HR: 17:46h
AN: CG24A-06    [Abstracts]
TI: Viscosity of Earth's Outer Core
AU: * Smylie, D E
AF: Department of Earth and Space Science and Engineering, York University, 4700 Keele Street,, Toronto, ON M3J 1P3, Canada
AU: Brazhkin, V V
AF: Institute for High Pressure Physics, Russian Academy of Sciences, 142190 Troitsk,, Moscow, Russian Federation
AU: Palmer, A
AF: Sander Geophysics Ltd., 260 Hunt Club Road, Ottawa, ON K2P 1K2, Canada
AB: The viscosity of Earth's outer fluid core has been the subject of a wide range of estimates. Direct observations of its viscosity tend to be much larger than those found from the extrapolation of laboratory high pressure and temperature experiments. The extrapolations characteristically give values near that of liquid iron at atmospheric pressure, while direct observations are generally many orders of magnitude larger. An exception to this dichotomy results from the extrapolation of laboratory measurements by Brazhkin (1998) and Brazhkin and Lyapin (2000) using the Arrhenius activation model. Although this model is widely used on the assumption that the activation volume is independent of pressure, measurements show that it increases strongly with pressure, yielding an estimate of 102 Pa.s at the top of the fluid core and 1011 Pa.s at the bottom. Of course, such extrapolations are subject to large uncertainties. In this paper, we review direct observations of the viscosity, at the top of the outer core from the decay of the Free Core Nutations, which give 2,371± 1,530 Pa.s, and at the bottom from the reduction in splitting of the two equatorial translational modes of oscillation of the solid inner core, which give an average value of 1.247± 0.035× 1011 Pa.s. Encouraged by the closeness of the Arrhenius extrapolation of laboratory measurements to the direct observations, we use a differential form of the Arrhenius activation model to interpolate along the melting curve to find a viscosity profile across the entire outer core.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
SC: Canadian Geophysical Union [CG]
MN: 2009 Joint Assembly