Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison with seismic models

Daniele Antonangeli (1) , Eiji Ohtani (2)

1 IMPMC - Institut de minéralogie, de physique des matériaux et de cosmochimie
2 Department of Earth and Planetary Materials Science [Sendai]

Determining the sound velocity of iron under extreme thermodynamic conditions is essential for a proper interpretation of seismic observations of the Earth's core but is experimentally challenging. Here, we review techniques and methodologies used to measure sound velocities in metals at megabar pressures, with specific focus on the compressional sound velocity of hexagonal close-packed iron. A critical comparison of literature results, coherently analyzed using consistent metrology (pressure scale, equation of state), allows us to propose reference relations for the pressure and density dependence of the compressional velocity of hexagonal close-packed iron at ambient temperature. This provides a key base line upon which to add complexity, including high-temperature effects, pre-melting effects, effects of nickel and/or light element incorporation, necessary for an accurate comparison with seismic models, and ultimately to constrain Earth's inner core composition.

Mots clés: High pressure; Comparison with seismic models; Sound velocity measurements; hcp-Fe; Extrapolation schemes; Earth's inner core

Domaines: Géophysique [physics.geo-ph]

Daniele Antonangeli, Eiji Ohtani. Sound velocity of hcp-Fe at high pressure: experimental constraints, extrapolations and comparison with seismic models. Progress in Earth and Planetary Science, 2015, 2 (3), pp.1-11. ⟨10.1186/s40645-015-0034-9⟩. ⟨hal-01132950⟩