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• <br />North Fork Valley Seismic Network - Fourth Quarter 2007 <br />SUMMARY <br />During the three-month period, 1 October to 31 December 2007, 227 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 />three clusters: one at the Bowie No. 2 Mine, one at the Elk Creek Mine, and one at the West Elk <br />Mine. About 61% of the seismic events (139) occurred at the Bowie No. 2 Mine. The largest <br />event to occur during this quarter, a ML 3.4 event, was located at the West Elk Mine and <br />occurred on 11 November. Minor damage was reported at the West Elk Mine, mostly rib <br />spalling and possible floor heave. Two ML 3.2 events also occurred at the West Elk Mine on 5 <br />November and 2 December. The largest event to occur at Bowie No. 2 Mine was an ML 2.9 <br />event that occurred on 3 November. This was one of three events experienced underground in <br />the 1 East Mains development section. No mining-related events were located in the vicinity of <br />Bruce Park Dam or the landslide area. The highest peak horizontal ground acceleration (PGA) <br />recorded during the fourth quarter was 0.04 g at station MFB in the Bowie Mine area which <br />resulted from the ML 2.9 event at a distance of about 0.1 km (0.1 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 fourth quarter of 2007 (1 <br />October through 31 December). <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 on 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, provide event locations and magnitudes and <br />estimates of ground motions, and determine focal mechanisms when feasible. Also, the network <br />will provide the fundamental data to develop a ground motion attenuation relationship for the <br />mining area and surrounding areas. The relationship will provide a means for predicting ground <br />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 />UM WAx wcfS\PROJECTS\North Fork-BoWe\Quarterly reports\2007 Q4\Q4 Final Report 030308\Q4_2007_BRL_Final_030308.doc\0AK 1