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North Fork Valley Seismic Network - First Quarter 2008 <br />SUMMARY <br />During the three-month period, 1 January to March 2008, 143 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 />four clusters: one at the Bowie No. 2 Mine, two at the Elk Creek Mine, and one at the West Elk <br />Mine. About 22% of the seismic events (31) occurred at the West Elk Mine. The largest events <br />during this quarter were four ML 2.3 events, two of which were located at the Bowie No. 2 Mine <br />and two at the Elk Creek Mine. The largest events to occur at the West Elk Mine were two ML <br />2.2 events on 26 January and 23 February 2008. The highest peak horizontal ground acceleration <br />(PGA) recorded during the first quarter was 0.01 g at station MFB in the Bowie Mine area which <br />resulted from a ML 1.9 event at a distance of approximately 0.9 km [0.6 mi]. The largest PGA <br />recorded at the West Elk Mine was 0.003 g at station WFW resulting from a ML 2.0 event that <br />occurred on 14 February at a distance of approximately 0.8 km [0.5 mil. <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 preliminary analyses of the data collected for the first quarter of 2008 (1 January <br />through 31 March). <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). Seismicity from Elk Creek Mine, owned <br />by Oxbow Mining, Inc. is also recorded on the North Fork Valley 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 at a detection threshold magnitude of ML 1.0, <br />provide event locations and magnitudes and estimates of ground motions, and to determine focal <br />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 first quarter are presented in Table 1 and shown on Figure 1. <br />1W W:U(_WCFS\PROJECTS\WEST ELK-MTN COAL\2008 Q1\Q1_2008_MCC_FINAL.DOC\18-MAY-08\\OAK I