Earth and Planetary Science
EPS Planetary Science

MAY 2007 - Study reveals two layers of seismic anisotropy beneath North America

In their recently published paper in Nature (reprint), Barbara Romanowicz and Federica Marone present their study of seismic anisotropy beneath the North American continent. Seismic anisotropy provides information about mineral orientations, which, in turn, can be related to flow in the mantle. Their study shows evidence for two layers of anisotropy. At asthenospheric depths, the fast axis is sub-parallel to the plate motion, confirming the presence of shear related to current tectonic processes, whereas within the lithosphere, the orientation is significantly different, indicating that anisotropy at these shallower depths was 'frozen-in' long ago.