2008-11-24_PERMIT FILE - C1996083 (11)

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• North Fork Valley Seismic Network - Fourth Quarter 2007 events with known locations. Station elevation corrections (Table 1) were incorporated into the location program based on the elevation differences between the station and the velocity model datum (7938 ft [2420m]) and using a weighted average velocity over the layers between the datum and the station elevation. Magnitude Estimation Magnitudes in terms of ML were estimated for all mining-related events of ML 1.7 and greater based on peak amplitudes as recorded on the Mesa State Seismic Network (MSSN) operated by David Wolny. The standard Richter magnitude formula was used to calculate the ML values. Magnitude uncertainties are typically 0.1 to 0.2 magnitude units based on comparisons with magnitudes of larger events as estimated by the USGS National Earthquake Information Center (NEIL) in Golden, Colorado (D. Wolny, personal communication, 2007). Coda duration magnitudes (MC) are also automatically calculated by Earthworm based on a USGS northern California formula. Mc values are approximately the same as ML. RESULTS Mining Progress The locations of longwall, continuous miner during the fourth quarter are shown on Figure 2 active during the quarter. (CM) and D-seam pillar mining that occurred . Figure 2 also shows the mining areas that were Mining activities were relatively normal during the quarter in all sections except in the 1 East Mains CM development section (Figure 2). Mining was terminated in this section upon directions from the Mine Safety and Health Administration after three bumps occurred on 2 October (ML 2.1), 20 October (ML 1.7), and 3 November (ML 2.9). (See following discussion.) Pillar retreat mining was completed in the D-seam in November 2007. Seismic Event Locations Table 3 lists the events recorded and relocated in the fourth quarter (ML >_ 1.7). The date and origin time (hours, minute, and second) of the event, location (latitude, longitude, and general area), magnitudes, and largest PGA values are listed. Figure 3 shows the resulting locations for the 227 seismic events of approximate ML 1.7 and larger. The majority of mining-related seismic events cluster in three areas generally indicating where the mining activity occurred during this quarter. Approximately 139 events can be associated with the Bowie mining operations. The activity at Bowie No. 2 Mine corresponds reasonably well with the location of mining activity during the quarter (Figure 3). There is one large cluster of events at the Bowie No. 2 Mine, centered over the central portion of the mine where active longwall mining was occurring with some events occurring in the surrounding areas of mining activity (Figure 3). The cluster is located about 2.5 km (1.6 mi) north-northwest of Bowie No. 2 (Figure 3). No mining-related seismic events were located in the vicinity of Bruce Park Dam or the landslide area (Figure 3). UM WAx_wcfs\PROJECTS\North Fork-Bowie\Quarterly reports\2007 Q4\Q4 Final Report 030308\Q4_2007_BRL_Final_030308.doe\OAK 4