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| Titel |
Probing the inner core’s African hemisphere boundary with P′P′ |
| VerfasserIn |
Elizabeth Day, James Ward, Ian Bastow, Jessica Irving |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250148878
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| Publikation (Nr.) |
 EGU/EGU2017-13175.pdf |
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| Zusammenfassung |
| Geophysical observations of the inner core today improve our understanding not just of the
processes occurring in the core at the present, but also those that occurred in the past. As the
inner core freezes it may record clues as to the state of the Earth at the time of growth; the
texture in the inner core may also be modified through post-solidification deformation. The
seismic structure of the inner core is not simple; the dominant pattern is one of anisotropic
and isotropic differences between the Eastern and Western ’hemispheres’ of the inner
core. Additionally, there is evidence for an innermost inner core, layering of the
uppermost inner core, and possibly super-rotation of the inner core relative to the
mantle.
Most body wave studies of inner core structure use PKP-PKIKP differential travel times to
constrain velocity variations within the inner core. However, body wave studies are
inherently limited by the geometry of seismic sources and stations, and thus there
are some areas of the inner core that are relatively under-sampled, even in today’s
data-rich world. Here, we examine the differential travel times of the different branches
of P′P′ (PKIKPPKIKP, or P′P′df, and PKPPKP), comparing the arrival time of
inner core turning branch P′P′df with the arrival times of branches that turn in the
outer core. By using P′P′ we are able to exploit different ray geometries and sample
different regions of the inner core to those areas accessible to studies which utilize
PKIKP.
We use both linear and non-linear stacking methods to make observations of the small
amplitude P′P′ phases. We identify the three P′P′ branches, as well as pre- and post-cursors to
the main arrivals, which can cause confusion. To facilitate identifying each P′P′ branch we
make AxiSEM synthetics, carry out beamforming, and use bootstrapping to access the
robustness of our observations, which focus on the inner core’s hemisphere boundary beneath
Africa.
Our measurements match the broad scale hemispherical pattern of anisotropy in the inner
core, but also show some small scale variations. |
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