Lithospheric and asthenospheric anisotropic gradients along the Eastern North American Margin imaged by frequency dependent quasi-Love wave scattering

Abstract

The eastern North American margin has experienced a wide array of plate-scale tectonic deformational events, including the breakup of Pangaea. The margin may also host complex patterns of active asthenospheric mantle dynamics. Several studies have observed a strong change in anisotropy across the margin that have been interpreted variously as active asthenospheric flow or past lithospheric deformation. Separating these candidate processes has proven difficult. To constrain the likely source of the change in anisotropy across the margin, we examine scattered quasi-Love waves over three frequency ranges with peak sensitivities in the lithosphere (∼75 km), the uppermost mantle (∼150 km), and the asthenosphere (∼250 km). We observe strong quasi-Love wave scattering along the margin in the lowest two frequency bands but far fewer scatterers in the lithosphere-dominated highest frequency band. The clear frequency dependence suggests a change in anisotropy across the margin is likely located in the asthenosphere and related to active mantle dynamics.