The Slichter modes in a realistic Earth model

Abstract

The density contrast across the inner core boundary is a critical parameter for evahiating the gravitational energy released from the segregation of the core material upon its cooling and solidification, a process which is one of the main contenders for the source of power of the geodynamo action in the Earth's fluid core. However, the density jump at the inner core boundary has so far not been well determined by conventional short-period seismology, [t is known that the eigenperiods of the (not yet detected) Slichter modes critically depend on this density difference. The Slichter modes are the triplet of degree 1 long-period free oscillations of the Earth which involve translational vibration of the solid inner core in the surrounding liquid outer core. In this thesis, the eigenperiods of the Slichter modes for a realistic Earth model are computed by a variational principle based on the subseismic approximation and by a Galerkin method based on the two potential description of core dynamics. In this study, I have taken into account: (1) elastic deformation of the mantle and inner core, connected to liquid core dynamics via frequency-dependent Internal load Love numbers; (2) retention of the self coupling of the displacement field in the solid parts of the Earth, and the Coriolus coupling up to degree 7 in the liquid core so as to ensure convergence; (3) elliptical stratification of the inner and outer cores (but not the mantle); (4) effects of a mushy inner core boundary. The research is a more comprehensive study of the Slichter oscillation than any previously undertaken, and is aimed to provide theoretical references for helping to determine the density contrast across the inner core boundary.