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<br />6.5 Hz <br />0 <br /> <br />.001 Log(f) MI OJ - <br />Figure 1 - Amplitude spectrum of vibrations generated at the Benson quarry 0.67 mile <br />away during ripping of bedrock. The peak frequency is at about 6.5 Hz and is about 100 <br />to 1000 times larger than the background amplitudes. The high frequencies roll off above <br />10 Hz due to a high-cut filter with slope of 20 db/octave out to the Nyquist frequency of <br />25 hz. <br />0000 _ ----- -- - <br />4 Hz <br />T ?l resonance <br />--------------- <br />1000 - :------ <br />loo ' ....................... :-..----T --- <br />.001 LogM Ot 0.1 1.0 10 <br />Figure 2 - Amplitude spectrum of vibrations generated at the Benson quarry 0.67 mile <br />away when only the crusher is operating (no ripping). Note the very different character of <br />the spectrum and the strong resonance at a frequency of 4 Hz. This corresponds to the <br />fundamental mode of a standing wave between the crusher and the cliff face.