Is inner core translation a good model?

Vernon Cormier, Lizzie Day, Zack Geballe, Marine Lasbleis,

Mohammad Youssof, Han Yue

Does the inner core grows layer by layer?

Does it convect?

Deguen, 2012

Modified from a figure by Jessica Irving

Inner inner core?

EastWest

• FAST isotropic velocity • More attenuating (low Q) • Less anisotropic

• SLOW isotropic velocity•Less attenuation (high Q)• More anisotropic

Summary of seismic features

Waszek & Deuss, JGR, 2012

Hemispheres of P-wave travel time

T-dependent viscoelasticity is not the cause

East

West

8.5 mol % Si< 8.8 mol % Si

Composition is an unlikely cause

Cottaar and Buffet (2012)Alfe et al. (2002)

Translation: a type of convectionSlow Fast

Monnereau et al., Science, 2010

Age distribution in a translating inner core

300 km 500 kmAge (Ma)

0 15075

0 km 100 km

Average age sampled by imaginary seismic data set

Age domain size seismic properties

Model explains the Vp hemispheres!

1 elasticity model fits, 5 do not

Tuned parameter #2: Domains grow to ~ λseismic/2π

Calvet and Margerin, 2008

Q from model < observed Q

Other seismic features

Inner inner core?

EastWest

Modified from a figure by Jessica Irving

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: (1) domains grow to approximately λSeismic/2π , (2) the iron alloy making up the inner core has relatively high

elastic anisotropy