TY - JOUR
T1 - Low viscosity of the bottom of the Earth's mantle inferred from the analysis of Chandler wobble and tidal deformation
AU - Nakada, Masao
AU - Karato, Shun ichiro
N1 - Funding Information:
We thank J. Okuno for computing relative sea-level changes and two anonymous reviewers for their helpful comments. This work was partly supported by the Japanese Ministry of Education, Science and Culture (Grand-in-Aid for Scientific Research No. 22540440 )
PY - 2012/2
Y1 - 2012/2
N2 - Viscosity of the D' layer of the Earth's mantle, the lowermost layer in the Earth's mantle, controls a number of geodynamic processes, but a robust estimate of its viscosity has been hampered by the lack of relevant observations. A commonly used analysis of geophysical signals in terms of heterogeneity in seismic wave velocities suffers from major uncertainties in the velocity-to-density conversion factor, and the glacial rebound observations have little sensitivity to the D' layer viscosity. We show that the decay of Chandler wobble and semi-diurnal to 18.6years tidal deformation combined with the constraints from the postglacial isostatic adjustment observations suggest that the effective viscosity in the bottom ∼300km layer is 10 19-10 20Pas, and also the effective viscosity of the bottom part of the D' layer (∼100km thickness) is less than 10 18Pas. Such a viscosity structure of the D' layer would be a natural consequence of a steep temperature gradient in the D' layer, and will facilitate small scale convection and melt segregation in the D' layer.
AB - Viscosity of the D' layer of the Earth's mantle, the lowermost layer in the Earth's mantle, controls a number of geodynamic processes, but a robust estimate of its viscosity has been hampered by the lack of relevant observations. A commonly used analysis of geophysical signals in terms of heterogeneity in seismic wave velocities suffers from major uncertainties in the velocity-to-density conversion factor, and the glacial rebound observations have little sensitivity to the D' layer viscosity. We show that the decay of Chandler wobble and semi-diurnal to 18.6years tidal deformation combined with the constraints from the postglacial isostatic adjustment observations suggest that the effective viscosity in the bottom ∼300km layer is 10 19-10 20Pas, and also the effective viscosity of the bottom part of the D' layer (∼100km thickness) is less than 10 18Pas. Such a viscosity structure of the D' layer would be a natural consequence of a steep temperature gradient in the D' layer, and will facilitate small scale convection and melt segregation in the D' layer.
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U2 - 10.1016/j.pepi.2011.10.001
DO - 10.1016/j.pepi.2011.10.001
M3 - Article
AN - SCOPUS:84857039979
SN - 0031-9201
VL - 192-193
SP - 68
EP - 80
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
ER -