Аннотация
We study the microseismicity (ML < 2) in the region of Landau, SW
Germany. Here, due to thick sediments (\~3 km) and high cultural
seismic noise, the signal-to-noise ratio is in general very low for
microearthquakes. To gain new insights into the occurrence of very
small seismic events, we apply a three-step detection approach and
are able to identify 207 microseismic events (-1 < ML < \~1) with
signal-to-noise ratios smaller than 3. Recordings from a temporary
broadband network are used with station distances of approximately
10 km. First, we apply a short-term to long-term average detection
algorithm for data reduction. The detection algorithm is affected
severely by transient noise signals. Therefore, the most promising
detections, selected by coinciding triggers and high-amplitude measures,
are reviewed manually. Thirteen seismic events are identified in
this way. Finally, we conduct a cross-correlation analysis. As master
template, we use the stacked waveforms of five manually detected
seismic events with a repeating waveform. This search reveals additional
194 events with a cross-correlation coefficient exceeding 0.65 which
ensures a stable identification. Our analysis shows that the repeating
events occurred during the stimulation of a geothermal reservoir
within a source region of only about 0.5 km3. Natural background
seismicity exceeding our detection level of ML \~ 0.7 is not found
in the region of Landau by our analysis.
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