FloodRisk: Observations of rising mine water level and micro seismicity in the eastern Ruhr area (Germany)

FloodRisk is an interdisciplinary project focusing on the effects of mine water level rise in abandoned coal mine regions in Germany. Such effects are heterogeneous ground uplift, stress changes due to the change in pore pressure and the reactivation of potential faults. One of the most directly measurable effects is the induced micro seismicity. In this study the relationship between mine water rise, fluid-induced stress changes and induced seismicity in the Haus Aden dewatering area in the eastern Ruhr area (Germany) will be investigated in more detail. For this purpose, we operate a network of short period seismic stations in the region of the former "Bergwerk Ost" colliery, which had the highest seismicity rate in the Ruhr area during active underground coal mining (closed 2010). Level of induced seismicity started again when pumps were shut down (mid 2019). We were able to detect and localise more than 1000 microseismic events in magnitude range between -0.7 and 2.6 Mlv. Many of these events are spatially clustered and some show quite high waveform similarity. This allows relative localisation and can increase the accuracy of the location. The depth location of the earthquakes, within the limits of localisation accuracy, agrees very well with the distribution of seismicity at the time of active mining. The measured temporal trend of the mine water level shows a strong correlation with the temporal evolution of the observed micro seismicity.