Anisotropy of the Uppermost Mantle in Europe as Obtained from Surface Wave Data
A new approach is proposed to study radial anisotropy of the upper mantle under the European continent. Unlike the methods used so far, we propose to interchange the order of inversion procedures. At the first stage the path-averaged velocity sections of the SH and SV waves are constructed on each path and the path-average anisotropy coefficient is calculated from these sections at different depths. At the second stage the anisotropy coefficients for individual paths are used as initial data in the tomography procedure. This approach excludes different smoothness of Rayleigh and love wave velocities, which leads to significant errors in the estimation of the anisotropy coefficient obtained from the results of SV and SH velocity tomography. The method was applied to the group velocity dispersion data of Rayleigh and Love waves from both earthquake records and ambient seismic noise along the paths crossing the European continent. The results are presented as maps of anisotropy coefficient in three 20 km layers under the Moho boundary. It was found that in the central part of the study area the anisotropy coefficient is either close to zero or characterized by small negative values (about −1%). The values of the anisotropy coefficient decrease with depth. In the sea and coastal areas, the anisotropy coefficient is positive and its values are close to those of the oceanic mantle. The causes for exceeding the velocity of SV waves with respect to the velocities of SH in the continental mantle are discussed.
KeywordsAnisotropy Upper mantle Europe Surface wave tomography
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