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Three-dimensional velocity tomograms were generated on a daily basis to image mining-induced changes to the overburden above a longwall mine. The hypothesis was that a coherent redistribution of seismic velocity, due to the development of high-stress zones, could be imaged at the mine scale. Seam depth was 360 m and source location depth varied from 100 to 1000 m. Sixteen geophones were distributed over a 600 by 600 m square area on the surface above the mine. More than 12,500 events were recorded over an 18 day period. The recorded seismicity provided input for the local-earthquake tomography code, SIMULPS. Eighteen tomograms were generated and high-velocity regions correlated well with high abutment stresses. Additionally, the high-velocity regions were observed to redistribute as the longwall face retreated. These results indicate that velocity tomography can be used to provide a better understanding of temporal changes within a rock mass, and can potentially be used to produce a better understanding of the mechanisms that lead to unanticipated ground failures.
| Author(s): | Westman-EC, Luxbacher-KD, Swanson-PL |
| Reference: | 42nd U.S. Rock Mechanics Symposium/2nd U.S.-Canada Rock Mechanics Symposium, June 29 - July 2, 2008, San Francisco, California, ARMA 08-299. The American Rock Mechanics Association, 2008; :1-7 |
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