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

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Science  05 Sep 2013:
1241514
DOI: 10.1126/science.1241514

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Abstract

Understanding the relationship between different scales of convection that drive plate motions and hotspot volcanism still eludes geophysicists. Using full-waveform seismic tomography, we imaged a pattern of horizontally elongated bands of low shear velocity, most prominent between 200 to 350 km depth, which extends below the well-developed low-velocity zone. These quasiperiodic finger-like structures of wavelength ~2000 km align 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.

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