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

Morgan Moschetti and colleagues use ambient noise tomography data from the western United States to show that strong radial seismic anisotropy exists in the deep crust, confined mainly to the geological provinces that have undergone significant extension during the Cenozoic era, since about 65 million years ago. The coincidence of crustal radial anisotropy with these extensional provinces supports the hypothesis that the deep crust within these regions has undergone widespread and relatively uniform strain in response to crustal thinning and extension.