Measurement of frequency dependent Lg attenuation in the Great Basin

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(ƒ)=206ƒ0.68 over the band 0.3 ⩽ ƒ ⩽ 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(ƒ) = 214(± 15)ƒ0.54(±0.09), for 0.3 ⩽ ƒ ⩽ 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.