Observation and Modeling of Ripple-Fired Explosions at the Centralia Mine, Washington
- BATTELLE (PACIFIC NW LAB)
One of the issues associated with the Comprehensive Nuclear-Test-Ban Treaty (CTBT) is the discrimination of large mining explosions from nuclear tests. The Centralia coal mine is a significant source of seismic events in southwestern Washington. Some of the mine explosions have reported magnitudes as large as 3.5. We have assembled a set of waveform data from these explosions, derived from the Pacific Northwest Seismic Network and from broad band stations operated near the mine. Detailed information on the geometry and delay pattern of the explosions was used to simulate the mine signals. The most common set of delays was 25 and 84 ms within and between rows, respectively. This leads to a spectral reinforcement at 12 and 40 Hz. The use of 500-ms down-hole delays introduces an additional+/-3.5-ms scatter in the delay times, reducing but not eliminating the spectral peaks in the simulations. The blast simulations also predict spectral modulations resulting from the total blasting duration and the aspect ratio of the blast geometry (square vs. rectangular). A similar spectral modulation is observed in binary spectrograms and cepstra of many of the mine-generated signals. These spectral characteristics occur at lower frequencies than those related to the delay times, and so could be useful in identifying ripple-fired explosions at regional distances. An additional important source of low-frequency spectral modulation in the simulation is the ballistic duration of a spall source (material being lifted and re-impacting the surface). Properly modeling the spall source requires additional information about the explosion's effect on the blasted material that is difficult to document given the information typical in blasters' logs. Additional information such as charge weight, hole depth, and free-face orientation are being examined for their relation to groups of similar-appearing explosion sources.
- Research Organization:
- Pacific Northwest National Lab., Richland, WA (US)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 15002440
- Report Number(s):
- PNNL-SA-31835; NN2003000; TRN: US200416%%52
- Resource Relation:
- Conference: Proceedings of the 21st Seismic Research Symposium: Technologies for Monitoring the Comprehensive Nuclear-Test-Ban Treaty, Conference location not provided, Conference dates not provided; Other Information: PBD: 1 Sep 1999
- Country of Publication:
- United States
- Language:
- English
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