Long-period multiple S and ScS phases observed in northern Europe were analysed t o determine mantle attenuation in the 0.02 to 0.2 Liz range under the Eurasian shield. Two groups of' events were used: deep Far-Eastern earthquakes and large earthquakes near the edges of the shield areas of Eurasia. The Q of the upper mantle under the Eurasian shield region was estimated in the time domain by taking amplitude ratios and in the frequency domain by taking spectral amplitude ratios among various arrivals. Under shield regions, SS/S amplitude ratios and multiple ScS amplitude ratios give t i -2.5-3.0 s in the 0.02 to 0.20 Hz band. The results show that the uppermantle Q under this shield area is higher than the global average, but less than the Q values inferred from our studies of short-period data in the same area. Preliminary results suggest significantly higher / : under tectonic regions in the same frequency band.

Spectral analysis of P and P coda from NTS explosions recorded at NORSAR shows that magnitudes based on spectral integration of P coda provide a significantly more precise measure of yield than those based on the initial P. Coda amplitudes and spectra are considerably less sensitive to nearsource variations than the direct P. A plot of P-coda magnitude, after correcting for the effects of attenuation in the upper mantle and the source spectrum based on knowledge of approximate yield or mb, versus log yield appears to have a slope of unity. This implies that P coda from several stations (with different but known t* values) can be combined to improve the yield determinations further. Single station P coda from Soviet explosions can also be used to determine relative yields that appear to be at least as precise as those from Lg based on a network of stations.

Justific

No 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.