In many underground mines, seismic monitoring is simply used to identify a spatial distribution of seismic activity due to local rock mass failure or large events, and this information is then used to identify potential safety hazards to workers and mine openings. In the last few years, many mines in Canada have used microseismic data to enhance an established protocol for re-entry into seismically active areas following large rockburst events.

The simplest techniques make use of microseismic event decay rate following large rockbursts as a tool for establishing re-entry time. In some cases, however, it has been found that this method has limitations and other seismic parameters can be more useful to establish if the rock mass has settled to a ‘background’ level of seismicity. A case study is presented from INCO’s North Mine, located in Sudbury Ontario. The seismicity associated with three rockbursts, which occurred between September 2004 and June 2005 was analyzed in order to establish parameter thresholds for re-entry. The seismic data were recorded by a 64 channel microseismic system from 46 uniaxial and 3 triaxial accelerometers installed underground. Observational data collected were used to relate the state of the rock mass following the rockbursts to the trends in the seismicity. The goal of this study was to determine a set of seismic parameters and establish thresholds to be used as part of the rockburst re-entry protocol at North Mine.

F. Malek, M. Sc., P.Eng., Ground Control Engineer
Copper Cliff North Mine, INCO Ltd., Sudbury, Ontario Canada

I. S. Leslie, M. Sc.
ESG Canada, Kingston, Ontario, Canada