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<br />North Fork Valley Seismic Network - Second Quarter 2008 <br />located 2004 events, not all of which were seismic events. Many more triggered waveform files <br />were recorded, many of which have insufficient station data for locating the events. <br />We reviewed the daily summary or heliocorder records (these are continuous recordings of 12- <br />hour periods conveniently plotted on one page) for filtered traces at three stations (WTM, LLM <br />and WFW). We also reviewed the list of events automatically detected and located by <br />Earthworm. Events were chosen based on amplitudes on the heliocorder records at the three <br />stations. We measured the amplitudes on these heliocorder records for events known to be ML <br />1.7 or greater in size at the different mining locations and used that as a guide for selecting other <br />events of approximate ML 1.7 and larger. <br />Location Methodology <br />We used the utility SUDSPICK in the program PC-SUDS (Banfill, 1996) to pick P- and S-wave <br />arrival times within the DMX files (triggered waveform data files) for our selected list of events. <br />Another utility within PC-SUDS, XTYHY71, was used to extract the arrival time picks from the <br />waveform data files and convert them to the correct format to be used in the location program <br />HYP071 (USGS, 1975). P- and S-wave arrivals for events recorded on the temporary stations <br />were picked using the Kinemetrics, Inc. program KMI File Viewer v. 1.8 (2005-2007) and were <br />manually added to the HYP071 input files. Only events with at least eight arrival time picks <br />were located. The location accuracy usually improves as the number of stations increases. <br />Table 2. Velocity Model Used in Locating Seismic Events <br />Depth to Top of layer (km) <br />[mil Velocity (km/sec) [ft/sec] <br />0.00 [0.00] 2.21 [7,251] <br />0.07 [0.04] 2.73 [8,957] <br />0.27 [0.17] 3.01 [9,876] <br />0.37 [0.23] 3.18 [10,434] <br />1.00 [0.62] 3.9 [12,796] <br />1.50 [0.93] 4.60 [15,093] <br />2.50 [1.55] 5.20 [17,061] <br />3.50 [2.17] 6.00 [19,686] <br />6.00 [3.73] 6.5 [21,327] <br />A DOS version of the location program HYP071 was used to locate the seismic events. <br />HYP071 requires a plane-layered velocity model, indicating depths to the top of each constant <br />velocity layer, as well as station locations and arrival times, in order to relocate the seismic <br />events. The velocity model (Table 2) was determined from a detailed seismic study at the West <br />Elk Mine (Swanson and Koontz, 2006). In that study, the recording stations were directly above <br />the mining panel and so all the seismic rays were considered to be direct rays. This velocity <br />model will be refined as further information is made available, particularly for recorded events <br />UM W:\x_WCfs\PROJECTS\North Fork-Bowie\Quartedy reports\2008 Q2\Q2_2008_BRL.d0C\0AK 3