title: Changes in seismic anisotropy shed light on the nature of the Gutenberg discontinuity.
abstract: The boundary between the lithosphere and asthenosphere is associated with a platewide high-seismic velocity "lid" overlying lowered velocities, consistent with thermal models. Seismic body waves also intermittently detect a sharp velocity reduction at similar depths, the Gutenberg (G) discontinuity, which cannot be explained by temperature alone. We compared an anisotropic tomography model with detections of the G to evaluate their context and relation to the lithosphere-asthenosphere boundary (LAB). We find that the G is primarily associated with vertical changes in azimuthal anisotropy and lies above a thermally controlled LAB, implying that the two are not equivalent interfaces. The origin of the G is a result of frozen-in lithospheric structures, regional compositional variations of the mantle, or dynamically perturbed LAB.
authors.affiliation: Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, 595 Charles Young Drive East, Box 951567, Los Angeles, CA 90095-1567, USA.
authors.forename: Caroline
authors.initials: C
authors.lastname: Beghein
authors.forename: Kaiqing
authors.initials: K
authors.lastname: Yuan
authors.forename: Nicholas
authors.initials: N
authors.lastname: Schmerr
authors.forename: Zheng
authors.initials: Z
authors.lastname: Xing