SOURCE PARAMETERS OF MINING-INDUCED SEISMIC EVENTS - AN EVALUATION OFHOMOGENEOUS AND INHOMOGENEOUS FAULTING MODELS FOR ASSESSING DAMAGE POTENTIAL

Source parameter estimates based on the homogeneous and inhomogeneous source models have been examined for an anomalous sequence of seven mi ne-induced events located between 640 and 825 m depth at Strathcona mi ne, Ontario, and having magnitudes ranging between m(N) 0.8 and 2.7. T he derived Brune static stress drops were found to be similar to those observed for natural earthquakes (similar to 30 bars), whereas dynami c stress drops were found to range up to 250-300 bars. Source radii de rived from Madariaga's model better fit documented evidence of undergr ound damage. These values of source radii were similar to those observ ed for the inhomogeneous model. The displacement at the source, based on the observed attenuation relationship, was about 60 mm for three ma gnitude 2.7 events. This is in agreement with slip values calculated u sing peak velocities and assuming the asperity as a Prune source withi n itself (72 mm). By using Madariaga's model for the asperity, the sli p was over 3 times larger than observed. Peak velocity and acceleratio n scaling relations with magnitude were investigated by incorporating available South African data, appropriately reduced to Canadian geophy sical conditions. The dynamic stress drop scaled as the square root of the seismic moment, similar to reported results in the literature for crustal earthquakes. This behavior suggests that the size of the aspe rities responsible for the peak ground motion, with respect to the ove rall source size, follow distributions that may be similar over a wide range of magnitudes. Measurements of source rupture complexity (rangi ng from 2 to 4) were found to agree with estimates of overall source t o asperity radii, suggesting, together with the observed low rupture v elocities (0.3 beta to 0.6 beta), that the sources were somewhat compl ex. Validation of source model appropriateness was achieved by direct comparison of the predicted ground motion level to observed undergroun d damage in Creighton mine, located within the same regional stress an d geological regime as Strathcona mine. Close to the source (<100 m), corresponding to relatively higher damage levels, a good agreement was found between the predicted peak particle velocities for the inhomoge neous model and velocities derived based on established geomechanical relationships. The similarity between asperity radii and the regions o f the highest observed damage provided additional support for the use of the inhomogeneous source model in the assessment of damage potentia l.