The analysis of slip tendency of major tectonic faults in Germany

Abstract. 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 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 as hydrostatic and has 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 of 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 an overall good spatial correlation between areas of elevated slip tendencies and seismic activity for one of the investigated fault sets.