operations is often related to the reactivation of pre-existing tectonic faults. The analysis of the slip tendency, i.e., the ratio of shear to normal stress acting on the fault plane, allows an assessment of the reactivation potential of faults. We use the total stresses that result from a large-scale 3D geomechanical–numerical model of Germany and adjacent areas to calculate the slip tendency for three 3D fault geometry sets with increasing complexity. This allows us to draw general conclusions about the influence of the fault geometry on the reactivation potential. In general, the fault reactivation potential is higher in Germany for faults that strike NW–SE and NNE–SSW. Due to the prevailing normal stress regime in the geomechanical–numerical model results, faults dipping at an angle of about 60∘ generally show higher slip tendencies in comparison to steeper or shallower dipping faults. Faults implemented with a straight geometry show higher slip tendencies than those represented with a more complex, uneven geometry. Pore pressure has been assumed to be hydrostatic and has been shown to have a major influence on the calculated slip tendencies. Compared to slip tendency values calculated without pore pressure, the consideration of pore pressure leads to an increase in slip tendency of up to 50 %. The qualitative comparison of the slip tendency with the occurrence of seismic events with moment magnitudes M$_w$>3.5 shows areas with an overall good spatial correlation between elevated slip tendencies and seismic activity but also highlights areas where more detailed and diverse fault sets would be beneficial

The crustal stress field of Germany: a refined prediction

Information about the absolute stress state in the upper crust plays a crucial role in the planning and execution of, e.g., directional drilling, stimulation and exploitation of geothermal and hydrocarbon reservoirs. Since many of these applications are related to sediments, we present a refined geomechanical–numerical model for Germany with focus on sedimentary basins, able to predict the complete 3D stress tensor. The lateral resolution of the model is 2.5 km, the vertical resolution about 250 m. Our model contains 22 units with focus on the sedimentary layers parameterized with individual rock properties. The model results show an overall good fit with magnitude data of the minimum (S$_{hmin}$) and maximum horizontal stress (SS$_{Hmax}$) that are used for the model calibration. The mean of the absolute stress differences between these calibration data and the model results is 4.6 MPa for Shmin and 6.4 MPa for SS$_{Hmax}$. In addition, our predicted stress field shows good agreement to several supplementary in-situ data from the North German Basin, the Upper Rhine Graben and the Molasse Basin