Spectral estimates of teleseismic P-wave attenuation to 15 Hz.

NORESS recordings of nuclear explosions in central Asia (DELTA = 38o) provide new spectral attenuation estimates for frequencies from about 3 to 15 Hz. Two path spectra, representing propagation losses from the Shagan River and Degelen test sites to S Norway, are calculated using the double-averaging technique. Both paths exhibit less attenuation than previously documented for explosions recorded teleseismically at the UKAEA arrays over the 1- to 8-Hz frequency range. The Shagan and Degelen spectra have somewhat different decay rates, perhaps reflecting variations in average source properties. The results also demonstrate that extrapolation of attenuation models obtained from longer period data to shorter periods may not predict the correct spectral levels. Actual high-frequency measurements are needed in order to characterize attenuation behavior at high frequencies. -from Author