Numerical seismograms are computed for a compressional pulse in a layered model. The simpler models consist of a fluid layer over a fluid half-space, a fluid layer over a solid half-space, and a solid layer over a solid half-space. Restricted portions of the theoretical response for a layered model approximating the Earth are constructed. Synthetic seismograms are generated using the pressure pulse appropriate for NTS events and the long-period instrument response. The interplay between the PL wave, the refracted wave along the lid, and the arrival from the base of the low-velocity zone is displayed. A detailed comparison between the synthetics and observations indicates a prominent low-velocity zone with appreciable seismic absorption. Observed regional wave-shape characteristics are displayed and a reconnaissance map of lateral variations along the top of the mantle presented.