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• Seismic Monitoring Network at Bowie Resources Longwall Coal Mine <br />Long <br />Objective: Deploy seismic monitoring array to provide continuous measure of seismic activity <br />in the vicinity of past, present, and future longwall mining activity. Collect data to investigate <br />empirical ground motion relations. <br />Area Covered: Area bounded by Hubbard Creek on the east, Terror Creek on the west, Terror <br />Creek reservoir on the north, and county road 133 on the south. <br />Seismology Basics: Discrete ground adjustments that occur during mining generate seismic <br />waves that are detected and recorded by in array of seismic sensors. Measurement of relative <br />arrival times of seismic waves at different seismic stations provides the basic data needed to <br />calculate "event" locations. A realistic seismic velocity model of the region must be constructed <br />for use in the location calculations. Recording and analyzing full seismic waveforms allows <br />magnitude, or other measures of strength, to be estimated and the time history of ground motions <br />to be identified. Ground motions that are strong enough to potentially represent a threat to <br />engineerinyo structures are called strong ground motions. Strong-motion seismographs, or <br />accelerographs, are specifically designed to measure strong ground motions near seismic <br />sources. These units measure three-dimensional ,round acceleration (one vertical and two <br />horizontal components) as a function of time. Integration of the acceleration time series yields <br />;"round velocities and displacements as a function of time. Parameters for characterizing ground <br />motion include peak ground acceleration (PGA), peak ground velocity (PGV) and displacement <br />• POD), duration of shaking. and various response spectra. <br />Network Monitoring Concept: Standard hardware and software methods of earthquake <br />seismology are applied. Remote, solar-powered, seismometer stations continuously record and <br />transmit seismic waves via radio to computers residing on a closed local-area network (LAN). <br />Raw data and/or processed results can then be made available to other networks via controlled <br />access. Networks of this design are readily amenable to expansion by incorporation of additional <br />stations that are accessible via closed LAN, virtual private network (VPN) or public Internet. <br />NIOSH has developed similar distributed seismic acquisition and processing methods (e.g. <br />Swanson et al., 2002) and applied them in mine safety research studies employing high- <br />frequency "microseismic" monitoring. With the larger coverage area of the present network, <br />higher frequencies get attenuated so conventional hardware, with lower data sampling rates, is <br />employed. <br />Seismic Stations: Kinemetrics triaxial <br />EpiSensor strorig-motion accelerometers with <br />Altus K2 data recorders. A fourth channel in <br />the K2 units allows an additional co-located <br />moving-coil seismometer (L4, Sercel Inc) to <br />also be recorded, providing higher sensitivity to <br />smaller and/or more distant seismic events. <br />Sampling rate 100 samples per second. GPS <br />• time synchronization. Local event recording <br />and continuous data streaming. <br />A PP?:w_ D