Sharp Sides to the African Superplume

• DOI: 10.1126/science.1070698
• Publication Date: 2002-07-27T09:54:32Z
• Authors: Sidao Ni; Eh Tan; Michael Gurnis; Don Helmberger
• Keywords: 550; 13. Climate action; 01 natural sciences; 0105 earth and related environmental sciences

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.