Lithospheric deformation and mantle dynamics beneath the eastern North American Margin from frequency-dependent shear wave splitting analyses
Date
2023
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Publisher
University of Delaware
Abstract
Constraints on the relative contributions of lithospheric and asthenospheric seismic anisotropy along the eastern passive margin of North America are necessary to further our understanding of past tectonics and current mantle dynamics. Previous studies have invoked several different interpretations of lithospheric and asthenospheric deformation along the margin, including vertical mantle flow, layered anisotropy, or collision-related lithospheric fabrics. The use of frequency-dependent shear wave splitting can help us distinguish between these potential interpretations. Our dataset encompasses the Appalachian Mountains in the west to the Atlantic coast in the east allowing us to investigate lateral changes in anisotropic properties. We measure shear wave splitting of teleseismic core-refracted waves recorded at seismic stations in three different frequency ranges: low (10 – 50 s), mid (5 – 10 s), and high (1 – 5 s). We observe clear frequency dependence in our results with primarily null results in the low frequency and abundant splitting in the mid and the high frequencies. In the mid and high frequencies, splitting does not correlate with plate motion. Our results instead suggest that vertically-varying anisotropy is present along the eastern US with vertical flow in the mantle beneath most of the coastal plain. Systematic back azimuthal dependence of splitting parameters further suggests layered anisotropy. We find that the anisotropic structure changes laterally with a dominantly lithospheric contribution beneath the Appalachians and a primary mantle dynamics control along the coast.
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Keywords
Anisotropy, Deformation, Eastern North America, Shear wave splitting