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Geotechnical Evaluation of Mine-Induced Earthquakes on Bruce Park Dam <br />Bowie Resources, Limited <br />June 2002 <br />component of El Centro (1940) earthquake that was available in the computer program <br />SHAKE. The recorded El Centro motion is presented on Figure 2.1 a. This motion was <br />about 30 seconds long, had a peak ground acceleration of 0.32g, and contained predominant <br />frequencies in the range of 1 to 2 Hz as shown in the acceleration Fourier spectrum of motion <br />presented on Figure 2. lb. The digitized record contained acceleration data points at time <br />steps of 0.02 seconds. Figure 2.1 c shows the corresponding velocity time history. <br />Key parameters for evaluation of permanent embankment and slope deformation are peak <br />velocity and frequency content of the input motion. Therefore, we made the following <br />adjustments to the referenced ground motion record to approximate a typical mine-induced <br />earthquake: <br />• modified the time step from 0.02 sec. to 0.002 sec., which resulted in a motion that <br />was 3 seconds long with predominant frequencies in the range of 10 to 20 Hz. <br />• scaled the earthquake record such that the peak velocity became approximately equal <br />to the peak velocities listed in Table 2.1. <br />The developed input motions in terms of acceleration and velocity time histories and Fourier <br />transform for earthquake magnitudes 4.2, 2.5, 2.0; and 1.75 are presented on Figures 2.2, 2.3, <br />2.4, and 2.5, respectively. <br />OJ <br />I ] <br />02-03-22 Geotechnical Evalu ion of Mine-Induced Earthquakes <br />GEI Consultants, Inc.