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• <br />North Fork Valley Seismic NetworK -Third Quarter 2007T <br />SUMMARY <br />During the three-month period, 1 July to 30 September 2007, 187 mining-related seismic events <br />were relocated with approximate Richter local magnitudes (ML) 1.5 and larger using data <br />recorded on the North Fork Valley Seismic Network. Most of the seismic events were located in <br />four clusters: two at the Bowie No. 2 Mine, one at the Elk Creek Mine, and one at the West Elk <br />Mine, indicating the areas being worked at each of these mines. All the events observed in this <br />quarter appear to be mining-related. About one-third of the seismic events (54) occurred at the <br />Bowie No. 2 Mine. The two largest events located during this quarter, both ML 2.6, were located <br />at or close to the West Elk Mine and occurred on 9 and 15 August, respectively. The largest <br />event to occur at Bowie No. 2 Mine was an ML 2.1 event that occurred on 21 July. No mining- <br />related events were located in the vicinity of Bruce Park Dam or the landslide area. The highest <br />peak horizontal ground acceleration (PGA) recorded during the third quarter was 0.09 g at <br />station FGH in the Bowie Mine area which resulted from a ML 1.9 earthquake at a distance of <br />about 0.7 km (0.4 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 third quarter of 2007 (1 July <br />through 30 September). <br />The area included in this study encompasses the West Elk Mine, operated by Mountain Coal <br />Company, LLC and Bowie No. 2 Mine, property of 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 monitor the mining-related seismicity occurring in the <br />vicinity of the West Elk and Bowie No. 2 mines, provide event locations and magnitudes and <br />estimates of ground motions, and determine focal mechanisms when feasible. Also, the network <br />will provide the fundamental data to develop a ground motion attenuation relationship for the <br />mining area and surrounding areas. The relationship will provide a means for predicting ground <br />motions from mining-related seismic events. <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 />u~ W:1)C_WCFS\PROJECTS\NORTH FORK-BOWIE\QUARTERLY REPORTS\2007 03\Q3_2007_BRL_FINAL.DOC\12-FEB-08\\OAK 1 <br />