ICGCM Papers:
Rockmass Characterization/Hazard and Risk Assessment
 
 
Cross-Correlation Detection of Seismic Events Related to the Crandall Canyon Mine Collapse
32nd International Conference on Ground Control in Mining
Cross-Correlation Detection of Seismic Events Related to the Crandall Canyon Mine Collapse
by
Tex M KubackiKeith D KoperKristine L PankowMichael K Mccarter, University of Utah, Salt Lake City, United States
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[Conference] 32nd International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Rockmass Characterization/Hazard and Risk Assessment
[Author] Tex M KubackiKeith D KoperKristine L PankowMichael K Mccarter, University of Utah, Salt Lake City, United States
[Abstract] 
Key Conclusions:
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Cluster analysis of the known catalog reinforces previous work indicating the existence of seismicity on the east and west sides of the collapse. Research now demonstrates that it is possible to differentiate events related to the main collapse from those related to the rescue attempt following the collapse. Using cross-correlation and the regional seismic network (closest station 20 km distant), the magnitude of completeness was reduced from Mc 1.6 to Mc -0.5. This detection threshold approaches what can be obtained with an in-mine seismic network. Cross-correlation processing greatly improves the ability to detect small seismic events that accompany mining. This improved detection may lead to enhanced assessment of seismic hazards for conditions similar to Crandall Canyon.
Key Findings:
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A total of 531 seismic events were found to have occurred on the day of the collapse. Magnitudes as low as Mc -1.1 were detected. The magnitude of completeness was lowered from Mc 1.6 to Mc -0.5. A p-value of 0.71 was computed, indicating an aftershock decay sequence similar to those observed in other Utah coal mines. An additional 466 events were found to have occurred in the week leading up to the collapse. Many of the large catalogued events (>Mc 1.6) tend to be closely followed by numerous (often 20 or more) smaller aftershocks. Analysis of the known catalog shows four main event clusters: two to the east of the collapsed area and two to the west. Incorporation of cross-correlation lag times in double-difference relocation procedures results in a greater number of relocatable events.
Objective of the Paper:
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The objective of this paper is to present a revised and more complete study of the seismicity that occurred at the Crandall Canyon Mine during the month of August 2007. The research presented here focuses on the identification and analysis of small seismic events through cross-correlation and double-difference relocation techniques. These methods are presented in the interest of achieving a better understanding of mining-induced seismicity.
Problem Statement:
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On 6 August 2007, the Crandall Canyon Mine experienced a collapse which trapped six workers. An Mw 4.1 seismic event was recorded in conjunction with this collapse. An additional 54 related events were detected and located via routine processing techniques during the month of the collapse. Seismic cross-correlation can be used to detect very small tremors with similar waveforms to events in a known catalog. Using the 54 known events, it is possible to perform sliding cross-correlations with continuous seismic data recorded at five nearby monitoring stations (~20 km away). This procedure results in hundreds of new detections, and provides useful clustering information which helps to detail the sequence of the collapse.