Upper Mantle Shear and Compressional Velocity Structure of the Central US Craton: Shear Wave Low-Velocity Zone and Anisotropy

One‐dimensional upper mantle velocity structure is estimated by modeling P, SV and SH body‐waveforms sampling the central United States. The resulting model features a thick mantle lid with a positive velocity gradient. A significant shear wave low‐velocity zone (6% velocity reduction) is required below the lid however the compressional velocities are not reduced. The paths studied lie along the fast axes of teleseismic shear wave splitting measurements and absolute plate motion. We observe splitting of upper mantle refracted shear‐waves, with the transverse component slow relative to the radial component. In order to fit the shear wave arrivals and satisfy teleseismic shear‐wave splitting observations we infer azimuthal anisotropy (maximum 1.6%) distributed throughout the mantle lid and low‐velocity zone, with increasing anisotropy with depth.