Source Mechanism of Seismicity Generated by one of the Last Active Coal Mines in Germany before its Closure
Abstract
Over the last 100 years, mining activity has been related to multiple induced seismic events that could be related to longwall caving at depth. In the Ruhr area in north-western Germany, coal mining activity has produced 41 M ≧ 2 events in the last two years alone. The planned cessation of coal mining activity at the end of 2018 could be accompanied by perturbation of the stress state on faults in close proximity to the mine due to, for example, the rise of the groundwater table as a consequence of a reduction in groundwater pumping. Quantifying the rates and source properties of ongoing seismicity is therefore necessary to constrain the mechanisms responsible for producing M ≧ 2 events, and for quantifying potential changes in seismicity post mining closure, and ultimately, for seismic hazard analysis.
Here, we focus on the seismicity generated by one of the remaining active mines in North-Rhine Westphalia (Germany): the Prosper-Haniel mine close to Bottrop city, with at least 9 M ≧ 2.5 events since the beginning of 2016. Our specific objectives include relating the timing and location of earthquakes with mining activity, and estimating earthquake source parameters in order to assess similarity with tectonic events. We develop an enhanced earthquake catalog using a multi-station matched-filter (MMF) approach with four templates, where templates are chosen based on a clustering analysis of 9 M ≧ 2.5 events listed in the Ruhr-University Bochum Seismological Observatory catalog. We use the 10 closest stations to the mine, i.e., 30 channels for the MMF detection, and a detection threshold eight times the median absolute deviation. We find over 2000 detections that are temporally clustered as foreshocks of templates, with templates exhibiting non-vigorous aftershock activity. Initial locations and relative relocations of the MMF catalog suggest most events are located within the top 3 km in depth. To investigate the mechanisms of the mining induced events, we use spatial correlations with reported longwall locations, moment tensor inversions, and estimate stress drop values using single spectra and spectral ratio methods.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.S21A..08P
- Keywords:
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- 7209 Earthquake dynamics;
- SEISMOLOGYDE: 7223 Earthquake interaction;
- forecasting;
- and prediction;
- SEISMOLOGYDE: 7230 Seismicity and tectonics;
- SEISMOLOGYDE: 8168 Stresses: general;
- TECTONOPHYSICS