INTRODUCTION
High-resolution locations of microseismic events in mines would greatly augment the identification and mapping of geologic structures such as faults within the rock mass. Monitoring the movement and stress in the rock mass within the mining environment by microseismic analysis should aid in the understanding of rock bursting. Such monitoring by focal mechanism analysis is critically dependent upon high-resolution locations and accurate knowledge of the three-dimensional seismic velocity structure within the rock mass (Billington et al. 1990).
The Bureau of Mines is developing methods for such quantitative characterization of deformation by studying a working hard-rock mine located in the Coeur D'Alene district of northern Idaho which has discontinuous geologic structure. Routine locations of microseismic events in the mine at different stopes, based on arrival times of P-waves at different receivers, have been used to identify those stopes with a higher probability of bump or burst activity. Adding to this analysis by correlating individual events with known geologic structures, identifying and mapping unknown structures within the rock mass, and determining the direct causes of fracturing will require microseismic locations with high accuracy and precision. As a result, a current research direction is the identification of those parameters and/or numerical procedures which affect the computed location of a given microseismic event. The parameters considered here are the receiver coordinates, arrival time picks, and velocity field model. Numerical procedures include the location technique (i.e., basis function and numerical algorithm) and associated procedures such as receiver weighting, arrival weighting, and screening procedures.