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Near distance and regional surface waves (Love and Rayleigh in the ICEMELT data set) in the period range 5-100 s, make it possible to measure apparent anisotropy ((SH - SV)/SV)*100) with fine vertical details from 1-D models distributed laterally over 500 km distance in Iceland down to 100-200 km depth. These surface waves do not constrain well azimuthal anisotropy, but with shear wave splitting, receiver functions, and upper crustal body-waves anisotropy, combined interpretation can be done.
Crust with emphasis on the volcanic zones: The highest observed anisotropy is in the top 2-3 km of the crust, with both positive and negative sign. In the volcanic rift zones it has high negative value -9% on average, possibly reflecting vertically fractured crust (tectonic fractures and dykes). Under them at about 4 km depth the SV velocity is on average 4% < SH in about 8 km thick layer. A favored explanation is a subhorizontal layer cake of stiff and soft layers, possibly subhorizontal volcanic intrusions below the extrusive upper crust. In the middle lower crust the SV is higher than SH in about 10 km thick layer. Here a subvertical layer cake of stiff and softer layers is favored, consisting possibly of subvertical layered gabbro, or subvertical ultramafic dyke accumulates.
Lithosphere mantle: Relatively small < ±3% anisotropy. This part of the mantle varies in Iceland from 0 to over 70 km in thickness.
Asthenosphere mantle: The anisotropy is a three dimensional structure. It is generally larger in value than in the lithosphere mantle and in the crust, excluding the top 2-3 km layer of the crust. Shear wave splitting has mapped the interesting change of the integrated fast horizontal direction on average ∼N25°W under the Eurasian plate in Iceland and lower in value in the ∼N25°E direction under the North American plate. The fast direction under the Eurasian plate is associated with a LPO induced by larger scale flow field of the North Atlantic upper mantle, but under the American plate the fast direction is induced by differential shear between east-west flow of an asymmetric plume head and the larger scale North Atlantic flow. In about 15 km thick zone in the depth range 50-75 km under the rift zones +8% high anisotropy is reached that is explained as a combination of the LPO mechanism and melt distribution.
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