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| Titel |
Effect of upper mantle inhomogeneities on the amplitudes of body waves: consequences for the interpretation of deep earth structure |
| VerfasserIn |
H. Tkalcic, V. F. Cormier, B. L. N. Kennett |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027506
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| Zusammenfassung |
| Recent expansion of broadband seismic data have yielded a large number of new observations
of PcP and PKiKP waves that reflect from the Earth’s outer and inner core. Simultaneous
observations of these waves are particularly important as they allow direct estimates of the
density contrast at the inner core boundary, the quantity that has been a subject
of debate in seismological community for forty years. This quantity is important
for the understanding of the thermal evolution of the Earth’s inner core and the
geodynamo.
We have recently shown that the amplitude ratios of these new data argue for a complex
rather than simple inner core boundary. The variation of PKiKP/PcP amplitude ratios might
be interpreted as a direct evidence for unequally solidified regions at the top of the inner core.
While most estimates from these body waves are very close to the predictions from the
spherically symmetric models of the Earth and normal modes (600 kg/m3), some yield as low
density contrast as 200-300 kg/m3.
We have found, however, a striking anti-correlation in the observations of PcP and PKiKP
waves. We show that this anti-correlation is unlikely related to the variations in the source
radiation pattern. We also demonstrate that the lowermost mantle or the core mantle boundary
is an unlikely source of the observed anti-correlation. We favour a mechanism in which
inhomogeneities in the upper mantle on the receiver side effect amplitudes of PcP and PKiKP
waves, and are the cause of the observed anti-correlation. A number of numerical
experiments were conducted to model the amplitude ratios, including a search for the
mechanism for reproducing an observed anti-correlation of the amplitude of these wave
types. Only in those cases when the effect of inhomogeneities is similar on both
amplitudes, these data will allow credible measurements of the density contrast at the
inner core boundary. If these effects are disregarded, this may result in erroneous
estimates of the density contrast at the inner core boundary and other deep earth
parameters. |
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