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Geotechnical Evaluation of Mine-induced Earthquakes on Bruce Park Dam <br />Bowie Resources, Limited <br />June 2002 <br />91 <br />single magnitude 4.2 event and a combination of 100 magnitude 1.75 events, 20 magnitude <br />2.0 events, and 5 magnitude 2.5 events. In our opinion, this is a very conservative estimate <br />of potential mine-induced seismicity at the Bruce Park Dam site. <br />2.3 Attenuation Relationship <br />McGarr, et al. (1981) developed an empirical attenuation relationship from data obtained at <br />the East Rand Proprietary Mines in South Africa. The seismic events used in development of <br />this relationship had a ML between 1 and 2.6, hypocentral distances from about 15 to 5,000 <br />feet, and frequencies of several hundred Hertz. Measured peak ground velocities ranged up <br />to 0.2 feet per second (ft/s) and showed a well-defined dependence on earthquake size as <br />measured by ML. The following relationship was proposed based on regression fits to the <br />recorded data; which agrees well for earthquakes of ML up to 6.4: <br />Log (R V) = 3.95 + 0.57 ML <br />0" <br />where, <br />R = distance to event, centimeter (cm) <br />V = peak-particle velocity, centimeter per second (cm/s) <br />ML = local magnitude <br />Using a distance of 0.75 kilometer (km), which is the closest distance from the Bruce Park <br />Dam to the proposed mining activities and the above equation, the computed peak-particle <br />velocities for various magnitudes of mine-induced earthquakes are summarized in Table 2.1. <br />TABLE 2.1 <br />PEAK PARTICLE VELOCITIES FOR VARIOUS MINE-INDUCED EARTHQUAKE <br />MAGNITUDES <br />Earthquake Magnitude, ML Peak Particle Velocity <br />ftls <br />4.2 1.0 <br />2.5 0.1 <br />2.0 0.06 <br />1.75 0.04 <br />C: <br />2.4 Basis for Selected Ground Motion Time History <br />We were unable to obtain digitized time-acceleration records for typical mine-induced <br />ground motions, therefore, we modified an available digitized record of the north-south <br />02-05-22 Geotechnical Evaluation of Mine-Induced Earthquakes <br />GEI Consultants, Inc.