2011-06-01_REPORT - C1980007 (3)

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North Fork Valley Seismic Network — Second Quarter 2010 SUMMARY During the three -month period from 1 April to 30 June 2010, 35 mining - related seismic events of approximate Richter local magnitudes (ML) 1.7 and larger were relocated using data recorded on the North Fork Valley Seismic Network. Most of the seismic events were located in two areas: at the Elk Creek Mine and at the Bowie Mine. Only 5 seismic events occurred within the West Elk Mine permit area. The largest event during this quarter was a coda magnitude (M 2.5 event at Bowie Mine. The largest event at the West Elk Mine was a M 2.2 event on 26 April north of the area of active mining. The highest peak horizontal ground acceleration (PGA) observed during the second quarter was 0.002 g recorded at station BWK in the Bowie Mine area resulting from a M 1.9 event at a distance of approximately 0.94 km (0.58 mi). The largest PGA recorded at the West Elk Mine was only 0.0004 g at station MCD resulting from the 18 April Mc 1.9 event located approximately 4.68 km (2.91 mi) away. INTRODUCTION This report has been prepared in partial fulfillment of a commitment by Mountain Coal Company (MCC) 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 analyses of the data collected for the second quarter of 2010 (1 April through 30 June). The area included in this study encompasses the West Elk Mine, operated by MCC and Bowie No. 2 Mine, property of Bowie Resources, LLC (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 (1) monitor the mining- related seismicity occurring in the vicinity of the West Elk and Bowie No. 2 mines at a detection threshold magnitude of M 1.0, (2) provide event locations and magnitudes and estimates of ground motions, and (3) determine focal mechanisms when feasible. Installation of the NVFSN was begun in 2006 and by October of that year, 5 stations were in operation (Swanson et al., 2007). By July 2006, 10 stations were operational. NETWORK OPERATIONS The NFVSN consists of 10 permanent stations (Table 1 and Figure 1), 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). One temporary station OXM was installed in February 2009 and has remained as part of the network (Table 1 and Figure 1). A semi - permanent station, NOB, was installed in November 2009 in the Bowie Mine area. 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 I= W:\X_WCFS \PROJECTS \WEST ELK -MTN COAL \2010 Q2 \Q2_2010_ MCC. DOC\31 -AUG-1 0\\OAK 1