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North Fork Va11ev Seismic Network - Fourth Quarter 2009 <br />Seismic Event Magnitudes <br />Of the 46 mining-related events, only 35 were assigned magnitudes (Table 3). ML values were <br />assigned to 15 events by Dave Wolny (written communications, 2008) as determined from the <br />MSSN. Coda duration magnitudes (Mc) values assigned by Earthworm are also listed in <br />Table 3. <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 quarterly period was 0.016 g at station <br />FGH for a Mc 1.8 event at a distance of approximately 1.08 km (0.66 mi). This event occurred <br />on 1 I November 2009 10:09 GMT at the Bowie No. 2 Mine. The largest PGA recorded at the <br />West Elk Mine was 0.0006 g at station WFW resulting from the 3 November 19:21 GMT ML 1.8 <br />seismic event that occurred at a distance of approximately 1.98 km (1.23 mi). Note distances are <br />approximate given uncertainties in the event locations due to uncertainties in the velocity model <br />used in the relocations. <br />ACKNOWLEDGMENTS <br />The NFVSN data analysis and evaluation are jointly supported by MCC and BRL. Our thanks to <br />Wendell Koontz, MCC Project Manager, and Jim Abshire, BRL Project Manager for their <br />support. Our appreciation to Pete Swanson (NIOSH/CDS) and Dave Wolny (Mesa State <br />College) for their assistance in the operation and maintenance of the network. Our thanks to <br />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 />UM WAX_WUMPROJECTS\WEST ELK-MTN COAL\2009 Q4\Q4_2009_MCC.DOC\2-MAR-10\\OAK 5