2011-06-06_REPORT - C1980007 - Laserfiche WebLink

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North Fork Valley Seismic Network — First Quarter 2011 SUMMARY During the three -month period from 1 January to 31 March 2011, 84 mining- related seismic events of approximate coda magnitudes (M 1.7 and larger were relocated using data recorded on the North Fork Valley Seismic Network. Most of the seismic events were located at the Elk Creek Mine. Only three seismic events occurred within the West Elk Mine permit area. The events were all M 1.8 and were located away from the area of active mining. The largest event during this quarter was a Richter local magnitude (M 3.1 event at Elk Creek Mine. The highest peak horizontal ground acceleration (PGA) observed during the first quarter was 0.007 g recorded at station MFB in the Bowie Mine area resulting from the Mc 1.7 event at a distance of approximately 0.92 km (0.57 mi). The largest PGA recorded at the West Elk Mine was only 0. 000 15 g at station SPG resulting from a M 1.8 event on 21 March located approximately 6.76 km (4.2 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 first quarter of 2011 (1 January through 31 March). 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, five 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. A permanent station was installed at Fire Mountain (FMT) and began operations at Oxbow Mine in October 2010. The following factors were used to determine the station locations: access, permission of land owners, network geometry, radio WAX _WCFS \PROJECTS\WEST ELK -MT N COAL \2011 Q1 \Q1_2011_MCC. DOC\27- MAY- 11 \\OAK 1