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Geotechnical Evaluation of Mine-Induced SelsmiDity on Monument Dam <br />Dorsey 8 Whitney, LLP <br />• measurements, which reflects practical detection settings for typical recording instruments. <br />The larger mine-induced earthquakes (M > 2) are generally associated with overburden <br />depths greater than about 1,500 feet. Ellenberger, et al., 2000, in a National Institute for <br />Occupational Safety and Health (NIOSH) study indicates greater likelihood ofmine-induced <br />seismicity if the following conditions are present: Overburden depths greater than 1,000 feet; <br />strong geologic formations in the roof or floor of the mine seam; and an unusually massive <br />rock unit in the main roof. These conditions would therefore associate the likelihood of <br />mine-induced seismicity with higher confining stress at greater depths and a geologic setting <br />that would undergo a more brittle type failure. Ellenberger's study found very few detectable <br />mining-induced seismic events with less than 1,000 feet of overburden depth, and that most <br />of the activity occurs at greater than 1,250 to 1,500 feet of overburden depth. <br />A search of the NEIC USGS Earthquake catalog found 30 earthquakes identified as likely <br />mine-related by the USGS based on a variety of criteria including location within a known <br />mining district and seismic waveform characteristics and recorded within 100 km radius of <br />the dam site from 1980 to present. The North Fork Valley mining district includes 3 mines: <br />West Elk, Bowie, and Oxbow. These records are listed in Table 4.1. One event that <br />occurred on November 5, 2001, and known to be mine-related is also included in Table 4.1. <br /> <br /> <br />TABLE 4.1 <br />MINE-RELATED EARTHQUAKES FROM NEIC CATALOG <br />Year Latitude Longitude Magnitude Distance <br />(km) Depth <br />(km) <br />1984 39.14 -107.39 3.00 29 1 <br />1994 38.93 -107.48 3.10 5 1 <br />1994 38.90 -107.49 2.80 3 1 <br />1995 38.87 -107.45 3.00 2 1 <br />1995 38.88 -107.48 2.90 1 1 <br />2001 38.85 -107.38 3.40 11 1 <br />2002 38.88 -107.39 2.80 6 1 <br />2002 38.85 -107.39 3.10 7 1 <br />2002 38.90 -107.42 2.90 4 1 <br />2002 38.91 -107.42 3.30 5 1 <br />2002 38.91 -107.42 3.60 5 1 <br />2002 38.92 -107.48 3.20 4 1 <br />2002 38.79 -107.41 3.30 11 1 <br />2002 38.90 -107.45 3.10 3 1 <br />2002 38.82 -107.40 2.70 9 1 <br />2003 38.97 -107.40 2.40 11 1 <br />2003 38.81 -107.38 2.90 10 1 <br />2003 38.91 -107.46 3.40 3 1 <br />2004 38.87 -107.35 3.10 10 1 <br />2004 38.85 -107.43 2.20 5 1 <br />GEI <br />13 <br />06035006-03.16 Movummt Dam GmtecM1nicd Evel <br />March 2006 <br />