Earth and Planetary Science
EPS Near-Surface Geochemistry and Geobiology

Applying novel seismic computations, Barbara Romanowicz's group reveals the presence of low velocity channels at the base of oceanic asthenosphere

Waveform Tomography Reveals Channeled Flow at the Base of the Oceanic Asthenosphere

Applying a new waveform imaging methodology that takes advantage of accurate numerical seismic wavefield computations, Barbara Romanowicz's group has constructed a global shear velocity model in the upper mantle that reveals the presence of low velocity channels at the base of the oceanic asthenosphere. In a paper recently published in Science (http://www.sciencemag.org/content/342/6155/227), graduate student Scott French, former graduate student Vedran Lekic (now assistant professor at the University of Maryland) and Barbara Romanowicz show that these quasi-periodic finger-like structures of wavelength ~2000 km, stretch parallel to the direction of absolute plate motion for thousands of kilometers. Below 400 km depth, velocity structure is organized into fewer, undulating but vertically coherent, low-velocity plume-like features, which appear rooted in the lower mantle. This suggests the presence of a dynamic interplay between plate-driven flow in the low-velocity zone, and active influx of low-rigidity material from deep mantle sources deflected horizontally beneath the moving top boundary layer. Hotspots are not the direct consequence of plumes impinging on the lithosphere