M. Kolaj¹ , N.J. Ackerley¹ , D. McCormack¹ , J. Adams¹

¹Canadian National Data Centre; Canadian Hazards Information Service, Natural Resources Canada

Abstract:

Many regions in Canada contain a mixture of natural seismicity of variable depth, low-magnitude explosions (arising from construction and/or mining activity) and mining induced events. Their correct classification is critical for seismic monitoring and for ensuring that anthropogenic events do not inflate seismic hazard calculations. Recently, local- to regional-spectral ratio discriminants across multiple phases and frequency bands have successfully been used in Canada to improve the accuracy and efficiency of event screening, particularly at low magnitudes (M < 3) where other explosion discriminants often fail. This work will present results from several case studies where spectral ratio discriminants have been used with varying degrees of success. In a test study in the New Brunswick, Canada, both high-frequency Pg/Lg and low-frequency Lg/Rg spectral ratios consistently discriminated between small (M < 2) blasts and earthquakes. In the mining-rich district of Sudbury, Canada, successful discrimination was possible for roughly 80 % of a test sample of M2 to M3 blasts and rockbursts. However, no single spectral ratio consistently provided adequate discrimination, and optimal spectral ratios needed to be calculated/tuned for particular stations. Preliminary results from other regions in Canada will also be presented.