IMPROVEMENTS IN MINING INDUCED MICROSEISMIC SOURCE LOCATIONS AT THE LUCKY FRIDAY MINE USING AN AUTOMATED WHOLE-WAVE-FORM ANALYSIS SYSTEM

For years, severe rockburst problems at the Lucky Friday mine in north ern Idaho have been a persistent safety -hazard and an impediment to p roduction. An MP250 based microseismic monitoring system, which uses s imple voltage threshold picking of first arrivals, has been used in th is mine since 1973 to provide source locations and energy estimates of seismic events. Recently, interest has been expressed in developing a whole waveform microseismic monitoring system for the mine to provide more accurate source locations and information about source character istics. For this study, we have developed a prototype whole-waveform m icroseismic monitoring system based on a 80386 computer equipped with a 50 kHz analog-digital convertor board. The software developed includ es a data collection program, a data analysis program, and an event de tection program. Whole-waveform data collected and analyzed using this system during a three-day test have been employed to investigate sour ces of error in the hypocenter location process and to develop an auto matic phase picker appropriate for microseismic events. Comparison of hypocenter estimates produced by the MP250 system to those produced by the whole-waveform system shows that significant timing errors are co mmon in the MP250 system and that these errors caused a large part of the scatter evident in the daily activity plots produced at the mine. Simulations and analysis of blast data show that analytical control ov er the solutions is strongly influenced by the array geometry. Within the geophone array, large errors in the velocity model or moderate tim ing errors may result in small changes in the solution, but outside th e array, the solution is very sensitive to small changes in the data. Our whole-waveform detection program picks event onset times and deter mines event durations by analysis of a segmented envelope function (SE F) derived from the microseismic signal. The detection program has bee n tested by comparing its arrival time picks to those generated by hum an analysis of the data set. The program picked 87% of the channels th at were picked by hand with a standard error of 0.75 milliseconds. Sou rce locations calculated using times provided by our entire waveform d etection program were similar to those calculated using hand-picked ar rival times. In particular, they show far less scatter than source loc ations calculated using arrival times based on simple voltage threshol d picking of first arrivals.