Upper mantle structure of Arctic Canada from Rayleigh wave dispersion

The characteristics of the upper mantle velocity-depth sections also vary significantly. For paths crossing the central-northern mainland and Baffin Island, the Monte-Carlo models give near-constant velocity to at least 240 km depth in the upper mantle. The best match to the dispersion curves can be obtained by the inclusion of a shallower (∼ 200 km depth) low-velocity zone, but this feature is not required to match the data within physically realistic error bounds. In the central Arctic islands, the models show a 'lid' of relatively high velocities in the upper section of the mantle model, underlain by a low-velocity zone. This velocity pattern is consistent with previous interpretations of the character of the seismological lithosphere and asthenosphere. The base of the lid is difficult to identify, but negative velocity gradients are modelled over the ∼ 100-200 km depth range. Along the Sverdrup Basin margins, where the velocity anomalies are smallest, the models are similar in character to the iasp91 reference profile, showing a gradual increase in velocity with depth.