This study analyzes Rayleigh wave phase velocities from the Ross Sea (RS) region of the West Antarctica rift system, the Transantarctic Mountains (TAMs), and part of East Antarctica (EA). The Transantarctic Mountain Seismic Experiment deployed 41 three-component broadband seismometers, which provide new data for high-resolution two-dimensional maps demonstrating crustal and uppermost mantle seismic velocity anomalies. The short-period (16--25 s) phase velocity maps are consistent with changes in crustal thickness from ~20 km under the RS to ~35 km beneath the TAMs and EA. Long-period (75--175 s) phase velocity maps indicate high mantle velocities beneath EA, low velocity beneath the RS, and a transition between the two between 50 and 150 km inland. The EA phase velocities in the region adjacent to the TAM exhibit a directional pattern consistent with 2 ¿ 1% azimuthal anisotropy with a NE-SW fast direction. The structure of the RS is similar to continental rifting environments elsewhere, with a pronounced low-velocity zone in the ~80--220 km depth range, whereas EA shows a typical continental cratonic structure with high velocities between the 80 and 220 km depth range.