CNRS researcher

Keywords of research activity: Time-varying Gravimetry, Superconducting Gravimetry, Earth's normal modes, Gravito-elasticity of the Earth, Geodesy

Qu'est-ce que la gravité ?

Newton, Lettre III (25 février 1692-1693), ibid., p. 211, extrait d'une lettre au révérend Dr Bentley :

"Il est inconcevable que la matière brute inanimée, sans la médiation de quelque chose d'autre qui n'est pas matériel, puisse agir sur une autre matière et l'affecter sans contact mutuel, comme cela devrait être si la gravitation, dans le sens d'Epicure, lui était essentielle et inhérente."

Gravité quantique :

Le graviton est le médiateur des ondes gravitationnelles, comme le photon pour les ondes électromagnétiques. 

Relativité générale (Einstein, 1915) :

La gravité est la manifestation de la courbure de l'espace-temps.

Some current and past projects  Geodesy and geophysics

Geocenter motion = motion of center of mass of the entire Earth (solid Earth and surficial layers) with respect to the center of the terrestrial reference frame

  • Characterization of fluid core and inner core dynamics processes from ground and space observations and theoretical modeling
    1. Free Core Nutation (retrograde 430-day nutation in space, quasi-diurnal wobble on Earth)
    2. Free Inner Core Nutation (prograde nutation in space, nearly-diurnal wobble on Earth)
    3. Translational oscillation of the inner core at a 5-hour period ("Slichter" modes)
    4. Interannual & decadal fluctuations from space gravimetry (Hugo Lecomte's PhD thesis 2020-2023)

    Free Core Nutation (FCN) = rotational normal mode of the Earth that exists because of the presence of the elliptical fluid core. The axis of rotation of the flattened fluid core is misaligned with the rotation axis of the Earth's mantle. Displaced flows act as a restoring pressure torque on the fluid core. In a terrestrial reference frame, the FCN mode has a period close to one day, so it is also called "nearly-diurnal free wobble". In a celestial reference frame, its period is about -430 days with a retrograde motion (opposite to Earth's rotation). This mode can be observed by the resonance effect in diurnal tidal waves or in nutation observed by VLBI (Very Long Baseline Interferometry) technique.

    Free Inner Core Nutation (FICN) = equivalent to the FCN but for the solid elliptical inner core. This rotational mode has never been directly observed. The theoretically predicted period is poorly constrained with values ranging from 200 to more than 1000 sidereal days. The IERS Conventions based on VLBI nutation propose a period between 930 and 1140 days.

    • Gravity disturbances at various time and space scales (analysis of gravimeter and tiltmeter records)
    • Seismic modes : Low-frequency seismic modes  after the 2004 Mw9.2 Sumatra-Andaman, 2010 Mw8.8 Chile and 2011 Mw9 Tohoku earthquakes

     

    Interdisciplinarity  Gravitational waves and geophysics

    • Interactions of Gravitational Waves with the Earth
      1. Excitation of seismic modes (J. Majstorovic's PhD thesis 2016-2019)
      2. Perturbation of the Earth's rotation
    • Newtonian noise on instruments
      1. Observed vs. instrumental noise levels of Superconducting Gravimeters
      2. Surficial layers (atmospheric, oceanic, hydrologic) Newtonian and loading deformation contributions on gravity field measurements

    Partnership in French Projets Investissement d'Avenir

    • RESIF : Réseau sismologique et géodésique Français
    • MIGA : Antenne gravitationnelle basée sur l'interférométrie atomique