Regional variation and frequency dependence ofQβin the crust of the United States

Approximate Lg attenuation coefficient values are determined for paths in eastern North America at periods between 2 and 4 sec where no data were previously available. These new data, together with reported values at a period of 1 sec, are consistent with values predicted by a frequency-dependentent Qβ of the crust in which Qβ varies as ω0.2. The new data are inconsistent with values which would be predicted by models having prominent maxima or minima in Qβ−1 within the period range 1 to 5 sec.Lg attenuation coefficients were computed for the frequency-independent crustal Qβ models of Cheng and Mitchell (1981) for the Basin and Range Province and Colorado Plateau of the Western United States. The predicted values at 1 sec for the Colorado Plateau and Basin and Range Province are about twice as large, and three times as large, respectively, as those predicted for the Eastern United States. Recently reported values of Q for 1-sec Lg in those regions are consistent with the attenuation coefficients and Q values of Lg predicted by the Colorado Plateau and Basin and Range Province models. A model with a small degree of frequency dependence of Qβ would be consistent, but is not required by the data.