Low velocity channels in the oceanic asthenosphere from full waveform inversion using the Spectral Element Method

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Science, 11 October 2013, Vol. 342, pp. 227-230

Scott French, Vedran Lekic, Barbara Romanowicz

Abstract:

Understanding the relationship between different scales of convection that drive plate motions and hotspot volcanism still eludes
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3D view of seismic shear-wave velocity anomalies in the upper 1000 km of the earth's mantle beneath the central Pacific, showing the relationship between the seismically-slow "plumes" and channels imaged in the study. Green cones at the surface correspond to the locations of ocean islands associated with "hot-spot" volcanism (e.g. Hawaii).
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A map view of seismic shear-wave speed in the earth's upper mantle, highlighting the slow wave-speed channels (warm colors) imaged in this study. Where present, the channels align with the direction of tectonic-plate motion (dashed lines).
geophysicists. Using full-waveform seismic tomography, we imaged a pattern of horizontally elongated bands of low shear velocity, most prominent between 200 and 350 kilometers depth, which extends below the well-developed low-velocity zone.These quasi-periodic fingerlike structures of wavelength ~2000 kilometers align parallel to the direction of absolute plate motion for thousands of kilometers. Below 400 kilometers depth, velocity structure is organized into fewer, undulating but vertically coherent, low-velocity plumelike 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.


Click here to learn more about the SEMum2 Model, a global radially anisotropic shear-velocity model of the earth's upper mantle and transition zone.


See related papers:

Lekic, V. and B. Romanowicz (2011) Inferring mantle structure by full waveform tomography using the Spectral Element Method, Geophys. J. Int., 185, 799-831, doi:10.1111/j.1365-246X.2011.04969.x.

Lekic, V. and B. Romanowicz (2011) Tectonic regionalization without a priori information: a cluster analysis of upper mantle tomography, Earth Planet. Sci. Lett., 308, 151-160. doi:10.1016/j.epsl.2011.05.050.



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