Low viscosity of the bottom of the Earth's mantle inferred from the analysis of Chandler wobble and tidal deformation

Masao Nakada, Shun ichiro Karato

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

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.

Original languageEnglish
Pages (from-to)68-80
Number of pages13
JournalPhysics of the Earth and Planetary Interiors
Volume192-193
DOIs
Publication statusPublished - Feb 1 2012

Fingerprint

Chandler wobble
D region
Earth mantle
viscosity
mantle
glacial rebound
geodynamics
seismic waves
analysis
temperature gradients
convection
seismic velocity
adjusting
Postglacial
seismic wave
temperature gradient
wave velocity
sensitivity
melt
decay

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

Cite this

Low viscosity of the bottom of the Earth's mantle inferred from the analysis of Chandler wobble and tidal deformation. / Nakada, Masao; Karato, Shun ichiro.

In: Physics of the Earth and Planetary Interiors, Vol. 192-193, 01.02.2012, p. 68-80.

Research output: Contribution to journalArticle

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