PNNL

Abstract

Characterization of mining-related seismic events is critical to the implementation of the Comprehensive Nuclear-Test-Ban-Treaty monitoring system. Mine seismicity from uncontrolled sources is particularly troublesome, with magnitudes up to 4 or 5, producing signal strengths comparable to 1- to 10- kiloton contained nuclear explosions. In this study, ground motions from four surface stations and one underground station were inverted to determine the complete moment tensor of a relatively large rock burst in the Coeur d?Alene Mining District in northern Idaho. Many rock bursts, induced by the mining process, show implosional source mechanisms, a feature that should be useful to discriminate mining-related events from underground explosions. The rock burst analyzed in this study yielded seismograms with a moment tensor solution involving a significant volumetric component. The moment tensor was decomposed into isotropic and deviatoric components from which the volumetric closure and total shear deformation were estimated for comparison with in-mine co-seismic damage. The magnitude 3.1 burst occurred 7.5 hours after routine daily blasting in the mine. The event represented the result of deep underground mining combined with sliding on nearby bedding planes or faults. The implosional characteristic may prove to be a useful parameter for fingerprinting seismic events from deep hard rock mines.