ABSTRACT: U.S. Bureau of Mines researchers have analyzed full-waveform digital seismic records from moderate-to-large rockburst events at the Lucky Friday Mine, Mullan, ID. The goal of this work is to characterize source mechanisms for rockburst events. Because the seismometer array used for the recordings usually consists of fewer than 10 instruments, a method of obtaining composite source solutions has been developed. These solutions are determined by selecting events with similar arrival pat-terns at the seismometer array and with hypocentral locations in the same general region of the mine. Some events have all-dilatational first arrivals, while others display arrival patterns with both compressional and dilatational arrivals. There are at least three types of events in the mine. Some of the more complex arrival patterns seem to be associated with right-lateral, strike-slip motion, while others seem to be associated with left-lateral or dip-slip movement.

The type of event seems to be independent of source location, although geologic conditions in different regions vary. Even though there is a fundamental difference in the geometry of the mining environment, the three types of events are still recognizable.

This work is continuing, and data from all large events (Richter magnitude, mL > 2.0) at the mine are being analyzed and added to a database.

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