Imaging of temporal stress redistribution due to triggered seismicity at a deep nickel mine

• Major events are associated with stress evolution at underground mines.
• Major events tend to occur in highly-stressed regions.
• Stress concentration and stress relief coexist in close proximity.
• Double-difference tomography can improve locating mining-induced seismicity.

We conducted three-dimensional passive seismic tomography surveys by using mining-induced seismicity of a deep nickel mine. To investigate the stress evolution with the distribution of major events, we collected location information of monitored seismicity and arrival time picks of waves transmitted from seismicity at the Creighton Mine in Sudbury, Ontario, Canada to produce velocity tomograms. From June 22nd to July 24th, 2011, four major events (moment magnitude >1.0) were observed associated with 13 630 microseismic events. We developed a large model and a small model, referring to scales of grid spacings and areas of territory, for double-difference tomographic inversion. The large model was used to examine the general trend of velocity distribution before and after the major events; the small model with finer grid spacing gave rise to a higher resolution to show results in detail. Seismic imaging results of velocity distribution showed good agreement with major events in different regimes, implying that the stress evolution was consistent with major events in the surrounding rock mass. By comparing the results obtained from tomographic inversion, we found that the stress in the region near major events started increasing before major events. High-stress areas, indicated by high-velocity anomalies, appeared and expanded adjacent to the region with major events.