Heterogeneity and Anisotropy of Earth's Inner Core

Deuss, Arwen

doi:10.1146/annurev-earth-060313-054658

Cited by 101 publications

(105 citation statements)

References 168 publications

(241 reference statements)

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“…For example, core flow models inverted from the geomagnetic secular variation (Holme 2007) show active Atlantic vs. quiet Pacific hemispheres (Amit and Olson 2006;Aubert et al 2013;Gillet et al 2009;Holme and Olsen 2006;Hulot et al 2002). In addition, the seismic velocity, anisotropy, and attenuation of the inner core exhibit an east-west hemispheric dichotomy (Tanaka and Hamaguchi 1997), although these three seismic properties may sample different parts of the inner core (Deuss 2014;Irving and Deuss 2011). Aubert et al (2008) recovered the observed patterns of the paleomagnetic field and the inner core hemispheric dichotomy in the corresponding time-average quantities of their dynamo model.…”

Section: Relevant Observed Planetary Dynamo Propertiesmentioning

confidence: 75%

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Amit

Choblet

Olson

et al. 2015

Prog. in Earth and Planet. Sci.

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Mantle control on planetary dynamos is often studied by imposing heterogeneous core-mantle boundary (CMB) heat flux patterns on the outer boundary of numerical dynamo simulations. These patterns typically enter two main categories: Either they are proportional to seismic tomography models of Earth's lowermost mantle to simulate realistic conditions, or they are represented by single spherical harmonics for fundamental physical understanding. However, in reality the dynamics in the lower mantle is much more complicated and these CMB heat flux models are most likely oversimplified. Here we term alternative any CMB heat flux pattern imposed on numerical dynamos that does not fall into these two categories, and instead attempts to account for additional complexity in the lower mantle. We review papers that attempted to explain various dynamo-related observations by imposing alternative CMB heat flux patterns on their dynamo models. For present-day Earth, the alternative patterns reflect non-thermal contributions to seismic anomalies or sharp features not resolved by global tomography models. Time-dependent mantle convection is invoked for capturing past conditions on Earth's CMB. For Mars, alternative patterns account for localized heating by a giant impact or a mantle plume. Recovered geodynamo-related observations include persistent morphological features of present-day core convection and the geomagnetic field as well as the variability in the geomagnetic reversal frequency over the past several hundred Myr. On Mars the models aim at explaining the demise of the paleodynamo or the hemispheric crustal magnetic dichotomy. We report the main results of these studies, discuss their geophysical implications, and speculate on some future prospects.

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Section: Relevant Observed Planetary Dynamo Propertiesmentioning

confidence: 75%

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Amit

Choblet

Olson

et al. 2015

Prog. in Earth and Planet. Sci.

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“…Seismological studies of the ICB and its inferred characteristics, such as the density jump between the inner and the outer cores, the shear-wave velocity at the top of the inner core, and scattering of seismic energy from small-scale topography at the inner core surface, are important in elucidating the growth mechanism of the inner core and the source of the geodynamo (Souriau 2007;Sumita and Bergman 2009;Deuss 2014;Tkalčić 2015).…”

Section: Introductionmentioning

confidence: 99%

Complex inner core boundary from frequency characteristics of the reflection coefficients of PKiKP waves observed by Hi-net

Tanaka

Tkalčić

2015

Prog. in Earth and Planet. Sci.

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Frequency-dependent reflection coefficients of P waves at the inner core boundary (ICB) are estimated from the spectral ratios of PKiKP and PcP waves observed by the high-sensitivity seismograph network (Hi-net) in Japan. The corresponding PKiKP reflection locations at the ICB are distributed beneath the western Pacific. At frequencies where noise levels are sufficiently low, spectra of reflection coefficients show four distinct sets of characteristics: a flat spectrum, a spectrum with a significant spectral hole at approximately 1 or 3 Hz, a spectrum with a strong peak at approximately 2 or 3 Hz, and a spectrum containing both a sharp peak and a significant hole. The variety in observed spectra suggests complex lateral variations in ICB properties. To explain the measured differences in frequency characteristics of ICB reflection coefficients, we conduct 2D finite difference simulations of seismic wavefields near the ICB. The models tested in our simulations include a liquid layer and a solid layer above the ICB, as well as sinusoidal and spike-shaped ICB topography with varying heights and scale lengths. We find that the existence of a layer above the ICB can be excluded as a possible explanation for the observed spectra. Furthermore, we find that an ICB topographic model with wavelengths and heights of several kilometers is too extreme to explain our measurements. However, restricting the ICB topography to wavelengths and heights of 1.0-1.5 km can explain the observed frequency-related phenomena. The existence of laterally varying topography may be a sign of lateral variations in inner core solidification.

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“…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).…”

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confidence: 99%

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

Denoeud

Ozaki

Benuzzi‐Mounaix

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Investigation of the iron phase diagram under high pressure and temperature is crucial for the determination of the composition of the cores of rocky planets and for better understanding the generation of planetary magnetic fields. Here we present X-ray diffraction results from laser-driven shock-compressed single-crystal and polycrystalline iron, indicating the presence of solid hexagonal close-packed iron up to pressure of at least 170 GPa along the principal Hugoniot, corresponding to a temperature of 4,150 K. This is confirmed by the agreement between the pressure obtained from the measurement of the iron volume in the sample and the inferred shock strength from velocimetry deductions. Results presented in this study are of the first importance regarding pure Fe phase diagram probed under dynamic compression and can be applied to study conditions that are relevant to Earth and super-Earth cores.X-ray diffraction | iron phase diagram | shock-compressed iron | Earth core | dynamic compression

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Heterogeneity and Anisotropy of Earth's Inner Core

Cited by 101 publications

References 168 publications

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Towards more realistic core-mantle boundary heat flux patterns: a source of diversity in planetary dynamos

Complex inner core boundary from frequency characteristics of the reflection coefficients of PKiKP waves observed by Hi-net

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

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