FloodRisk – Induced seismicity by mine flooding – Observation, characterisation and relation to mine water rise in the eastern Ruhr area (Germany)

Abstract

As part of the FloodRisk project, the influence of rising mine water in abandoned coal mines on induced seismic-ity is investigated. The Seismological Observatory of the Ruhr University Bochum operates a monitoring network for the whole Ruhr area (North Rhine-Westphalia, Germany) since 1983. The local scale FloodRisk network was installed in the eastern part of the Ruhr area in 2020. The continuous monitoring opens up the opportunity for a long-term study of seismic-ity in combination with water levels related to mining in the region. The resulting database for the eastern Ruhr area includes over 13,000 induced earthquakes in a period of 26 years during active mining, very few events in the postmining phase be-fore the onset of flooding and more than 1,700 events in the first two and a half years of flooding. The seismological database is supplemented by the mine water levels, which are regularly measured at various measuring points distributed over the study dewatering area “Haus Aden” and made available by Ruhrkohle Aktiengesellschaft (RAG). Seismic activity was highest in the phase of active mining and concentrated in the vicinity of the mining areas. After the end of mining, only very low seismicity was detected. With the start of flooding, significantly more events were registered again. The rise curve of the mine water level and the temporal and spatial distribution of the seismicity are observed and analysed. Five temporal flooding phases are identified in which the correlated seismicity shows different distribution patterns. Phases in which the levels of individual sections of the mine merge in flooding show particularly high seismicity. A strong spatial clustering of well-localised events occurs below the deepest flooded levels of the mine. Several mechanisms that alter the stress in active mining and flooded mines and induce seismic events are known from previous studies. To apply this to our study, particular attention is given to the spatial distribution of seismicity in relation to known geologic and mining struc-tures. In the flooding phase, most of the seismicity is localised in the area below the flooded drifts.