Laserfiche WebLink
Geotechnical Evaluation of Mine-Induced Earthquakes on Bruce Park Dam <br />Bowie Resources, Limited <br />June 2002 <br />Section 2 -Seismic Loading <br />2.1 General <br />Seismic events induced by long wall coal mining can typically be caused by roof collapses, <br />rockbursts, and mine collapses. Mine-induced seismic events generally associated with long <br />wall mining tend to have durations of 2 to 3 seconds and frequencies greater than 10 Hz <br />(periods less than 0.1 second). Peaks in seismic activity are generally concurrent with a peak <br />in mining production (extraction) (Arabasz, et al., 1997). Typically, mine-induced <br />earthquakes have Richter local magnitude (ML) 4 or smaller, and occasionally up to ML 5. <br />Seismic events caused by natural tectonic movements, which occur due to a slip of earth's <br />crust along a fault typically produce shaking that may last for seconds to minutes with a <br />predominant frequency content between 0.5 and 5 Hz (predominant period between 0.2 to 2 <br />seconds). The estimated maximum credible earthquake (MCE) for this area of Colorado is <br />ML 5.5 to 6.5 (Kirkham and Rogers, 1981). <br />10 The largest recorded natural earthquake in the United States was a moment magnitude (Mw) <br />9.2 in Alaska in 1964 and the largest recorded mine-induced seismic event in the United <br />States appears to be a body wave magnitude NO 5.3 in the Green River Basin near Rock <br />Springs, Wyoming caused by a catastrophic roof collapse in an underground trona mine <br />(USGS, 2002). <br />2.2 Basis of Selected Ground Motion Magnitudes <br />The database of information on mine-induced seismicity is relatively small. Most of the data <br />available on mine-induced seismicity in the United States is from the Book Cliffs area of <br />Utah and the eastern Wasatch Plateau in the northwest corner of the Colorado Plateau <br />because this is an area that consistently has a high incidence of mine-induced seismic <br />activity. One of the largest events recorded in the Book Cliffs area was a ML 4.2 seismic <br />event in March 2000 (Ellenberger, et. at., 2001), which was related to long wall mining. <br />The available literature indicates that mine-induced earthquakes are typically magnitude 2.5 <br />or lower, and magnitude 1.75 appears to be the lowest limit (threshold) of reliable <br />measurements. <br />For the purpose of the analysis, we considered that the proposed mining activity will take <br />place over a period of 2 years, and permanent deformations were calculated considering a <br />02-05 -22 Geotechnical E,aluation of Mine-Induced Eanhquakes <br />GEI Consultants, Inc. 4