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Download PhD thesis (14 Mo)
Seismology has enabled the development of various density models of the Earth’s interior (for instance PREM model, Dziewonski and Anderson, 1981). However the density is still poorly constrained in the lower mantle and inside the core. The density models can be determined using surface observations of seismic waves or the free oscillations of the Earth. These normal modes give us a direct image of the density structure inside the Earth. The seismic modes, excited by a strong earthquake, constrain the density through their frequencies. Their damping constrains the dissipation (anelasticity) inside the Earth. The translational modes of the inner core, the so-called Slichter triplet (Slichter, 1961), are fed back by buoyancy forces so their period is directly linked to the density jump at the inner core boundary (ICB). Besides it constraints the viscosity and the stratification of the liquid outer core at ICB. The density jump at ICB is a key parameter to quantify the energy necessary to maintain the geodynamo process through the compositional convection in the fluid outer core associated with the growth of the inner core (=> age of the inner core). Free core nutation (FCN) is a rotational normal mode of the Earth that exists because of the presence of a fluid core inside the visco-elastic mantle. The period and Q of the FCN can be interpreted in terms of dissipative torques at the core boundaries (electromagnetism and viscosity). The Chandler Wobble is a rotational mode of the Earth which can be seen as the wobble of the rotation axis of the mantle around the main inertia axis of the Earth. The period of the CW is mostly determined by the dynamic flattening of the Earth and the equatorial momentum of the mantle. The oceans, anelasticity of the mantle and the core-mantle coupling contribute to the damping of this oscillation.
