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Title: Hemispherical anisotropic patterns of the Earth's inner core
Authors: Maurizio Mattesinia, Anatoly B. Belonoshkob, Elisa Buforna, María Ramíreza, Sergei I. Simakc, Agustín Udíasa, Ho-Kwang Maod, and Rajeev Ahuja

It has been shown that the Earth's inner core has an axisymmetric anisotropic structure with seismic waves travelling ~3% faster along polar paths than along equatorial directions. Hemispherical anisotropic patterns of the solid Earth's core are rather complex, and the commonly used hexagonal-close-packed iron phase might be insufficient to account for seismological observations. We show that the data we collected are in good agreement with the presence of two anisotropically specular east and west core hemispheres. The detected travel-time anomalies can only be disclosed by a lattice-preferred orientation of a body-centred-cubic iron aggregate, having a fraction of their [111] crystal axes parallel to the Earth's rotation axis. This is compelling evidence for the presence of a body-centred-cubic Fe phase at the top of the Earth's inner core.

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The small number of anti-neutrinos detected at Borexino, only a couple each month, helps to settle a long-standing question among geophysicists and geologists about whether our planet harbours a huge, natural nuclear reactor at its core. Based on the unprecedently clear geo anti-neutrino data, the answer is no, say the UMass Amherst physicists
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De la tectonique dans la graine du noyau
La graine du noyau de la Terre est l'objet le plus caché de notre planète et son investigation est particulièrement difficile. Il y a plus d'une vingtaine d'années, les sismologues en ont révélé une propriété marquante, une anisotropie vis-à-vis des ondes sismiques. Les spécialistes du noyau cherchent depuis à en comprendre les causes. Dans une publication qui vient de paraître dans la revue Nature Geoscience, des géophysiciens du Laboratoire de géophysique interne et tectonophysique de Grenoble (INSU-CNRS, Université Joseph Fourier), proposent un modèle de cristallisation de la graine évoluant au cours du temps pour en expliquer la structure.

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It's a classic image from every youngster's science textbook: a cutaway image of Earth's interior. The brown crust is paper-thin; the warm mantle orange, the seething liquid of the outer core yellow, and at the center the core, a ball of solid, red-hot iron.
Now a new theory aims to rewrite it all by proposing the seemingly impossible: Earth has not one but two inner cores.
The idea stems from an ancient, cataclysmic collision that scientists believe occurred when a Mars-sized object (Theia) hit Earth about 4.45 billion years ago. The young Earth was still so hot that it was mostly molten, and debris flung from the impact is thought to have formed the moon.

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Materials deep inside Earth have unexpected atomic properties that might force earth scientists to revise their models of Earth's internal processes. Recreating in the lab materials they believe exist in the lowermost mantle 2,900 kilometres below Earth's surface, researchers say the materials exhibit unexpected atomic properties that might influence how heat is transferred within Earth's mantle, how superplumes form, and how the magnetic field and heat generated in Earth's core travel to the planet's surface.

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A new observation of the very deepest part of the Earth, the solid inner core, has been reported this week in Nature. The team from the University of Bristol also observed intriguing evidence of a texture in the solid iron that may reflect the patterns left as the swirling liquid iron of the outer core freezes to form the inner core.
Researchers at the University of Bristol have measured PKJKP an elusive seismic wave which traverses the Earths solid inner core with greater precision than ever before. This was achieved using Hi-net, an array of over 750 seismometers which span the Japanese islands and are designed to provide earthquake warnings.

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Title: Rapidly changing flows in the Earth's core
Authors: Nils Olsen & Mioara Mandea

A large part of the Earth's magnetic field is generated by fluid motion in the molten outer core. As a result of continuous satellite measurements since 1999, the core magnetic field and its recent variations can now be described with a high resolution in space and time. These data have recently been used to investigate small-scale core flow, but no advantage has yet been taken of the improved temporal resolution, partly because the filtering effect of the electrically conducting mantle was assumed to mask short-period magnetic variations. Here we show that changes in the magnetic field occurring over only a few months, indicative of fluid flow at the top of the core, can in fact be resolved. Using nine years of magnetic field data obtained by satellites as well as Earth-based observatories, we determine the temporal changes in the core magnetic field and flow in the core. We find that the core flow is spatially localised and involves rapid variations over a few months, with surprisingly large local accelerations. Our results suggest that short-term fluctuations of the core magnetic field are robust features of rapid core dynamics and should be considered in the development of future numerical models of the geodynamo.

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It is hard to know what is going on over 3000 km beneath our feet, but until recently scientists were fairly confident that they understood the way the iron atoms in the Earth's core packed together. However, new research has overturned conventional thinking and revealed that the structure of the core is not as straightforward as was once thought.
Pressures and temperatures at the Earth's core are stupendous - more than 3.5 Mbar and 7000*K - and currently it is impossible to recreate these conditions in the laboratory. Our information about the core comes from observing the way that seismic waves travel through the core, extrapolating from experimental studies and studying iron rich meteorites.
As a result we know that the core is mostly iron, but that it also must contain some light impurities such as oxygen, silicon, sulphur, hydrogen and magnesium (because the density of the core is too low to be pure iron). The most significant impurity is thought to be nickel, which makes up between 5 and 15% of the composition.
Most studies on the Earth's core have approximated the composition to be pure iron.

