Insights Into Complex Subdecimeter Fracturing Processes Occurring During a Water Injection Experiment at Depth in Äspö Hard Rock Laboratory, Sweden

• Published in: Journal of geophysical research. Solid earth 2018-08, Vol.123 (8), p.6616-6635
• Main Authors: Kwiatek, G., Martínez‐Garzón, P., Plenkers, K., Leonhardt, M., Zang, A., Specht, S., Dresen, G., Bohnhoff, M.
• Format: Article
• Language: English
• Subjects: Accelerometers; Acoustic emission; Activation; Boreholes; Broadband; Defects; Detection; Earthquakes; Energy; Experiments; Fluid injection; Fluid pressure; fracking; Geophysics; Hydraulic fracturing; Hydraulics; induced seismicity; Injection; Laboratories; maximum magnitude; Migration; Orientation; Parameters; Physical characteristics; Physical properties; picoseismicity; Pressure; Rocks; Seismic activity; Seismic energy; Seismicity; Seismographs; seismomechanics; Seismometers; Solutions; source parameters; Water depth; Water flooding; Water injection
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2017JB014715

We investigate the source characteristics of picoseismicity (Mw < −2) recorded during a hydraulic fracturing in situ experiment performed in the underground Äspö Hard Rock Laboratory, Sweden. The experiment consisted of six stimulations driven by three different water injection schemes and was performed inside a 28‐m‐long, horizontal borehole located at 410‐m depth. The fracturing processes were monitored with a variety of seismic networks including broadband seismometers, geophones, high‐frequency accelerometers, and acoustic emission sensors thereby covering a wide frequency band between 0.01 and 100,000 Hz. Here we study the high‐frequency signals with dominant frequencies exceeding 1000 Hz. The combined seismic network allowed for detection and detailed analysis of 196 small‐scale seismic events with moment magnitudes MW