Abstract

Spectra of teleseismic, short-period P waves from nuclear explosions show clear, path-related differences in their high-frequency falloff rates. P waves from Kazakh explosions commonly show significant seismic energy above the frequency of 5 Hz when recorded in shield regions. Peaceful nuclear explosions in the tectonically stable areas of the USSR have similar properties, together with the Amchitka explosions and SALMON. Nuclear explosions in the Western United States, Algeria, and French Polynesia show much less high frequency energy in their P-wave spectra, and signal energy above 5 Hz is usually not seen. We attribute these variations to lateral changes in the anelastic attenuation properties of the upper mantle. For the events in the contiguous United States, this interpretation is confirmed by the results of reciprocal measurements of Q. About 500 P-wave spectra, not including those utilized in the reciprocal measurements, were used to estimate the contribution to

tp
of the upper mantle Q structures under a number of nuclear test sites and observatories.

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