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t1,f126g. T'he normal aceeleration on the block would be reduced by 0.174 - 0.026 = <br />0.14Rg which is Ixauw the threshold of 0. I GSg, and the block would fall. <br />ft would seem likely that in a fractured cliff'face with steeply dippingjoint planes, <br />some percentage of the blocks would be held purely hr' friction slung the joint surfaces, <br />with normal forces near the threshold value. Vibrations of the magnitude stated in the <br />Revey report arc capable of triggering these blocks to fall, contrary to the conclusions of <br />that report. <br />Revey argues that the magnitude of these equipment generated vibrations are <br />urden of magnitude smaller than natural processes like hwting and cooling. As was <br />shown abuyc, aceelrratiun is the important factor, so Iei's look at the relative <br />accelerations prexluced by cyuipment vibrations and daih~ heating cycles, assuming <br />heating produces displacements 50 times larger than the vibrations. Using the particle <br />velocity of 0.05 in,~s from the example abon•c, particle displacement from vibrations <br />would he 0.05/(22 x I S Hr) - 0.0(x)53 in. or 530 micro inches, in agreement with Revey <br />Pigurrt 5. llu displacement from heating cycles would then be 0.0265 in. or 26,SUU mtcro <br />inches, which is also in good agreement with Revey Figure 5. "this displacement <br />produces a velocity of OA265 in. x 2n x 1/R6400 Nz = 1.9x I O~t~ in/s for the daily cycle, <br />and an acceleration of I. 9x10'° x ?>< x I/R(r1W 112 _ 1.4x 10~ t o in~s2 = 2.74x 10~ ~ ` g. <br />1lterefore, the accelerations generated by hwtine an i coolinb cycles are about ten ordc~ <br />of magnitude smallrr than those induced by equipment vibrations. <br />Clearly, nattual pnxrsses are nut likely to trigger rox:k falls based upon the <br />frictional model, and the conclusions of the Revey report are completely unfounded <br />without a concise statement of the model upon which his conclusions are based. <br />Sincerely, <br />.~~ ~ ~ <br />Gregory U. Lazaear <br />Geophysicist <br />