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Geotechnical Evaluation of Mine-Induced Earthquakes on Bruce Park Dam <br />Bowie Resources, Limited <br />June 2002 <br />comparison of Figures 3.3a through 3.3c to Figures 2.2a through 2.2c, which present the base <br />input motion, the base motion is attenuated as it propagated towards the crest. The <br />predominant frequency of the computed acceleration time history at the crest of the dam has <br />a sharp peak at about 3.5 Hz (period of about 0.29 second), which corresponds to the <br />fundamental frequency of the one-dimensional SHAKE model with degraded modulus at a <br />maximum shear strain of 0.23 percent. The comparison of the input and crest motions <br />illustrates the attenuation of the high frequency (10 to 20 Hz) and slight amplification of the <br />motion near the fundamental frequency of the dam (3.5 Hz). <br />Figure 3.4 presents the results from the pseudo-static slope stability analysis and SHAKE <br />analysis for the selected magnitude 4.2 earthquake event. The solid curve in <br />Figure 3.4 represents variation in the yield acceleration with depth below the crest of the <br />dam. The dashed curve in Figure 3.4 represents variation in the average maximum . <br />acceleration computed from the SHAKE analysis versus depth below the crest of the dam. <br />The yield accelerations are higher than the maximum accelerations computed by the SHAKE <br />analysis throughout the depth of the dam and foundation soils, resulting in zero permanent <br />deformation. Since zero permanent deformation was determined for magnitude 4.2 event, <br />permanent deformations would also be zero for lower magnitude events (2.5, 2, and 1.75). <br />0 <br />0 <br />02-05-22 Geotechnical Evaluation of Stine-Induced Earthquakes <br />GEI Consultants, Inc. 11