Abstract

Love wave phase velocity maps provide essential constraints on radial anisotropy and deformation in the crust and upper mantle. However, the phenomenon of overtone interference causes scatter and systematic bias in the velocity measurements and impedes efforts to image small-scale anisotropic variations. We develop an approach for identifying Love wave measurements that are biased by overtone interference, demonstrate its efficacy with EarthScope USArray data, and determine the first earthquake-derived Love wave phase velocity maps for the entire conterminous U.S. in the period range 35-75 s. We show that radial anisotropy in parts of the crust and most of the lithospheric mantle is necessary to reconcile these maps with Rayleigh wave phase velocities. Our results convey the impact and geographic variability of overtone interference, offer an easy-to-implement method to ameliorate this impact, and present high-resolution constraints on radial anisotropy beneath North America.