Is the velocity of Pn an indicator of Q|[alpha]|?

IN a recent paper Booth et al.1 showed that short period teleseismic P waves are recorded with relatively small amplitudes at long range seismic measurement (LRSM) stations in the western United States compared with those in the eastern half of the country. This is in agreement with the results of Jordan et al.2 and several more recent studies. Booth concluded that this might be because the upper mantle anelastic quality factor Qa is higher in the east, and consequently waves passing through it suffer less absorption.