Laserfiche WebLink
• North Fork Valley seismic Network — Fourth Quarter 2000 <br />SUMMARY <br />During the three -month period, 1 October to 31 December 2009, 46 mining - related seismic <br />events and one possible tectonic earthquake of approximate Richter local magnitudes NO 1.7 <br />and larger were relocated using data recorded on the North Fork Valley Seismic Network. Most <br />of the seismic events were located in two areas: the Elk Creek Mine and the Bowie Mine. A <br />total of 23 events occurred at the Bowie No. 2 Mine during this quarter. The largest event to <br />occur during this quarter was a M 2.1 event within the Bowie Mine area on 29 December. The <br />peak horizontal ground acceleration (PGA) for this event was 0.0001 g recorded at NOB at a <br />distance of 0.88 km (0.55 mi). No mining - related events were located in the vicinity of Bruce <br />Park Dam and the adjacent slump area. The highest PGA recorded during the fourth quarter of <br />2009 was 0.016 g at station FGH in the Bowie Mine area, which resulted from a coda duration <br />magnitude (M 1.8 event at a distance of about 1.08 km (0.67 mi). <br />INTRODUCTION <br />This report has been prepared in partial fulfillment of a commitment by Bowie Resources LLC <br />(BRL) 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 fourth quarter of 2009 (1 <br />October through 31 December). <br />The area included in this study encompasses the West Elk Mine, operated by Mountain Coal <br />Company, LLC (MCC) and Bowie No. 2 Mine, property of BRL (Figure 1). Seismicity from <br />Elk Creek Mine, owned by Oxbow Mining, Inc. is also recorded by the North Fork Valley <br />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, to provide event locations and magnitudes and <br />estimates of ground motions, and to determine focal mechanisms when feasible. Also, the <br />network will provide the fundamental data to develop a ground motion attenuation relationship <br />for the mining area and surrounding areas. The relationship will provide a means for predicting <br />ground motions from mining - related seismic events. Installation of the NFVSN was begun in <br />2006 and by October of that year, 5 stations were in operation (Swanson et al., 2007). By July <br />2006, 10 stations were operational. <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 />UM WAx_wcfs \PROJECTS \North Fork- Bowie \Quarterly reports\2009 Q4\Q4_2009_BRL.doC \OAK l <br />