title: Sharp sides to the African superplume.
abstract: Beneath southern Africa is a large structure about 1200 kilometers across and extending obliquely 1500 kilometers upward from the core-mantle boundary with a shear velocity reduction of about 3%. Using a fortuitous set of SKS phases that travel along its eastern side, we show that the boundary of the anomaly appears to be sharp, with a width less than 50 kilometers, and is tilted outward from its center. Dynamic models that fit the seismic constraints have a dense chemical layer within an upwardly flowing thermal structure. The tilt suggests that the layer is dynamically unstable on geological time scales.
authors.affiliation: Seismological Laboratory, California Institute of Technology, Pasadena, CA 91125, USA. stone@gps.caltech.edu
authors.forename: Sidao
authors.initials: S
authors.lastname: Ni
authors.forename: Eh
authors.initials: E
authors.lastname: Tan
authors.forename: Michael
authors.initials: M
authors.lastname: Gurnis
authors.forename: Don
authors.initials: D
authors.lastname: Helmberger