A study of short-period S-wave spectra from deep events recorded at LRSM stations indicates severe attenuation of S waves under the Western United States. The average differential in ts* between the Eastern and Western United States was found to be ∼0.67 ± 0.19 sec (95 per cent confidence interval), which is several times greater than Δ tp* ∼ 0.2 - 0.25 for short-period P. This indicates that most, if not all, energy loss occurs in shear deformation. The numerical value of the ts* differential is also smaller than that derived from long-period spectra indicating a frequency dependence of Q.

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