PROBLEMS OF GEOCOSMOS

Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)
strong scattering in D’’. This fairly minor contribution to PKiKP coda from shells above the ICB to a lesser
degree can be confirmed by absence of PcP codas from the decay curves estimated for other distances of the
dataset. Finally, as to relation between the parent phase and its coda, we note long spindle-shaped coda after
barely visible PKiKP in path #5, and almost identical PKiKP codas observed in paths #8 and #9 in spite of
weak and strong PKiKP waveforms detected at the head accordingly. Thus propagation of direct PKiKP
through D’’ and upper Earth’s shells turned out to be weak alternative to formation of PKiKP coda in the
inner core, while contribution from P scattered to PKP on the source or receiver side may be more
significant, especially at longer distances. However, this mechanism was recently shown [Leyton and Koper,
2007] to be invalid for PKiKP coda, at least for the case of single scattering and the adopted assumptions,
whereas heterogeneities in the outermost 350 km of the IC were favored to cause the PKiKP coda.
Fig. 2. Seismic coda decay curves estimated for paths
#2 (A), #3 (B), #4 (C) and #7 (D). Δ - epicentral
distance.
Fig. 3. ICB reflection/transmission coefficients. The
upper black and gray curves correspond to waves
PKIKP and PKJKP transmitted into the IC as P and S,
accordingly, and the bottom black is for PKiKP.
Fig. 4. Overlaid PKiKP coda doublets and beams plotted aligned on predicted
PKiKP arrival (zero time).
Unfortunately, the published envelope modeling [Leyton and Koper, 2007] is non-unique in terms of
scattering mechanisms and gives no clue as to whether we can discard reverberative PKiKP coda generation
theory and hypothesized discontinuities within the IC either local or global. In attempt to distinguish between
different physical scenarios of PKiKP coda generation, we first analyze fine structure of PKiKP coda
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