Open AccessObservations of pP in the Short‐Period Phases of NTS Explosions Recorded at Norway
Author(s) -
Frasier C. W.
Publication year - 1972
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1972.tb02361.x
Subject(s) - seismogram , geology , seismology , overburden , seismometer , attenuation , deconvolution , seismic wave , test site , displacement (psychology) , period (music) , microseism , p wave , nuclear explosion , geodesy , geotechnical engineering , optics , physics , medicine , psychology , cardiology , psychotherapist , atrial fibrillation , acoustics , nuclear physics
SummaryP waves from 11 Nevada Test Site explosions, recorded digitally at Norway, are examined for pP phases. Rather than using spectral techniques, the combined effect of the short‐period displacement response of the seismometers and Earth attenuation for t *= 0.25 is deconvolved in the time domain from the observed P waves. Each reduced seismogram is interpreted directly as the effective far‐field displacement source for each explosion. The P and pP phases are sharpened by the deconvolution so that pP – P times are more easily picked. These delay times are combined with another set of delay times computed by Kulhánek using spectral methods. Average overburden compressional velocities from the combined set of data shown an increase from 1.5 to 2.5 km s ‐1 from depths of 600 to 1400 m at Pahute Mesa. Data from Yucca Flat and Hot Creek Valley are not complete enough to detect a trend. Calculated velocities are most likely lower than expected due to the fracturing of the overburden section by the explosions. The reduced seismograms show that pP is often smaller in amplitude than P and less rich in high frequencies. A later pulse, possibly due to the slapdown of surface rocks after the spall, is observed to have the same polarity as P . Such effects require more complicated explosion source models than currently being used for short‐period data.