"It was assumed that the alloy elements were not very important for the structural and elastic properties of the core" - Igor Abrikosov, a theoretical physicist at Linköping University in Sweden.

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The Earth's core rotates faster than its surface by about 0.3 to 0. 5 degrees per year.

Earth`s iron core consists of a solid inner core about 2,400 km in diameter and a fluid outer core about 7,000 km in diameter. The inner core plays an important role in the geodynamics that generates Earth's magnetic field, and an electromagnetic torque from the geodynamics is thought to drive the inner core to rotate relative to the mantle and crust.
The first observational evidence for differential rotation was presented in 1996. For the past nine years, some seismologists have suspected that flaws, or artefacts, in the data were responsible for the purported movement.
But by comparing historical seismic waves traversing Earth's fluid and solid cores, the researchers found compelling evidence for differential rotation of the solid inner core.
They reported observations of 17 sets of similar seismic waves, which are called waveform doublets, from earthquakes occurring in the South Sandwich Islands region off the coast of South America.
The doublets, which were recorded at up to 58 seismic stations in and near Alaska with a time separation of up to 35 years, allowed the researchers to detect temporal changes along the sampling paths.
The similar seismic waves that passed through the inner core show systematic changes in travel times, and wave shapes when the two events of the doublet are separated in time by several years. The only plausible explanation is a motion of the inner core.
The most likely explanation for why the inner core is rotating at a different speed is electromagnetic coupling.
The magnetic field generated in the outer core diffuses into the inner core, where it generates an electric current. The interaction of that electric current with the magnetic field causes the inner core to spin, like the armature in an electric motor.
The fluid outer core decouples the solid inner core's movement from the mantle. Because the fluid outer core is not very viscous, frictional drag is small.

"Differential rotation is a fundamental dynamic process that goes to the heart of the origin of our planet and how it has evolved. There is still much to learn about the inner Earth" - Xiaodong Song, professor of geology at the University of Illinois at Urbana-Champaign and co-author of the paper.


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Scientists at Columbia University's Lamont-Doherty Earth Observatory and the University of Illinois at Urbana-Champaign have ended a nine-year debate over whether the Earth's inner core is undergoing changes that can be detected on a human timescale.
Their work, which appears in the August 26 issue of the journal Science, measured differences in the time it took seismic waves generated by nearly identical earthquakes up to 35 years apart to travel through the Earth's inner core.

"Our observations confirm the change of inner core travel times, which was first claimed by Song and Richards in 1996. This should settle the debate on whether these changes are real or an artefact of the original measurement method, and get us back to the work of understanding the history and dynamics of our planet" - Jian Zhang, a doctoral student in seismology at Lamont-Doherty and one of the study's co-lead authors.



Earth's core consists of a solid inner core about 2,400 km in diameter and a fluid outer core about 7,000 km across. The inner core plays an important role in the geodynamo that generates Earth's magnetic field.

In 1996, two of the current study's authors, Paul Richards of Lamont-Doherty and Xiaodong Song, then a post-doctoral researcher at Lamont-Doherty and now an associate professor at Illinois, presented evidence based on three decades of seismological records that they said showed the inner core was rotating approximately one degree per year faster than the rest of the planet.
Their study received substantial popular acclaim, but also drew criticism from some of their peers. In particular, a few scientists challenged their conclusions based on the fact that their results were right at the edge of what could be claimed.

To address the criticism, groups led by Richards and Song began looking for so-called waveform doublets--earthquakes that occur in essentially the same location and are detected at the same seismic recording station. If such earthquakes could be found, they reasoned, then measurements of changes in travel time could be made much more precisely.

The breakthrough came when Zhang found a September 2003 earthquake in the South Atlantic near the South Sandwich Islands that was detected in Alaska and provided a near-exact match with one that had occurred in December 1993. Zhang, Richards and their colleagues were able to see that the seismograms were almost identical for waves that had travelled only in the mantle and outer core.
The waves that had travelled through the inner core, however, looked slightly different--they had made the trip through the Earth 1/10 of a second faster in 2003 than in 1993.
Moreover, the shape of the waves themselves changed perceptibly after 10 years. In all, the scientists analyzed 18 doublets from 30 earthquakes in the South Sandwich Islands that were detected at 58 seismic stations in Alaska between 1961 and 2004.

In general, they found that waves passing through the inner core arrived noticeably earlier the more the earthquakes were separated in time. Interpreting this in terms of the known variability of wave speeds, they concluded that material which permits seismic waves to travel faster through the Earth had moved into the path taken by waves travelling through the inner core.
They calculated that this movement is caused by the core rotating approximately 0.3-0.5 degrees faster than the rest of the Earth. In addition, the change in the shape of the seismic waves is apparently caused, by inhomogeneity or "lumpiness" of the inner core, which has a varying influence on seismic waves produced years apart.

"For decades, people thought of the Earth's interior as changing very slowly over millions of years. This shows that we live on a remarkably dynamic planet. It also underscores the fact that we know more about the moon than about what's beneath our feet. Now we need to understand what is driving these changes" - Richards, Mellon Professor of the Natural Sciences at Columbia.

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