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| Titel |
Seismic structure of the Earth's core |
| VerfasserIn |
Arwen Deuss, Jessica Irving, Lauren Waszek, Anna Makinen |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250037671
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| Zusammenfassung |
| The Earth’s core, consisting of an iron alloy, makes up one third of our planet’s total mass.
As the Earth cools, the inner core grows by solidification of the fluid outer core.
Solidification results in the release of light elements and latent heat, which drive the
geodynamo generating the Earth’s magnetic field. It is well known from seismological
observations that the inner core is anisotropic and possibly rotating faster than the Earth’s
mantle. Here, we study the seismic structure of the inner core using both short
period compressional body wave observations and long period normal mode splitting
functions.
Using compressional body waves, we find evidence for hemispherical variations in the
isotropic and anisotropic structure of the Earth’s inner core, confirming previous
studies. However, because of the limited distribution of earthquakes and receivers, the
global extent of the hemispherical variations is poorly constrained. The observed
signal may, for example, be due to more complicated regional variations. Normal
mode observations have the potential to provide robust evidence, but so far been
elusive due to lack of theory and suitable data. Previous studies have investigated
isolated modes, which are only sensitive to even-degree structure, and showed strong
evidence for inner core anisotropy. To investigate hemispherical variations, which is
odd-degree structure, cross-coupling between pairs of modes has to be taken into
account.
Here, we report splitting function observations of odd-degree structure for pairs of
coupled modes sensitive to the inner core in comparison with body wave observations. The
observed odd-degree structure suggests more complicated regional variations than a simple
Eastern versus Western hemispherical pattern and opens up possibilities for directly linking
regional variations in inner core structure to the strength of the magnetic field and thermal
evolution of the Earth’s core. Such links would be limited by the possible super rotation of
the inner core, which we show may be less robustly found in seismic data than has been
claimed in previous studies. |
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