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• <br />North Fork Valley Seismic Network - First Quarter 2009 <br />SUMMARY <br />During the three-month period, 1 October to 31 December 2008, 57 mining-related seismic <br />events were relocated with approximate Richter local magnitudes (ML) 1.7 and larger using data <br />recorded on the North Fork Valley Seismic Network. Most of the seismic events were located in <br />two areas: one at the Elk Creek Mine, and one at the Bowie Mine. About 19% of the seismic <br />events (11) occurred at the Bowie No. 2 Mine. The largest events to occur during this quarter, <br />was a ML 2.9 event, which was located within the Elk Creek Mine area and occurred on <br />14 March. The largest event at the Bowie Mine was a ML 1.9 earthquake on 12 February 2009. <br />This event did not have a recorded PGA. No mining-related events were located in the vicinity <br />of Bruce Park Dam and the adjacent slump area. The highest peak horizontal ground <br />acceleration (PGA) recorded during the first quarter of 2009 was 0.13 g at station MFB in the <br />Bowie Mine area, which resulted from a coda duration magnitudes (Mc) 1.7 event at a distance <br />of about 0.69 km (0.43 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 first quarter of 2009 (1 January <br />through 31 March). <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. <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 />a repeater station, and uniform coverage of the target area (Figure 1). Each station consists of <br />three-component accelerometers. One temporary seismographic stations (OXM) operated during <br />M WAx_wcfs\PROJECTS\North Fork-Bowie\Quartedy reports\2009 Q1\Q1_2009_BRL.d0C\0AK 1