Sharp hemisphere boundaries in a translating inner core

Geodynamic models of a convectively translating inner core have recently been proposed that would account for the seismically observed differences in isotropic velocity between the eastern and western hemispheres of the inner core. These models, however, have previously been thought to be incompatible with seismic observations of a 1.5% P wave velocity change occurring over an 800 km wide region at the boundary between hemispheres of the inner core. Here we show that if rigid translation occurs, the age of material in the 100 km below the inner core boundary changes quickly as it crosses the boundary between the western and eastern hemispheres. We then forward model seismic traveltimes to show that the sharp transition in VP between hemispheres may be explained by a random distribution of highly oriented crystalline domains that grow during translation and are composed of material with relatively high elastic anisotropy (up to 12%).

[1]  J. Aubert.  Flow throughout the Earth's core inverted from geomagnetic observations and numerical dynamo models , 2013 .

[2]  Renaud Deguen,et al.  Eccentricity of the geomagnetic dipole caused by lopsided inner core growth , 2012 .

[3]  R. Deguen.  Structure and dynamics of Earth's inner core , 2012 .

[4]  A. Deuss,et al.  Distinct layering in the hemispherical seismic velocity structure of Earth's upper inner core , 2011 .

[5]  A. Deuss,et al.  Reconciling the hemispherical structure of Earth/'s inner core with its super-rotation , 2011 .

[6]  A. Deuss,et al.  Hemispherical structure in inner core velocity anisotropy , 2011 .

[7]  A. J. Abreu,et al.  Grain growth and loss of texture during annealing of alloys, and the translation of Earth’s inner core , 2010 .

[8]  T. Alboussière,et al.  Melting-induced stratification above the Earth’s inner core due to convective translation , 2010, Nature.

[9]  L. Margerin,et al.  Lopsided Growth of Earth's Inner Core , 2010, Science.

[10]  L. Margerin,et al.  Constraints on grain size and stable iron phases in the uppermost inner core from multiple scattering modeling of seismic velocity and attenuation , 2008, 0803.0264.

[11]  V. Cormier.  Texture of the uppermost inner core from forward- and back-scattered seismic waves , 2007 .

[12]  S. Davis,et al.  Origin of the Low Rigidity of the Earth's Inner Core , 2007, Science.

[13]  B. Romanowicz,et al.  Hemispherical transition of seismic attenuation at the top of the earth's inner core , 2004 .

[14]  Xu Li,et al.  Frequency-dependent seismic attenuation in the inner core. 2. A scattering and fabric interpretation , 2002 .

[15]  L. Wen,et al.  Seismic velocity and attenuation structures in the top of the Earth's inner core , 2002 .

[16]  A. Dziewoński,et al.  The innermost inner core of the earth: Evidence for a change in anisotropic behavior at the radius of about 300 km , 2002, Proceedings of the National Academy of Sciences of the United States of America.

[17]  L. Wen,et al.  Hemispherical variations in seismic velocity at the top of the Earth's inner core , 2001, Nature.

[18]  Douglas A. Wiens,et al.  An empirical relationship between seismic attenuation and velocity anomalies in the upper mantle , 2000 .

[19]  S. Karato.  Seismic anisotropy of the Earth's inner core resulting from flow induced by Maxwell stresses , 1999, Nature.

[20]  H. Hamaguchi,et al.  Degree one heterogeneity and hemispherical variation of anisotropy in the inner core from PKP(BC)–PKP(DF) times , 1997 .

[21]  G. Glatzmaier,et al.  A three-dimensional convective dynamo solution with rotating and finitely conducting inner core and mantle , 1995 .

[22]  B. Buffett,et al.  The strength and efficiency of thermal and compositional convection in the geodynamo , 1995 .

[23]  P. Machetel,et al.  Convection within the inner‐core and thermal implications , 1992 .

[24]  Domenico Giardini,et al.  Evidence for inner core anisotropy from free oscillations , 1986 .

[25]  Andrea Morelli,et al.  Anisotropy of the inner core inferred from PKIKP travel times , 1986 .

[26]  I. Sumita,et al.  Inner core dynamics , 2022, Earth's Core.

[27]  I. Sumita.  8.10 – Inner-Core Dynamics , 2007 .

[28]  Raymond Jeanloz,et al.  Convection and anisotropy of the inner core , 1988 .