Elastic Anisotropy of Earth's Inner Core
Anatoly B. Belonoshko,1,2*
Natalia V. Skorodumova,3
Anders Rosengren,2,4
Börje Johansson1,3,5
Earth's solid-iron inner core is elastically anisotropic. Sound waves propagate faster along Earth's spin axis than in the equatorial plane. This anisotropy has previously been explained by a preferred orientation of the iron alloy hexagonal crystals. However, hexagonal iron becomes increasingly isotropic on increasing temperature at pressures of the inner core and is therefore unlikely to cause the anisotropy. An alternative explanation, supported by diamond anvil cell experiments, is that iron adopts a body-centered cubic form in the inner core. We show, by molecular dynamics simulations, that the body-centered cubic iron phase is extremely anisotropic to sound waves despite its high symmetry. Direct simulations of seismic wave propagation reveal an anisotropy of 12%, a value adequate to explain the anisotropy of the inner core.
1 Applied Materials Physics, Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden.
2 Condensed Matter Theory, Department of Theoretical Physics, AlbaNova University Center, Royal Institute of Technology, SE-106 91 Stockholm, Sweden.
3 Condensed Matter Theory Group, Department of Physics, Uppsala University, Uppsala Box 530, Sweden.
4 NORDITA, AlbaNova University Center, SE-106 91 Stockholm, Sweden.
5 School of Physics and Optoelectronic Technology and College of Advanced Science and Technology, Dalian University of Technology, Dalian 116024, China.
* To whom correspondence should be addressed. E-mail: anatoly.belonoshko{at}fysik.uu.se
