INTRODUCTION
Mining concentrates stress that can cause rock to explode or "burst" into a stope or drift without warning. Rock bursts pose severe safety and productivity problems for deep mines throughout the world, particularly in strong, brittle rock masses where narrow, tabular ore bodies are mined to high extraction ratios (Blake 1987). Such is the case in the Coeur d'Alene Mining District of northern Idaho where rock bursting has been a problem for nearly 50 years. The Bureau of Mines has worked closely with mining companies to study rock burst phenomena, and several burst controls have been developed, such as destressing, preconditioning, stope sequencing, and single level mining (Karwoski et al. 1979; Jenkins and Dorman 1983).
Although the complex mechanisms that produce rock bursts are still not completely understood, researchers have identified four major causes (Hedley 1987):
1. Surface instabilities at or near a stope face. These instabil-ities are characterized by spalling of the free surface.
2. Propagation of shear fractures in the rock mass ahead of the work-ing face.
3. Sudden collapse of overstressed pillars.
4. Slip along existing geologic features such as faults or bedding surfaces.
Type 1 and 2 rock bursts are generally associated with drift or stope excavations and result in relatively small volumes of rock exploding into an opening. Type 3 and 4 bursts are generally larger-scale events that occur when extensive mining creates instabilities over an area of the mine.
Advances in seismology have stimulated the use of seismic techniques to investigate rock burst mechanisms. Seismic emissions can be detected almost continually in deep mines and their frequency and intensity are directly related to rock mass instability. The Bureau recognized microseismic technology as a potential tool for rock burst prediction as early as 1939 (Obert 1939); however, only a few successful predictions have been achieved to date.