Abstract
Abstract. We have used several flooding-induced microseismic events that occurred in an abandoned mining area to image geological structures close to the hypocentres in the vicinity of the mine. The events have been located using a migration-based localization approach. We used the recorded full waveforms of these localized microseismic events and have processed these passive source data as if they resulted from active sources at the known hypocentre location and origin time defined by the applied location approach. The imaging was then performed using a focusing 3D prestack depth migration approach for the secondary P-wave arrivals. The needed 3D migration velocity model was taken from a recent 3D active (controlled-source) seismic survey in that area. We observed several clear and pronounced reflectors in our obtained 3D seismic image cube, some of them related to a major fault zone in that area and some correlating well with information from the nearby mining activities. We compared our results to the 3D seismic image cube obtained directly from the 3D active seismic survey and have found new structures with our approach that were not known yet, probably because of their steep dips which the 3D active seismic survey had not illuminated. The location of the hypocentres at depth with respect to the illumination angles of those structures proved to be favourable in that case, and our 3D passive image complements the 3D active seismic image in an elegant way, thereby revealing new structures that cannot be imaged otherwise with surface seismic configurations alone.
Highlights
Active seismic surveying is widely used in academia or industry for various purposes, for example, hydrocarbon exploration, mineral prospecting, and geothermal reservoir characterization, or for more general studies of the Earth’s crust
passive seismic imaging (PSI) methods have their own requirements and limitations: an existing seismic monitoring network with a sufficiently large number of seismic stations is needed; the position and distribution of sources with respect to target structures cannot be arranged; the frequency of occurrence and the magnitude of events cannot be controlled; and events with larger magnitude occur on fault planes that act as sources which cannot be considered point sources anymore and may include the target structures – i.e. the energy source and the reflectors are physically not separated
In 2012, an active 3D seismic survey was conducted in the region covering an area of about 10 km × 13 km including the Schlema-Alberoda mining area in order to explore the potential of using pre-existing fault zones as hydraulic paths and natural heat exchanger within a geothermal energy production scenario (Hloušek et al, 2015; Lüschen et al, 2015)
Summary
Active (controlled-source) seismic surveying is widely used in academia or industry for various purposes, for example, hydrocarbon exploration, mineral prospecting, and geothermal reservoir characterization, or for more general studies of the Earth’s crust. In 2012, an active 3D seismic survey was conducted in the region covering an area of about 10 km × 13 km including the Schlema-Alberoda mining area in order to explore the potential of using pre-existing fault zones as hydraulic paths and natural heat exchanger within a geothermal energy production scenario (Hloušek et al, 2015; Lüschen et al, 2015). Through this survey, several structures were accurately imaged using state-of-the-art imaging techniques. The existing 3D seismic image obtained from the aforementioned active seismic survey gives us the unique possibility to compare the results from the passive seismic approach against it and to evaluate the reliability and accuracy of the final PSI results
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