The viscosity structure of the D″ layer of the Earth's mantle is inferred from the decay time of the Chandler wobble and semi-diurnal to 18.6 years tidal deformations combined with model viscosity-depth profiles corresponding to a range of temperature-depth models. We use two typical temperature profiles of the D″ layer by considering its dynamic state: (i) bottom thermal boundary layer of the mantle convection (TBL model) and (ii) vigorously small-scale convecting layer (CON model). Three possible models are derived from the comparison between the numerical and observationally inferred decay times of Chandler wobble and tidal deformation. The first and second models are those with a viscosity of ~10 16Pas at the core-mantle boundary. The temperature gradient for the first one, TBL model with a thickness of the D″ layer (L) of ~200km, is nearly constant within the D″ layer. The second one, TBL and CON models with L~300km, requires that the temperature gradient of the lower part (~100km thickness) is larger than that of the upper part. The temperature increases within the D″ layer for these two models are larger than ~1500K. The third model has a constant low viscosity layer (~100km thickness and viscosity smaller than ~10 17Pas) at the bottom of the D″ layer in TBL (L~200 and 300km) and CON (L~300km) models. The temperature increases would be 1000-1600K depending on the viscosity at the top of the D″ layer (10 21-10 22Pas). The heat flows from the core to the mantle for these three models are estimated to be larger than ~5TW. The third model may be preferable after comprehensively taking account of the fitness of the decay time of the Chandler wobble and the tidal deformations for each model.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Physics and Astronomy (miscellaneous)
- Space and Planetary Science