Effects of Explosion Source Parameters on High-Frequency Pg Spectra
- Steven R. Taylor,
- Howard J. Patton and
- Paul G. Richards
Published Online: 18 MAR 2013
Copyright 1991 by the American Geophysical Union.
Explosion Source Phenomenology
How to Cite
Chael, E. P. (1991) Effects of Explosion Source Parameters on High-Frequency Pg Spectra, in Explosion Source Phenomenology (eds S. R. Taylor, H. J. Patton and P. G. Richards), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM065p0211
- Published Online: 18 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900315
Online ISBN: 9781118663820
- Underground nuclear explosions—Detection—Congresses;
Regional Pg arrivals from NTS nuclear tests produce spectra which fall off steeply at frequencies above 5 Hz. At distances of 150 km and greater, the Pg spectra of explosions with magnitudes of 5.6 (ML ) or less drop into ambient noise levels below 40 Hz. Earthquakes with comparable magnitudes generate much stronger high-frequency signals, often above the noise to 50 Hz. The causes of this dramatic contrast between earthquake and explosion spectra in the southwestern U. S. are not well understood. We have examined the dependence of the Pg spectral roll-off on a variety of source parameters for 21 NTS nuclear tests. There are no clear differences in the spectra of tests from Pahute Mesa, Rainier Mesa, or Yucca Flat. The roll-off also does not depend on source magnitude, at least between ML 2.2 and 5.6, except for predictable effects due to corner frequency scaling. Three tests which produced especially steep spectra were fired in dry material well above the water table, and were also characterized by below-average sonic velocities and densities at the shot points. The other 18 tests showed no clear trends with these parameters, however. Our results suggest that it may be possible in some cases to infer properties of the shot medium of a nuclear test, and perhaps the coupling efficiency, from the spectra of Pg arrivals. We see no evidence of any trend between spectral roll-off and test parameters which suggests a way to produce earthquake-like Pg spectra from NTS explosion sources with ML above 3. However, smaller events, which have higher corner frequencies and limited usable bandwidths, may be difficult to discriminate using Pg spectra.