A glassy lowermost outer core

作者：Cormier Vernon F^*

来源：Geophysical Journal International, 2009, 179(1): 374-380.

DOI：10.1111/j.1365-246X.2009.04283.x

• Composition of the core
• Elasticity and anelasticity
• High pressure behaviour
• Body waves
• Interface waves
• Surface waves and free oscillations

P>New theories for the viscosity of metallic melts at core pressures and temperatures, together with observations of translational modes of oscillation of Earth's solid inner core, suggest a rapid increase in the dynamic viscosity near the bottom of the liquid outer core. If the viscosity of the lowermost outer core (F region) is sufficiently high, it may be in a glassy state, characterized by a frequency dependent shear modulus and increased viscoselastic attenuation. In testing this hypothesis, the amplitudes of high-frequency PKiKP waves are found to be consistent with an upper bound to shear velocity in the lowermost outer core of 0.5 km s<SU-1</SU at 1 Hz. The fit of a Maxwell rheology to the frequency dependent shear modulus constrained by seismic observations at both low and high-frequency favours a model of the F region as a 400-km-thick chemical boundary layer. This layer has both a higher density and higher viscosity than the bulk of the outer core, with a peak viscosity on the order of 10<SU9</SU Pa s or higher near the inner core boundary. If lateral variations in the F region are confirmed to correlate with lateral variations observed in the structure of the uppermost inner core, they may be used to map differences in the solidification process of the inner core and flow in the lowermost outer core.

• 出版日期2009-10