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Determination of intrinsic attenuation in the oceanic lithosphere-asthenosphere system

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Science  22 Dec 2017:
Vol. 358, Issue 6370, pp. 1593-1596
DOI: 10.1126/science.aao3508

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Determining damping of our plates

For plate tectonics to operate, a weaker layer called the asthenosphere must underlie the rigid lithospheric plates. Quantifying the difference in strength comes down to how much each layer attenuates energy. Takeuchi et al. exploited an ocean-bottom seismic network and seismic energy from the 2011 Japanese Tohoku-oki earthquake to quantify the attenuation in each layer (see the Perspective by Dalton). The attenuation of energy in the asthenosphere lined up with previous estimates, but the lithospheric attenuation was roughly one-fifth as strong as that predicted by some previous models.

Science, this issue p. 1593; see also p. 1536

Abstract

We recorded P and S waves traveling through the oceanic lithosphere-asthenosphere system (LAS) using broadband ocean-bottom seismometers in the northwest Pacific, and we quantitatively separated the intrinsic (anelastic) and extrinsic (scattering) attenuation effects on seismic wave propagation to directly infer the thermomechanical properties of the oceanic LAS. The strong intrinsic attenuation in the asthenosphere obtained at higher frequency (~3 hertz) is comparable to that constrained at lower frequency (~100 seconds) by surface waves and suggests frequency-independent anelasticity, whereas the intrinsic attenuation in the lithosphere is frequency dependent. This difference in frequency dependence indicates that the strong and broad peak dissipation recently observed in the laboratory exists only in the asthenosphere and provides new insight into what distinguishes the asthenosphere from the lithosphere.

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