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North Fork Valley Seismic Network - Third Quarter 2008 <br />SUMMARY <br />During the three-month period, 1 July to 30 September 2008, 347 mining-related seismic events <br />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 clusters: one at Elk Creek Mine and one at the Bowie Mine. Only about 5% of the seismic <br />events (16) occurred at the West Elk Mine. The largest event during this quarter was a ML 2.8 <br />event, which was located at the Elk Creek Mine. Other events that occurred at the West Elk <br />Mine were a ML 2.2 event on 11 September and a ML 2.0 event on 12 July. The highest peak <br />horizontal ground acceleration (PGA) recorded during the third quarter was 0.12 g at station <br />FGH in the Bowie Mine area which resulted from a ML 1.8 event at a distance of approximately <br />0.3 km (0.21 mi). The largest PGA recorded at the West Elk Mine was 0.02 g at station WFW <br />resulting from a ML 1.9 event that occurred on 28 August at a distance of approximately 0.85 km <br />(0.53 mi). <br />INTRODUCTION <br />This report has been prepared in partial fulfillment of a commitment by Mountain Coal Company <br />(MCC) 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 analyses of the data collected for the third quarter of 2008 (1 July through 30 <br />September). <br />The area included in this study encompasses the West Elk Mine, operated by MCC and Bowie <br />No. 2 Mine, property of Bowie Resources, LLC (BRL) (Figure 1). Seismicity from Elk Creek <br />Mine, owned by Oxbow Mining, Inc. is also recorded on the North Fork Valley Seismic Network <br />(NFVSN). <br />The 10-station NFVSN was established to (1) monitor the mining-related seismicity occurring in <br />the vicinity of the West Elk and Bowie No. 2 mines at a detection threshold magnitude of ML <br />1.0, (2) provide event locations and magnitudes and estimates of ground motions, and (3) <br />determine focal mechanisms when feasible. <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. The locations of seismographic stations operating during the <br />2008 third quarter are presented in Table 1 and shown on Figure 1. <br />UM W:V_WCFS\PROJECTS\WEST ELK-MTN COAL\2008 Q3\Q3_2008_ MCC.D0018-DEC-08\\OAK I