Seismic evidence for widespread deep crustal deformation caused by extension in the western US

Laboratory experiments have established that many earth materials are strongly anisotropic. Observations of azimuthal and radial anisotropy in the upper mantle are attributed to the lattice-preferred orientation (LPO) of olivine caused by the shear strains associated with deformation, and provide some of the most direct evidence for deformation and flow within Earth’s interior. Although observations of crustal radial anisotropy would improve understanding of crustal deformation and flow patterns resulting from tectonic processes, large-scale observations have been limited only to regions of particularly thick crust. Here we show that new observations from ambient noise tomography in the western US reveal strong radial anisotropy in the deep (middle to lower) crust confined primarily to the geological provinces that have undergone significant extension during the Cenozoic Era (since ∼65 Ma). The coincidence of crustal radial anisotropy with the extensional provinces of the western US suggests that the radial anisotropy results from the LPO of anisotropic crustal minerals