TY - JOUR
T1 - Heterogeneity and anisotropy of Earth's inner core
AU - Deuss, Arwen
PY - 2014/1/28
Y1 - 2014/1/28
N2 - Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to alignment of hcp (hexagonal close-packed) iron crystals, aligned either during solidification or by deformation afterward. The existence of hemispherical variations used to be controversial, but there is now strong evidence from both seismic body wave and normal mode observations, showing stronger anisotropy, less attenuation, and a lower isotropic velocity in the western hemisphere. Two mechanisms have been proposed to explain the hemispherical pattern: either (a) inner core translation, wherein one hemisphere is melting and the other is solidifying, or (b) thermochemical convection in the outer core, leading to different solidification conditions at the inner core boundary. Neither is (yet) able to explain all seismically observed features, and a combination of different mechanisms is probably required.
AB - Seismic observations provide strong evidence that Earth's inner core is anisotropic, with larger velocity in the polar than in the equatorial direction. The top 60-80 km of the inner core is isotropic; evidence for an innermost inner core is less compelling. The anisotropy is most likely due to alignment of hcp (hexagonal close-packed) iron crystals, aligned either during solidification or by deformation afterward. The existence of hemispherical variations used to be controversial, but there is now strong evidence from both seismic body wave and normal mode observations, showing stronger anisotropy, less attenuation, and a lower isotropic velocity in the western hemisphere. Two mechanisms have been proposed to explain the hemispherical pattern: either (a) inner core translation, wherein one hemisphere is melting and the other is solidifying, or (b) thermochemical convection in the outer core, leading to different solidification conditions at the inner core boundary. Neither is (yet) able to explain all seismically observed features, and a combination of different mechanisms is probably required.
KW - Body waves
KW - Dynamics
KW - Free oscillations
KW - Iron
KW - Mineralogy
KW - Seismology
KW - Solidification
UR - http://www.scopus.com/inward/record.url?scp=84902176013&partnerID=8YFLogxK
U2 - 10.1146/annurev-earth-060313-054658
DO - 10.1146/annurev-earth-060313-054658
M3 - Article
AN - SCOPUS:84902176013
SN - 0084-6597
VL - 42
SP - 103
EP - 126
JO - Annual Review of Earth and Planetary Sciences
JF - Annual Review of Earth and Planetary Sciences
ER -