Subseismic description of the Slichter modes in a rotating Earth

Peng, Zhengrong (1990) Subseismic description of the Slichter modes in a rotating Earth. Masters thesis, Memorial University of Newfoundland.

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Abstract

This thesis reports a study of the triplet of (purely translational) Slichter modes of inner core oscillation for a simplified uniformly rotating Earth model with spherical elastic inner core, spherical rigid fixed mantle and neutrally stratified, compressible liquid core. A variational principle is used to solve the subseismic wave equation, which is used to model the liquid core dynamics. The investigation shows the utility of the subseismic wave equation for describing a long-period oscillation, with the effects of higher order harmonics in the displacement field taken into account. For the first time, a numerical estimate of error involved in making the subseismic approximation is given for a particular mode. The eigenperiod of the Slichter mode is found to be around 5 hours for neutrally stratified liquid core with total mass constrained by PREM (1981) data. The effect of the Earth's rotation is to split the mode into a triplet with eigenperiods 12% shorter, 2% shorter, and 10% longer. The effects of compressibility of the liquid core and elasticity of the inner core are to increase the eigenperiod by about 0.6% and 9% respectively. The study can be regarded as a preliminary numerical attempt to describe gravitational/inertial oscillations of the Earth by the subseismic wave equation.

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