The Influences of Stress and Structure on Mining-induced seismicity in Creighton Mine, Sudbury, Canada
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The Creighton Mine is a structurally complex and seismically active mining environment. Microseismic activity occurs daily and increases with depth, complicating downward mine expansion. Larger magnitude events occur less frequently but can damage mine infrastructure, interrupt operations and threaten worker safety. This thesis explores the relationships between geological structure and mining-induced seismicity through geological, seismological and numerical modelling investigations in an area known as the Creighton Deep, with concentration on the 7400 Level (2255 m). Geological features within the Creighton Deep have a reported association with seismic activity. Four families of shear zones were identified during field investigations, the most prominent striking SW and steeply dipping NW. Seismicity from 2006-2007 is analyzed. Spatial and temporal trends and seismic event parameters show little correlation to shear zone geometry. Instead, seismic event parameters correlate to spatial clusters of events. A remote cluster of events to the southwest of the excavation exhibits anomalously high seismic parameter values. This area of the mine continues to be a source of elevated seismicity. Fault plane solutions are utilized to compare shear zone geometry with active slip surfaces. Solutions for macroseismic events are inconsistent, while microseismic event focal mechanisms have similar pressure, tension and null axes. The resulting solutions do not align with shear-zone orientations. A stress inversion using microseismic focal mechanism information yields a stress tensor that is comparable to the regional stress tensor. Universal Distinct Element Code numerical models demonstrate that a yield zone exists immediately surrounding the excavation. SW-striking shear zones modify the stress field, resulting in increased stress to the southeast of the excavation. These high-stress zones are areas of preferred seismic activity. Slip is induced on select SW-striking shear zones to the south of the excavation as well as localized yielding. The characteristics of mining-induced seismicity do not correlate to shear zones. Seismicity does compare to modelled stress: the yielded rock mass adjacent to the excavation has little seismicity; areas of high stress are areas of rock mass damage and dense seismic activity. It is thus proposed that seismicity in the Creighton Deep results from stress-induced rock mass degradation rather than fault-slip.