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Using an ultra-high frequency seismic network, the researchers detected seismic events as small as Mw < −4, revealing a complex fracture network extending over 100 meters from the injection sites. The analysis shows significant variability in the affected rock volume, ranging from a few meters to over 150 meters, and identifies multiple reactivated fractures. Seismic events typically propagate upward along planes aligned with the stress field and pre-existing fractures. The results highlight the diversity in seismic behavior, which is not solely dependent on the injection protocol, and confirm that multi-stage stimulations with zonal isolation can create a large, 3D fracture network essential for enhanced geothermal systems. The findings also offer insights into upscaling induced seismicity from laboratory to field scale.

Link to paper:

Obermann, A., Rosskopf, M., Durand, V., Plenkers, K., Bröker, K., Rinaldi, A. P., et al. (2024). Seismic response of hectometer-scale fracture systems to hydraulic stimulation in the Bedretto underground laboratory, Switzerland. Journal of Geophysical Research: Solid Earth, 129, e2024JB029836. https://doi.org/10.1029/2024JB029836