2010-04-08_PERMIT FILE - C1996083

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. North Fork Valley Seismic Network — Fourth Quaver 2009 that important events are not missed. Earthworm also provides automatic locations for events that have sufficient arrival time picks. During the fourth quarter, Earthworm detected and located 2,118 events, not all of which were seismic events. Many more triggered waveform files were recorded, many of which have insufficient station data for locating the events. 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 M 1.7 or greater in size at the different mining locations and used that as a guide for selecting other events of approximate M 1.7 and larger. During the fourth quarter, the station OXM had timing problems (P. Swanson, NIOSH personal communications, 2010), which resulted in some erroneous Earthworm locations and overestimated MC values. We do not use these magnitudes in Table 3 and they are denoted by an asterisk. 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, XTRHY71, 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). P- and S -wave arrivals for events recorded on the temporary stations were picked using the Kinemetrics, Inc. program KMI File Viewer v. 1.8 (2005 -2007) and were manually added to the HYP071 input files. Only events with at least eight arrival time picks were located. The location accuracy usually improves as the number of stations increases. Table 2. Velocity Model Used in Locating Seismic Events • Depth to Top of layer (km) [mil Velocity (km /sec) [ft /sec] 0.00 [0.00] 2.21 [7,251] 0.07 [0.04] 2.73 [8,957] 0.27 [0.17] 3.01 [9,876] 0.37 [0.23] 3.18 [ 10,434] 1.00 [0.62] 3.9 [ 12,796] 1.50 [0.93] 4.60 [15,093] 2.50 [1.55] 5.20 [17,061] 3.50 [2.17] 6.00 [19,686] 6.00 [3.73] 6.5 [21,327] UM WAx_wcfs \PROJECTS \North Fork- Bowie\Quarterly reports\2009 Q4 \Q4_2009_BRL.d0C \0AK 3