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North Fork Valley Seismic Network — Fourth Quarter 2010 <br />Seismic Event Magnitudes <br />Of the 71 mining- related events, all were assigned magnitudes with the exception of the event on <br />20 December at 03:14 GMT (Table 3). M values assigned by Earthworm are also listed in <br />Table 3. The event on 11 December at 11:55 GMT of ML 3.0 was reported during this quarter by <br />NEIC as occurring within the bounds of Figure 2. <br />Recorded Peak Ground Accelerations <br />PGA values are generally recorded for all triggered events on the three- component <br />accelerometers. We have included the largest PGA recorded for each relocated seismic event in <br />Table 3 when available, along with the station that recorded the ground motion and the event -to- <br />station distance. The largest PGA recorded during the fourth quarter was 0.07 g at station MFB <br />for the 11 December M 3.0 event at a distance of approximately 1.29 km (0.80 mi). This event <br />occurred at the Bowie Mine. The largest PGA recorded at the West Elk Mine was 0.005 g at <br />station SPG resulting from the 11 December 14 :27 GMT M 1.8 seismic event that occurred at a <br />distance of approximately 0.90 km (0.56 mi). Note distances are approximate given <br />uncertainties in the event locations due to uncertainties in the velocity model used in the <br />relocations. <br />ACKNOWLEDGMENTS <br />The NFVSN data analysis and evaluation are jointly supported by MCC and BRL. Our thanks <br />to Wendell Koontz, MCC Project Manager, and Jim Abshire, BRL Project Manager for their <br />support. Our appreciation to Pete Swanson (NIOSH /CDS) for his operation and maintenance of <br />the network. Our thanks to Melinda Lee for her assistance in the preparation of this report. <br />REFERENCES <br />Banfill, R., 1995, PC -SUDS Utilities, A collection of tools for routine processing of seismic data <br />stored in the seismic unified data system for DOS (PC- SUDS). <br />Johnson, C.E., Bittenbinder, A., Bogaert B., Dietz L., and Kohler W., 1995, EW: A Flexible <br />Approach to Seismic Network Processing: IRIS Newsletter, v. 14, no. 2, p. 1 -4. <br />Koontz, W., 2007, Memorandum on the West Elk Mine B Seam Bounce on November 17, 2007, <br />2 p. <br />Swanson, P. and Koontz, W., 2006, Measurement and analysis of mining induced seismic <br />ground motion in the vicinity of the West Elk Coal Mine, Somerset, CO (abstract): <br />Seismological Research Letters, v. 77, no. 2, p. 318. <br />Swanson, P., Stewart, C., and Koontz, W., 2007, Installation of a digital, wireless, strong - motion <br />network for monitoring seismic activity in a western Colorado coal mining region, <br />Proceedings of the 20th Symposium on Application of Geophysics to Engineering and <br />Environmental Problems (SAGEEP), Environmental and Engineering Geophysical <br />Society, p. 559 -565. <br />um W:\X_WCFS \PROJECTS \WEST ELK -MTN COAL \2010 Q4 \Q4_2010_ MCC.DOC \18- MAR -1 1\ \OAK 5 <br />