Figure 10

Evolution of seismicity in a radius of 100 m around the boreholes during stimulation and SCCL. The upper part of the diagrams show the stimulation pressure and below, the time-evolution of induced seismicity is shown versus depth. The lower part of the diagrams shows the SCCL for the respective depth intervals. Different sections are marked by numbers and colors indicating the pressure steps of injection. With increasing stimulation pressure, seismicity migrates downwards for (a) GPK1 and upwards for (b) GPK3. The steps might be caused by clay-rich intervals, which rather promote creep than seismic shearing. After each pressure increase, seismicity begins at depths, where the clay-content is low until the pressure front reaches a clay-rich interval. This interval is overcome during the next pressure increase, and seismicity starts just after the clay-rich zone migrating towards the next clay-rich zone, and so on. From step 5 on, we assume that the pressure front migrated too far away from the borehole so that a correlation with the (two-dimensional) SCCL is not possible any more.