New constraints on the arctic crust and uppermost mantle : surface wave group velocities , P n , and S n

We present the results of a study of surface wave dispersion across the Arctic region (>60◦N) and compare the estimating group velocity maps with new maps of the body wave phases Pn and Sn. Data recorded at about 250 broadband digital stations from several global and regional networks were used to obtain Rayleigh and Love wave group velocity measurements following more than 1100 events with magnitudes Ms > 5.0 that occurred in the northern hemisphere from 1977 to 1998. These measurements were used to construct both isotropic and 2Ψ azimuthally anisotropic group velocity maps from 15 to 200 s period. As elsewhere in the world, the observed maps display the signatures of sedimentary and oceanic basins, crustal thickness variations, and upper mantle anomalies under both continents and oceans. We also present Pn and Sn maps produced from a groomed data set of travel times from the ISC and NEIC bulletins. The long period group velocity maps correlate well with Pn and Sn velocities. Finally, at long wavelengths, the estimated 2Ψ azimuthal anisotropy in Rayleigh wave group velocity correlates well with the azimuthal anisotropy in phase velocity obtained in a global scale study of Trampert and Woodhouse. Because attempts to improve the resolution to regional scales change both the amplitude and the pattern of the inferred azimuthal anisotropy, caution should be exercised in interpreting the anisotropy maps. © 2001 Elsevier Science B.V. All rights reserved.