Regional seismograms are dominated by the phases Pn, Pg, Sn, and Lg. More often Sn and Lg are used to infer the attenuation structure of the lithosphere. The seismic phase Sn is a high-frequency shear-wave (typically from 1 to 4 Hz and occasionally higher) that travels in the lithospheric mantle above the negative velocity gradient which usually marks the lithosphere-asthenosphere boundary. Sn has been reported out to distances of 35 (e. g., MOLNAR and OLIVER, 1969; HUESTIS et aI., 1973). Sn arrives as a high-frequency wave train lasting tens of seconds and up to 1 to 2 minutes. Sn velocities...