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The stratification of seismic azimuthal anisotropy

By Fan-chi Lin, Michael H. Ritzwoller, Yingjie Yang, Morgan P. Moschetti and Matthew J

Abstract

One-sentence summaries Innovations in the observation of broad-band surface waves allow the inference of 3D azimuthal anisotropy within the crust, lithosphere, and asthenosphere beneath the western US at geological length-scales, which provides new constraints on crustal and mantle deformation, crust-mantle coupling, and sub-lithospheric mantle flow. Short to intermediate period (12 to 54 s) Rayleigh wave phase travel times and SKS shear wave splitting measurements observed with the EarthScope USArray in the western US are used to estimate the 3D distribution of azimuthal anisotropy. The inferred stratified model of anisotropy consists of a middle-to-lower crustal layer, a 80 km thick uppermost mantle layer, and a 200 km thick smoothly varying asthenospheric mantle layer. The pattern of crustal anisotropy relates well to major geological provinces but is uncorrelated with anisotropy in the uppermost mantle and asthenosphere. The fast axis directions in the underlying asthenosphere separate coherently into three broad tectonic regions: the tectonically active western US including the Basin and Range Province, the Columbi

Year: 2014
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