The material erupting at volcanoes near the Tonga and Fiji islands has flowed many hundreds of miles, originating deep in the earth near the Samoa islands to the north. The work is supported by the National Science Foundation. Smith examined seismic anisotropy, a phenomenon where the velocity of a seismic wave depends on the vibration direction of the wave. This variation in velocity is usually due to the alignment of rock crystal orientations. The flow patterns in the earth align the rock crystals deep in the mantle.
Scientists can thus determine the direction of mantle flow by mapping the anisotropy directions.