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Low signal-to-noise event detection based on waveform stacking and cross-correlation: application to a stimulation experiment |
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| Authors: | Katrin Plenkers Joachim R R Ritter Marion Schindler |
| Institution: | 1. Karlsruhe Institute of Technology, Geophysical Institute, Hertzstr. 16, 76187, Karlsruhe, Germany 2. Swiss Seismological Survey (SED), ETH Zurich, Sonneggstr. 5, CH-8092, Zurich, Switzerland 3. BESTEC GmbH, Oskar-von-Miller-Str. 2, 76829, Landau, Germany |
| Abstract: | We study the microseismicity (M L ?<?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?<?M L ?<?~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 M L ?~?0.7 is not found in the region of Landau by our analysis. |
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