The attenuation of Pn based on seismic energy density in a three-second time window was examined as a function of frequency in the distance range 204.0 ≦ Δ ≦ 346.4 km for underwater explosions in the Gulf of Maine. The diffracted P wave contained energy in the approximate frequency interval 1.25 to 20 cps and attenuation over this portion of the spectrum exhibited an unusual frequency-dependence with little scatter in the data. Dissipation constants are estimated from these observations. Integration of the extrapolated energy spectrum suggests empirically that the seismic source efficiency is about 8 per cent.

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