Seismic signals from underground cavity collapses and other mining-related failures
The sudden collapse of man-made underground cavities have generated seismic signals as large as magnitude 5.4. Collapses are just one of the many types of mining associated seismicity including coalbumps and rockbursts which need to be identified and distinguished from potential clandestine nuclear explosions under the recently signed Comprehensive Test Ban Treaty (CTBT). Collapses, coalbumps and rockbursts are of concern for seismically monitoring a CTBT for a number of reasons. First, they can look like explosions when using some seismic discriminant measures, such M{sub s}:m{sub b}, M{sub o}: m{sub b}, regional P/S ratios and depth. Second, underground nuclear explosions themselves produce cavities that might collapse, possibly aiding in the detection of a clandestine event. Finally, because all mine-related events occur in the vicinity of underground cavities, they may come under special scrutiny because of the concern that very large, specially constructed cavities could be used to evasively decouple a clandestine test. For these reasons mine-related seismicity in both active and former mining regions have the potential to be false alarms under a CTBT. We are investigating techniques to identify collapses, either directly via waveform modeling, or indirectly by combining several seismic discriminants. We are also investigating the source mechanisms of coalbumps and collapses to better understand the performance of seismic discriminants for these events. In particular we have found similarities in point source models of some longwall coalbumps, room- and-pillar mine collapses and NTS nuclear explosion cavity collapses. In order to understand coalbumps we are analyzing events from central Utah recorded at regional distances in Utah and Nevada including at the auxiliary station ELK. Some of these have anomalous, explosion- like high frequency P/S ratios. We are combining this new study with results from previous field work done in 1995 at a Colorado long-wall coal mining operation. Similarly to longwall coal mines in Utah and elsewhere, this Colorado mine completely excavates a 3m high coal seam in 250 m wide panels leaving the material above unsupported. The roof material above the excavated seam eventually collapses resulting in seismic events.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 611778
- Report Number(s):
- UCRL-JC-127899; CONF-970967-; ON: DE98051133
- Resource Relation:
- Conference: Research symposium on monitoring a comprehensive test ban treaty, Orlando, FL (United States), 23-25 Sep 1997; Other Information: PBD: 1 Jul 1997
- Country of Publication:
- United States
- Language:
- English
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