Travel-time residuals for teleseismic PP waves reflected under Newfoundland are consistent with a crust towards the western edge of the Central Mobile Belt at least 10 km thicker than in adjacent regions. The thicker and faster crust probably overlies an area of the upper mantle that is up to about 0.5 km s−1 faster than normal for P waves, down to at least 100 km depth. The higher seismic velocities may be due to anisotropy in a former oceanic upper mantle. The low number of reflections observed from the eastern margin of the Mobile Belt could be due to asymmetry in the ray paths due to dipping structure, such as a fossil subduction zone, near the PP reflection point.

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