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 journalArticlepeer-review

32 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 2012

All Science Journal Classification (ASJC) codes

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

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