AN EVALUATION OF A METHOD FOR FOCAL-DEPTH DETERMINATION OF SEISMIC DISTURBANCES FROM UNDERGROUND NUCLEAR EXPLOSIONS.
Special technical rept.,
PENNSYLVANIA STATE UNIV UNIVERSITY PARK DEPT OF GEOLOGY AND GEOPHYSICS
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The Watson-Merdler method for determination of focal depths was applied to fourteen seismograms from underground nuclear explosions. Because the depths for blasts are less than 1 km, the true time delta t for the actual surface reflection was not tested. 200 cases where concentration ratio, C sub R, was greater than in the original seismogram and where the area under the seismogram was reduced were investigated. Causes which can produce simplification are 1 Deconvolution removes the pP sequence from the seismogram. 2 Deconvolution removes PcP or some other sequence other than pP. 3 Deconvolution produces a larger maximum amplitude in the deconvolved seismogram than in the original. 4 Deconvolution diminishes amplitudes on the seismogram. 5 Deconvolution phases random noise so as to add to or subtract from the principal peaks of the seismic pulse. The doublet-function hypothesis for a seismogram is too simple and is therefore unrealistic. The simplicity criterion may identify many pulses in addition to the pP pulse on the seismogram. The Watson-Merdler method does not show promise to distinguish blasts from earthquakes. Author