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• <br />North Fork Valley Seismic Network - Second Quarter 2009 <br />SUMMARY <br />During the three-month period, 1 April to 30 June 2009, 44 mining-related seismic events were <br />relocated with approximate Richter local magnitudes (ML) 1.7 and larger using data recorded on <br />the North Fork Valley Seismic Network. Most of the seismic events were located in two areas: <br />the Elk Creek Mine and the Bowie Mine. Only three events occurred at the Bowie No. 2 Mine <br />during this quarter. The largest event to occur was a coda duration magnitude (Mc) 2.3 event, <br />which was located within the Elk Creek Mine area and occurred on 7 June. The largest event at <br />the Bowie Mine was a ML 2.1 earthquake on 28 May 2009. The peak horizontal ground <br />acceleration (PGA) for this event was 0.004 g recorded at BWK g at a distance of 2.12 km (1.32 <br />mi). No mining-related events were located in the vicinity of Bruce Park Dam and the adjacent <br />slump area. The highest PGA recorded during the second quarter of 2009 was 0.007 g at station <br />BWK in the Bowie Mine area, which resulted from a ML 1.8 event at a distance of about 2.52 km <br />(1.57 mi). <br />INTRODUCTION <br />This report has been prepared in partial fulfillment of a commitment by Bowie Resources LLC <br />(BRL) to monitor seismicity (including the microseismic activity near the longwall mining <br />activity) in the North Fork Valley just east of Paonia, Colorado. This commitment is to the <br />Colorado Department of Natural Resources, Division of Reclamation, Mining and Safety. This <br />report contains preliminary analyses of the data collected for the second quarter of 2009 (1 April <br />through 30 June). <br />The area included in this study encompasses the West Elk Mine, operated by Mountain Coal <br />Company, LLC (MCC) and Bowie No. 2 Mine, property of BRL (Figure 1). Seismicity from <br />Elk Creek Mine, owned by Oxbow Mining, Inc. is also recorded by the North Fork Valley <br />Seismic Network (NFVSN). <br />The 10-station NFVSN was established to monitor the mining-related seismicity occurring in the <br />vicinity of the West Elk and Bowie No. 2 mines, to provide event locations and magnitudes and <br />estimates of ground motions, and to determine focal mechanisms when feasible. Also, the <br />network will provide the fundamental data to develop a ground motion attenuation relationship <br />for the mining area and surrounding areas. The relationship will provide a means for predicting <br />ground motions from mining-related seismic events. Installation of the NFVSN was begun in <br />2006 and by October of that year, 5 stations were in operation (Swanson et al., 2007). By July <br />2006, 10 stations were operational. <br />NETWORK OPERATIONS <br />The NFVSN consists of 10 permanent stations, which were installed as a cooperative effort <br />between MCC, BRL and the Spokane Research Laboratory of the National Institute of <br />Occupational Safety and Health/Centers for Disease Control and Prevention (NIOSH/CDC). <br />The following factors were used to determine the station locations: access, permission of land <br />owners, network geometry, radio line-of-sight to the common recording site at Paonia Airport or <br />um WAx_wcfs\PROJECTS\North Fork-Bowie\Quarterly reports\2009 Q2\Q2_2009_BRL.d0C\0nK 1