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• The ground motion is measured in terms of peak particle velocity and is a combination of body and <br />surface waves (Figure 1)~. The body waves attenuate more rapidly with distance from the shot than <br />the surface waves. Body waves spread spherically, whereas the surface waves expand in two <br />dimensions. The principal cause of ground motion attenuation with distance is due to simple <br />geometric spreading. As the ground <br />motion wave train s reads outwards <br />Fi,¢ure 1 -Surface and Body Waves y p g <br />upon the surface, they are converted <br />• to surface waves. Body waves may also be reflected and refracted to the surface to become <br />converted to surface waves. As the surface wave spreads out, the various components of the wave <br />train have different particle motions, travel at different velocities, and have different geometric <br />constraints. <br />Particle velocity has been determined to be the most significant single parameter, in terms of the <br />potential for damage (as opposed to acceleration or displacement). Furthermore, the peak particle <br />velocity found on any of the three geophone channels is the parameter used, rather than the resultant <br />vector sum particle velocity. All research has been done and all regulations have been written in <br />terms of peak particle velocity (PPV). Using the PPV instead of the vector sum allows for easier, <br />more consistent comparison of values. A true resultant velocity could be calculated from the peak <br />measurements for all three components if they occurred at the same instant of time. In addition, <br />there is variability in how different seismograph manufacturers calculate the vector sum. Some <br />actually calculate a pseudo resultant sum. These models take the peak levels on all three channels, <br />regazdless of where they individually occurred in time, to calculate the vector sum. <br />r Rosenthal, M.F., and G.L. Morlock. Blasting Guidance Manual. U.S. Department of the Interior, Office of <br />1 Surface Mining Reclamation and Enforcement, Mazch, 1987, p.l I . <br />Ibid., p. 12. <br />• <br />P <br />from the energy source, the <br />medium's individual particles are set <br />in retrograde elliptical motion about <br />their rest positions. The wave is <br />generated as each particle transmits <br />energy to the next particle. Some <br />energy loss occurs with each <br />transmission of energy from one <br />particle to the next, which is also a <br />cause of ground motion attenuation <br />with distance. The ground motion is <br />a complex wave train consisting of <br />man different wave types (Fi e <br />3 <br />Y ~ <br />2)~. As the bod waves im in e <br />