Seismic response and anisotropy of a model hcp iron inner core

Abstract

A Lincot, R Deguen, Sébastien Merkel, Philippe Cardin To cite this version:A Lincot, R Deguen, Sébastien Merkel, Philippe Cardin. AbstractWe present a framework for simulating the measurement of seismic anisotropy in a model inner core by computing travel time residuals of synthetic seismic rays propagated through the model.The method is first tested on simple inner core structural models consisting of layers with distinct anisotropy, as often proposed in the literature. Those models are not consistent with geodynamics.Hence, we extend the method to a numerically grown inner core composed of ε-Fe with flow generated from an excess of crystallization in the equatorial belt, inducing polycrystalline textures.The global inner core anisotropy is 7 times smaller than that of the single crystal. Compositional stratification amplifies the global anisotropy by 15% while the addition of solidification textures reduces it by a factor of 2. As such, and within the tested geodynamical models, no published elastic model of ε-Fe at inner core conditions allows for reproducing the 3% cylindrical anisotropy reported in seismology publications. In addition, our models demonstrate that additional information such as the depth dependence and the spread of the observed anisotropy is a key for revealing the dynamics and history of the inner core.

The existence of radial anisotropy in Earth's upper inner core revealed from seismic normal mode observations

“…The flow pattern depends on several uncertain parameters, such as the inner core's viscosity, stratification, and the amount of fluid it contains. However, it is possible to generate a texture with the fast direction of hcp crystals aligned along Earth's radius in the upper inner core and along Earth's rotation axis in the deeper inner core [ Yoshida et al , ; Deguen and Cardin , ; Lincot et al , ]. Therefore, by matching the seismic observations to predicted textures, there is potential to better constrain elusive properties of the inner core, such as its viscosity.…”

Multiscale model of global inner‐core anisotropy induced by hcp alloy plasticity

“…More than 300,000 synthetic seismic rays are generated randomly to probe the whole inner core. For each ray, we estimate the normalized seismic travel times residual δ t / t = ( s − s 0 )/ s 0 , where s is the simulated slowness of the seismic ray and s 0 is the slowness of that same ray for an homogeneous and fully isotropic inner core [ Lincot et al , ].…”

Dynamic X-ray diffraction observation of shocked solid iron up to 170 GPa

“…Recent static compression on iron (11) and iron alloys (12) has highlighted the stability of hexagonal-close-packed (hcp) structure under extreme conditions, whereas previous studies investigated the potential stabilization of double hcp (dhcp) or body-centered cubic (bcc) structures under high pressure and temperature (13)(14)(15)(16)(17). However, having an hcp structure under Earth's inner core conditions is mandatory to explain its anisotropic structure observed by seismology (18,19).…”