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P-Wave polarity patterns from mining-induced microseismicity in a hard-rock mine.

Billington-S; Boler-FM; Swanson-PL; Estey-LH
Rock Mechanics: Contributions and Challenges: Proceedings of the 31st U.S. Symposium, June 18-20, 1990, Colorado School of Mines, Golden, Colorado. Hustrulid WA, Johnson GA, ed., Brookfield, VT: A.A. Balkema, 1990 Jan; :931-938
The Bureau of Mines is engaged in rock burst prediction and control research. One component of this research is directed toward applying quantitative seismological techniques of waveform analysis to the waveforms of elastic waves generated by microseismic events. These techniques can provide, from each microseismic event analyzed, in situ estimates of the orientation of the principal stress axes at the location of the event, the orientation of the slip (fault) plane on which the event took place, the direction of slip on that plane, the size of the slipped area, the co-seismic stress drop across the slip area, the amount of seismic energy released during the event, and the average amount of slip that occurred. Examination of these parameters from a suite of microseismic events may provide an indication of in situ changes in the physical state of the rock mass that are precursors to the larger seismic events in mines associated with rock bursts. Determining focal mechanism solutions from P-wave first motions (polarities) are a natural starting point for such analyses. At present, focal mechanism solutions for microseismic events are not available in our study area because the structure of the P-wave velocity field is not known well enough to accurately determine the potentially complicated ray paths to the accelerometers. However, an interim-stage analysis has been developed that allows microseismic events that have the same focal mechanism to be identified. Thus changes in the focal mechanisms of events can be tracked as a function of time and space and consequently used to infer changes in the stress state in time and space. This paper describes the interim-stage methodology and presents an example of its application to a set of microseismic events recorded in a hard-rock mine in northern Idaho.
Rock-mechanics; Mining-industry; Control-methods; Control-systems; Control-technology; Control-equipment; Engineering; Engineering-controls; Geology; Hard-rock-mines; Rock-bursts; In-situ-mining; Quantitative-analysis; Elastic-properties; Ground-control; Ground-stability; Environmental-control; Environmental-engineering; Environmental-stress; Analytical-processes; Wave-propagation
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OP; Conference/Symposia Proceedings
Hustrulid-WA; Johnson-GA
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NIOSH Division
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Rock Mechanics: Contributions and Challenges: Proceedings of the 31st U.S. Symposium, June 18-20, 1990, Colorado School of Mines, Golden, Colorado