Measurement of the spatial decay of spectral amplitudes of the higher-mode seismic surface wave train Lg indicates that in the Great Basin the apparent seismic quality factor, Q, is a function of frequency. Observations along a 300 km profile recording of a nuclear explosion yield the function Q(f)=206f0.68 over the band 0.3≤f≤10.0 Hz. Similar analysis using numerous recordings of earthquakes along paths which provide a good average sampling of the Great Basin crust gives Q(f)= 214(¿15)f0.54(¿0.09), for 0.3≤f≤5.0 Hz. If the crustal sampling by Lg energy from nuclear explosions (surface sources) is primarily in the shallow crust, as has been suggested, then these results indicate a greater frequency dependence of apparent Q there than at depth.