IGPP Seminar Series

Global anisotropy: Connecting seismic structure to mantle flow

by Mark Panning

Abstract

Seismic tomography has allowed us to image many important features of the mantle, such as slabs reaching the lower mantle, heterogeneity at the core-mantle boundary, and plumes of many shapes and sizes. Until recently, though, most tomographic models focused on isotropic velocity structure. By considering these velocity variations to be primarily thermal effects, isotropic tomography can be considered as a snapshot of the current thermal state of the mantle. However, most mantle minerals have significant elastic anisotropy, and can only be seen as isotropic seismically due to random orientation of crystals on the scale of seismic wavelengths. It is possible, at least in some regimes of the mantle, to orient the materials to produce macroscopically observable anisotropy. Because these preferred orientations are unlikely to be frozen in over geologic time at mantle temperatures, models of anisotropy on a global scale provide an opportunity to directly link the observed seismic structure with the active deformation processes. To this end we have developed a 3D radially anisotropic model of S velocity in the whole mantle. This model can be linked to mantle flow in several regions, from the uppermost to the lowermost mantle, in particular asthenospheric flow below both oceans and continents, mid-ocean ridge feeding flow, as well as boundary layer flow at the core-mantle boundary.
Tuesday, 10 April 2007
3853 Slichter Hall
Refreshments at 3:45 PM
Lecture at 4:00 PM