To assess objectively the source mechanism of mining‐induced seismic events, we developed an algorithm to invert for the moment tensor components. From this inversion, the ratio of isotropic/deviatoric component in the source is obtained. We are applying this method to microseismic events (−4<M<−2) recorded at the Underground Research Laboratory (URL) in Pinawa, Manitoba, where a tunnel is being excavated at 420 m depth. To monitor the seismic activity induced by this opening an array of 16 triaxial accelerometers was installed around the planned tunnel. Results from the moment tensor inversion on a fist data set provide evidence of non‐shear failure mechanisms. Furthermore, the location of events displaying a tensile component corresponds to a breakout observed underground in the roof of the tunnel.
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Feignier et al. (1992) studied this question.