We request for studies of the lateral heterogeneity and anisotropy of the upper-mantle beneath the Pacific Ocean, using a technique which inverts three-component fundamental and higher-mode surface-wave and body-phase waveforms directly for earth structure. We will concentrate our initial work on the western, northern, and northwestern Pacific Ocean basin, accumulating data from the GDSN and WWSSN networks. Our initial observations of waveforms traversing this region show substantial evidence for upper-mantle anisotropy and heterogeneity not easily explained by simple age-dependent models, including a large area of anomalous fast velocities beneath the northwestern Hawaiian Swell and the Shatsky Rise. Preliminary estimates of polarization anisotropy for "normal" paths indicate that SH velocities are everywhere faster than SV velocities at least to the bottom of the low-velocity zone. Experiments with synthetic data demonstrate the ability of our technique to resolve the distribution of anisotropy with depth and the lid/anisotropy tradeoff.
