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Accepted · first revision · record

Title: What produces the inner core's seismic anisotropy and hemispherical asymmetry?
Plain: Seismic waves cross the inner core a few percent faster along Earth's axis than along the equator, and its eastern and western halves look different. The crystal alignment and process behind this are not known.
Precise: Compressional waves travel about 3 percent faster on polar than equatorial paths; velocity, attenuation and anisotropy differ between quasi-eastern and quasi-western hemispheres; an innermost inner core may have a distinct anisotropy axis. Identify the iron phase (hcp or bcc) and the texturing mechanism (solidification texture, Maxwell-stress deformation, translational convection, order-disorder in Fe-Si) that reproduces all three observations. An answer is a dynamical model whose predicted texture matches global travel-time and normal-mode data.
Settled by: A deformation or solidification model with mineral-physics elastic constants that fits global body-wave and normal-mode anisotropy, including the hemispherical pattern.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: (empty)
Posed since: 1986