2008-11-24_PERMIT FILE - C1996083 (5)

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North Fork Valley Seismic Network -Third Quarter 2001T We reviewed the daily summary or heliocorder records (these are continuous recordings of 12- hour periods conveniently plotted on one page) for filtered traces at three stations (WTM, LLM and WFW). We also reviewed the list of events automatically detected and located by Earthworm. Events were chosen based on amplitudes on the heliocorder records at the three stations. We measured the amplitudes on these heliocorder records for events known to be ML 1.5 or greater in size at the different mining locations and used that as a guide for selecting other events of approximate ML 1.5 and larger. Location Methodology We used the utility SUDSPICK in the program PC-SUDS (Banfill, 1996) to pick P- and S-wave arrival times within the DMX files (triggered waveform data files) for our selected list of events. Another utility within PC-SUDS, XTYHY71, was used to extract the arrival time picks from the waveform data files and convert them to the correct format to be used in the location program HYP071 (USGS, 1975). Only events with at least eight amval time picks were located. The location accuracy usually improves as the number of stations increases. A DOS version of the location program HYP071 was used to locate the seismic events. HYP071 requires aplane-layered velocity model, indicating depths to the top of each constant velocity layer, as well as station locations and arrival times, in order to relocate the seismic events. The velocity model (Table 2) was determined from a detailed seismic study at the West • Elk Mine (Swanson and Koontz, 2006). In that study, the recording stations were directly above the mining panel and so all the seismic rays were considered to be direct rays. This velocity model will be refined as further information is made available, particularly for recorded collapse 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 (6,500 ft [ 1.98 km]) and the velocity of the uppermost layer (7470 ft/sec [2.21 km/sec]). Table 2. Velocity Model Used in Locating Seismic Events Top of layer (km) [mi] Velocity (km/sec) [ft/sec] 0.00 [0.00] 2.21 [7,470] 0.07 [0.04] 2.73 [9,227] 0.27 [0.17] 3.01 [ 10,174] 0.37 [0.23] 3.18 [10,748] 1.50 [0.94] 3.96 [13,385] 2.50 [1.56] 4.40 [14,872] 6.00 [3.75] 6.00 [20,280] Magnitude Estimation Magnitudes in terms of ML were estimated for all mining-related events of ML 1.5 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. U~ W:UC_WCFS\PROJECTS\NORTH FORK-BOWIE\QUARTERLY REPORTS\2007 03\03_2007_BRL_FINAL.DOC112-FEB-OS\10AK 3