Systematic spatial variations of anisotropic characteristics are revealed beneath the eastern U.S. using seismic data recorded between 1988 and 2016 by 785 stations. The resulting fast polarization orientations of the 5613 measurements are generally subparallel to the absolute plate motion (APM) and are inconsistent with the strike of major tectonic features. This inconsistency, together with the results of depth estimation using the spatial coherency of the splitting parameters, suggests a mostly asthenospheric origin of the observed azimuthal anisotropy. The observations can be explained by a combined effect of APM-induced mantle fabric and a flow system deflected horizontally around the edges of the keel of the North American continent. Beneath the southern and northeastern portions of the study area, the E-W keel-deflected flow enhances APM-induced fabric and produces mostly E-W fast orientations with large splitting times, while beneath the southeastern U.S., anisotropy from the N-S oriented flow is weakened by the APM.
B. B. Yang et al., "Seismic Azimuthal Anisotropy Beneath the Eastern United States and its Geodynamic Implications," Geophysical Research Letters, vol. 44, no. 6, pp. 2670-2678, Blackwell Publishing Ltd, Mar 2017.
The definitive version is available at https://doi.org/10.1002/2016GL071227
Geosciences and Geological and Petroleum Engineering
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01 Mar 2017