Two episodes of extension in the West Antarctic Rift System produced the Transantarctic Mountains, deep sedimentary basins in the Ross Sea, and the Adare Trough spreading center. The Adare Basin and Northern Basin are located at the northwesternmost extent of this region of deformation, and are formed in oceanic and continental crust respectively. Their boundary therefore provides an ideal study area for determining the style of extension in these two types of crust, and for understanding the continuity of deformation between portions of crust in the Ross Sea. Sonobuoy data collected during research cruise NBP0701 are processed to provide a crustal velocity structure along seismic lines trending southeast from the Adare Basin to the Northern Basin. Shallow velocities are determined using reflection data. Processing of all nineteen seismic lines will provide a 3D velocity structure for the Adare Basin.