Research

Context

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.

Chandler Wobble, multi periods?

Chandler Wobble observed in time-varying gravity recorded at Strasbourg SG site and in IERS pole coordinates
Chandler Wobble observed in time-varying gravity recorded at Strasbourg SG site and in IERS pole coordinates
Chandler Wobble observed in polar motion from 1846 to 2011 (from IERS)
Chandler Wobble observed in polar motion from 1846 to 2011 (from IERS)

Free Core Nutation Resonance

The Bayesian package for the inversion of the parameters of the FCN resonance is available in the Ressources section.

Free Core Nutation Resonance: Bayesian inversion of the FCN parameters from the combination of 7 SGs gravimetric data
Free Core Nutation Resonance: Bayesian inversion of the FCN parameters from the combination of 7 SGs gravimetric data

Seismic modes

Seismic modes after the 2011 Mw9 Sendai earthquake at Strasbourg (France) Superconducting Gravimeter site
Seismic modes after the 2011 Mw9 Sendai earthquake at Strasbourg (France) Superconducting Gravimeter site
Seismic modes after the 2010 Mw8.8 Chile earthquake at some Superconducting Gravimeter sites
Seismic modes after the 2010 Mw8.8 Chile earthquake at some Superconducting Gravimeter sites
0S2 amplitude spectrum at Strasbourg (France) superconducting gravimeter site after the 2004 Mw9.0 Sumatra-Andaman earthquake
0S2 amplitude spectrum at Strasbourg (France) superconducting gravimeter site after the 2004 Mw9.0 Sumatra-Andaman earthquake
2S1 amplitude spectrum at Strasbourg (France) superconducting gravimeter site after the 2004 Mw9.0 Sumatra-Andaman earthquake
2S1 amplitude spectrum at Strasbourg (France) superconducting gravimeter site after the 2004 Mw9.0 Sumatra-Andaman earthquake
Comparison at Matsushiro (Japan) between the SG and STS1 seismometer records after the 2004 Mw9.0 Sumatra-Andaman earthquake
Comparison at Matsushiro (Japan) between the SG and STS1 seismometer records after the 2004 Mw9.0 Sumatra-Andaman earthquake

Excitation amplitude of the Slichter mode

Excitation amplitude of the Slichter mode for a zonal degree-one pressure flow in the core as function of the characteristic time of the source. Theoretical computation for a PREM-like Earth's model using a Green function formalism
Excitation amplitude of the Slichter mode for a zonal degree-one pressure flow in the core as function of the characteristic time of the source. Theoretical computation for a PREM-like Earth's model using a Green function formalism
Excitation amplitude of the Slichter mode for a zonal degree-one surface load density as function of the characteristic time of the source. Theoretical computation for a PREM-like Earth's model using a Green function formalism
Excitation amplitude of the Slichter mode for a zonal degree-one surface load density as function of the characteristic time of the source. Theoretical computation for a PREM-like Earth's model using a Green function formalism
Seismic excitation amplitude of the Slichter mode at SG sites.  Theoretical computation for a PREM-like Earth's model using a Green function formalism
Seismic excitation amplitude of the Slichter mode at SG sites. Theoretical computation for a PREM-like Earth's model using a Green function formalism