Defining the elastic properties of the Earth's inner core: Bridging quantum mechanical calculations together with seismic data

Maurizio Mattesini

Departamento de Física de la Tierra, Astronomía y Astrofísica I, Universidad Complutense de Madrid, E-28040 Madrid, Spain
and
Instituto de Geociencias (UCM-CSIC), Facultad de Ciencias Físicas, Plaza de Ciencias 1.
E-28040 Madrid, Spain

It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves travelling ~3% faster along polar paths than along equatorial directions. However, hemispherical anisotropic patterns of solid Earth's inner core (EIC) are rather complex, and the commonly used hexagonal-close-packed (hcp) iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice preferred orientation of a body-centered-cubic iron aggregate (bcc), having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is a compelling evidence for the presence of a body-centered-cubic Fe phase at the top 100 km of the Earth's inner core. The proposed procedure puts novel constraints on the elastic properties of the EIC material and provides a more severe way to guarantee the uniqueness of the achieved results.