Microseismicity in relation to the rise of the mine water level and the regional stress field in the eastern Ruhr area

Using data from permanent seismological stations of the Ruhr University and the temporal short-period FloodRisk network in the eastern Ruhr area, microseismicity in the area of the former coal mine “Bergwerk Ost” is observed. The database is supplemented by the levels of the mine water table, which are regularly measured and made available by Ruhrkohle AG (RAG) at various measuring points distributed over the study area. A special focus is on the relation of the microseismicity to the rising mine water level after the end of mining.

Since the beginning of the flooding, more than 2000 induced events in a magnitude range from -0.7 up to 2.6 MLv have been localised. The spatial distribution of hypocentres is divided into two areas, with few events in the central study area and over 95% of earthquakes in its eastern part. Many of these events are spatially clustered and some show quite high waveform similarity. This allows relative localisation to increase the accuracy of the location.

Comparing the old galleries, which today serve as the main underground waterways, with the localisations from the relative seismicity localisation, strong correlations can be seen. The measured temporal trend of the mine water level, after pumps were shut down in mid-2019, shows a strong correlation with the temporal evolution of the observed microseismicity.

In addition to investigating the spatial and temporal distribution of seismicity, fault plane solutions could be determined for larger seismic events. These are compared with the regional stress field derived from independent investigations.