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• North Fork Valley Seismic Network - First Quarter 2008 SUMMARY During the three-month period, 1 January to 31 March 2008, 143 mining-related seismic events were relocated with approximate Richter local magnitudes (ML) 1.7 and larger using data recorded on the North Fork Valley Seismic Network. Most of the seismic events were located in four clusters: one at the Bowie No. 2 Mine, two at the Elk Creek Mine, and one at the West Elk Mine. About 60% of the seismic events (84) occurred at the Bowie No. 2 Mine. The largest events to occur during this quarter, were four ML 2.3 events, two of which were located at the Bowie No. 2 Mine and occurred on 11 January and 19 February. The other two were located at the Elk Creek Mine. No mining-related events were located in the vicinity of Bruce Park Dam and the adjacent slump area. The highest peak horizontal ground acceleration (PGA) recorded during the first quarter of 2008 was 0.01 g at station MFB in the Bowie Mine area which resulted from the ML 1.9 event at a distance of about 0.9 km (0.6 mi). INTRODUCTION This report has been prepared in partial fulfillment of a commitment by Bowie Resources LLC (BRL) to monitor seismicity (including the microseismic activity near the longwall mining activity) in the North Fork Valley just east of Paonia, Colorado. This commitment is to the Colorado Department of Natural Resources, Division of Reclamation, Mining and Safety. This report contains preliminary analyses of the data collected for the first quarter of 2008 (1 January through 31 March). The area included in this study encompasses the West Elk Mine, operated by Mountain Coal Company, LLC (MCC) and Bowie No. 2 Mine, property of BRL (Figure 1). Seismicity from Elk Creek Mine, owned by Oxbow Mining, Inc. is also recorded on the North Fork Valley Seismic Network (NFVSN). The 10-station NFVSN was established to monitor the mining-related seismicity occurring in the vicinity of the West Elk and Bowie No. 2 mines, to provide event locations and magnitudes and estimates of ground motions, and to determine focal mechanisms when feasible. Also, the network will provide the fundamental data to develop a ground motion attenuation relationship for the mining area and surrounding areas. The relationship will provide a means for predicting ground motions from mining-related seismic events. NETWORK OPERATIONS The NFVSN consists of 10 permanent stations, which were installed as a cooperative effort between MCC, BRL and the Spokane Research Laboratory of the National Institute of Occupational Safety and Health/Centers for Disease Control and Prevention (NIOSH/CDC). The following factors were used to determine the station locations: access, permission of land owners, network geometry, radio line-of-sight to the common recording site at Paonia Airport or a repeater station, and uniform coverage of the target area (Figure 1). Each station consists of three-component accelerometers. Two temporary seismographic stations (NFG and TBW) were only operating during the first few days of the first quarter of 2008 at the Bowie No. 2 Mine (Figure 1) and so were not used in the location of most local events. The locations of tw W:\x_wcfslPROJECTS\North Fork-Bowie\Quarterly reports\2008 Q1\Qi_2008_BRL_final.doc\OAK I