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0 Results-General <br />December was the most seismically active month of the quarter. BRL was moving their longwall <br />from the B3 panel to the B4 panel to the northeast during the beginning of December and seismic <br />activity near their mining was low during that month. <br />Results-Magnitudes <br />Forty-three events with sufficient arrivals were located during the fourth quarter. Magnitude <br />assignments from the MSS network were available for only a portion of the events at the date of <br />this report. No events in this general area were located by the National Earthquake Information <br />Center during this quarter. Preliminary analysis of the ground motion recordings do not indicate <br />that any events reached a magnitude threshold of 3.0 during the quarter. Yeh (2006) indicated <br />that "a minimum earthquake magnitude of 4.0 (ML) was required to cause a landslide." <br />Results-Accelerations J/-. <br />Events with intensities from 50 to 150,000 digital counts have been recorded. For the events Itl <br />located, the maximum horizontal component of ground motion recorded was about 0.0045 g.? <br />These results are based on the preliminary analysis of a sample of the data. <br />Yeh (2006) used a horizontal ground acceleration of 0.015g for modeling the effect of a seismic <br />event on the Bruce Park landslide. The seismic factors of safety ranged from 1.0 to 1.03 which <br />indicated about a 3 to 5 percent reduction from the existing stability. Ground motions (including <br />time histories) with average maximum accelerations of over 0.16 g (GEI Consultants, 2002) were <br />used to evaluate the Bruce Park Dam. The dam was judged to be safe under that input of seismic <br />loading. <br />The maximum horizontal component recorded at TCR, the nearest station to the Bruce Park Dam, <br />was 0.00038. <br />NIZ <br />Results-Locations <br />For a selected set of the larger events preliminary locations were calculated. These locations are <br />shown on Figure 2. Though the locations are preliminary and the sample is not exhaustive, three <br />distinct areas of activity are present, one SW of station FGH, one ENE of station FGH and a <br />cluster of events north of station WFW. <br />CONCLUSIONS The seismic network is operational. The seismic activity in the North Fork Valley <br />is being recorded and the largest events are processed in a preliminary fashion. Station delays to <br />account for station elevation differences will be necessary to precisely correlate the events with the <br />mining activity. Measured ground accelerations are lower than those used in the stability analysis <br />for the Bruce Park dam and landslide. <br />References: <br />Brown, Steve, Geotechnical evaluation of mine-induced seismicity on Monument Dam, Delta <br />County, Colorado, 2005, GEI Consultants, Inc., Englewood, Colorado 801121 2005.