Average surface-wave attenuation coefficient values along with their 95 per cent confidence limits are determined at periods between 15 and 110 sec for paths across the Pacific Ocean. Values for the fundamental Rayleigh-mode decrease from 3.2 × 10−4km−1 at a period of 15 sec to about 0.95 × 10−4km−1 at the longest periods. Love-wave attenuation coefficient values decrease from 3.8 × 10−4km−1 to about 0.95 × 10−4km−1 over the same period range. Although these values are tentatively taken to correspond to the fundamental Love-mode, higher-mode contamination may bias the observed attenuation coefficient values over the short-period portion of the period range. Attenuation coefficient values for both Rayleigh and Love waves are higher than values previously determined for the stable interior of North America over much of the period range between 15 and 40 sec.
Theoretical seismograms were computed and used as an aid in evaluating the effects of continental margin complexities and higher-mode interference on the attenuation coefficient determinations. Results indicate that the relatively large confidence limits for Rayleigh waves, especially at shorter periods, may reflect continental margin complexities. Higher-mode interference in combination with continental margin complexities produce even greater uncertainty in the determination of the attenuation coefficients for Love waves.