Two years of funding are requested to support a study of mantle layering using the first-order mantle reverberations recently discovered by Revenaugh and Jordan (1987a). Waves of this type specifically sub-critical reflections from the 400-km and 650-km discontinuities, have been observed as discrete seismic pulses on SH-polarized seismograms following ScSn wavegroups. We propose to compile an extensive set of mantle reverberations from GDSN recordings and to employ this data set: (1) to map regional variations in (a) vertical travel time through three mantle layers (0-400 km, 400-650 km, 650-2890 km), (b) vertical attenuation through two mantle layers (0-650 km, 650-2890 km), and (c) the reflection coefficient of the 650-km discontinuity; (2) to search for additional discontinuities in both the upper and lower mantle; and (3) to investigate the role of incoherent scattering in the apparent attentuation of ScSn waves.
