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.
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
