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Investigating Inner Core Dynamics: Layer Growth, Convection, and Seismic Properties

This study explores the inner core's structural and dynamic characteristics, addressing whether it grows layer by layer and convects. Key seismic features reveal that the inner core exhibits anisotropic properties with variations in velocity and attenuation. The analysis shows a rigid translation model consistent with observed hemispherical variations in seismic velocities. The implications for the composition and elasticity of the inner core materials are discussed, proposing future tests to further understand its complex behavior through textured polycrystalline and different elasticity models.

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Investigating Inner Core Dynamics: Layer Growth, Convection, and Seismic Properties

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  1. Is inner core translation a good model? Vernon Cormier, Lizzie Day, Zack Geballe, Marine Lasbleis, Mohammad Youssof, Han Yue

  2. Does the inner core grows layer by layer? Does it convect? Deguen, 2012

  3. Summary of seismic features • SLOW isotropic velocity • Less attenuation (high Q) • More anisotropic • FAST isotropic velocity • More attenuating (low Q) • Less anisotropic West East Inner inner core? Modified from a figure by Jessica Irving

  4. Hemispheres of P-wave travel time Waszek & Deuss, JGR, 2012

  5. T-dependent viscoelasticity is not the cause East West

  6. Composition is an unlikely cause < 8.8 mol % Si 8.5 mol % Si Cottaar and Buffet (2012) Alfe et al. (2002)

  7. Translation: a type of convection Slow Fast Monnereau et al., Science, 2010

  8. Age distribution in a translatinginnercore 0 km 100 km Age (Ma) 500 km 300 km 0 75 150

  9. Average age sampled by imaginary seismic data set

  10. Age domain size seismicproperties

  11. Model explains the Vphemispheres!

  12. 1 elasticity model fits, 5 do not

  13. Tuned parameter #2: Domains grow to ~ λseismic/2π Calvet and Margerin, 2008

  14. Q from model < observed Q

  15. Other seismic features West East Inner inner core? Modified from a figure by Jessica Irving

  16. Future tests • Try to explain innermost inner core with a textured polycrystalline scattering model • Test a spectrum of iron elasticity models • Map Vp in different frequency bins • Map Q Conclusion: Rigid translation is consistent with observed hemispherical variation in Vp provided that: domains grow to approximately λSeismic/2π , the iron alloy making up the inner core has relatively high elastic anisotropy

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