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Stratification of Seismic Anisotropy Beneath the East-central United States

Deschamps, F ; Lebedev, S ; Meier, T ; Trampert, J

Eos (Washington, D.C.), 2006-12, Vol.87 (52)

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  • Título:
    Stratification of Seismic Anisotropy Beneath the East-central United States
  • Autor: Deschamps, F ; Lebedev, S ; Meier, T ; Trampert, J
  • É parte de: Eos (Washington, D.C.), 2006-12, Vol.87 (52)
  • Notas: SourceType-Scholarly Journals-2
    ObjectType-Conference Paper-1
    content type line 23
    SourceType-Conference Papers & Proceedings-1
    ObjectType-Feature-2
    ObjectType-Article-3
  • Descrição: Azimuthal anisotropy beneath continents has been attributed either to the current strain due to the relative motion of the lithosphere and asthenosphere, or to ancient deformation frozen within the lithosphere. The two scenarios often contrasted as alternative explanations for the observed shear-wave splitting. Here we map the depth distribution of azimuthal anisotropy using array data from the East-central US, and observe two distinct anisotropic layers, with both scenarios of the origin of anisotropy likely to play a role. We measure inter-station dispersion curves of Rayleigh waves using a new implementation of the cross-correlation approach, and obtain phase-velocity curves in a broad period range (10 to 200s). Inverting a collection of 60 measured dispersion curves for azimuthally anisotropic (2psi and 4psi) phase-velocity maps, we observe strong 2psi- anisotropy in two distinct period ranges. Rayleigh waves between 20 and 35s are sensitive to a layer that extends from the lower crust to the shallow lithospheric mantle. In this range, we find anisotropy of ~1% beneath the orogenic Grenville and Appalachian provinces, with the fast-propagation direction parallel to the sutures. In the cratonic lithosphere, west of the Grenville front, anisotropy is weaker (~0.6%) and has different and less coherent fast directions. The Grenville-Appalachian lithospheric anisotropy is likely to be due to the deformation frozen since the ancient orogenies. The observed depth range of this anisotropic layer may reveal the thickness of the deforming lithosphere as it was by the end of the orogenic episodes. In the period range 40-100s anisotropy is weak or absent, but around 140s (sampling the upper asthenosphere) we observe substantial anisotropy ( > 1%) with a laterally uniform fast direction that is parallel to the plate motion. The fast directions of shear- wave-splitting measured in the region are also parallel to the fast direction of 2psi-anisotropy we inferred. Our measurements thus confirm that the splitting here originates mainly within the asthenosphere.
  • Idioma: Inglês
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  • Realização: ABCD-USP USP   Logos de Redes Sociais: Freepik

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