MINING-INDUCED SEISMICITY IN FAULTED GEOLOGIC STRUCTURES - AN ANALYSIS OF SEISMICITY-INDUCED SLIP POTENTIAL

Relationships between the locations of mining-induced seismic events, local fault structure, and mine geometry were examined in a deep hard-rock mine in northern Idaho. Stopes experiencing rock bursts and other large seismic events were found to fall into two structural regimes: the ''Silver Vein,'' and the ''N48-degrees-W Trend,'' a steeply dipping plane of seismic activity that is subparallel to major local steeply dipping faults which bound blocky structures. The N48-degrees-W Trend also intersects a shaft that was seriously damaged when fault gouge was expelled into the opening during a 3-month period of high seismic energy release. Models of stress interaction are used to support the hypothesis that mining-induced deformation was mobilized along a 1.5 km length of the N48-degrees-W Trend. Specifically, numerical models are used to simulate rupture of seismic events and estimate induced changes in the quasi-static stress field. A Coulomb failure criterion is used with these results to estimate the spatial variation in potential for slip on planes parallel to local faulting. Increases in the potential for slip on fault planes subparallel to the N48-degrees-W Trend are consistent with activation of deformation along its 1.5 km length. For events with constant seismic moment, stress drop is shown to be far more important than source dimension in elevating slip potential along the observed plane of seismic activity.