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| Titel |
SHdiff/SVdiff splitting in an isotropic Earth and anisotropy in D" |
| VerfasserIn |
Dimitri Komatitsch, Lev Vinnik, Sébastien Chevrot |
| 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 |
250038991
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| Zusammenfassung |
| The vertically-polarized SVdiff seismic phase sometimes arrives later than
the horizontally-polarized SHdiff. Both phases propagate in the D'' layer at
the base of the mantle and the difference in their arrival times is usually
interpreted in terms of seismic anisotropy in D''. Here, using numerical
simulations based on the spectral-element technique, we demonstrate that a
significant delay of SVdiff relative to SHdiff is
present even in the IASP91 isotropic reference Earth model and in a model
with a high S velocity in D'' relative to IASP91. The delay is accompanied by strong amplitude
decay of SVdiff with distance. This relationship resembles the
effect of anelasticity. In a model with a low S velocity in D'', the waveform
of SVdiff can be very different from SHdiff, and this
difference can be mistaken for a delay of SHdiff relative to SVdiff. In a
laterally-heterogeneous isotropic D'' SVdiff can also be delayed because,
unlike SHdiff, SVdiff has strong amplitude decay along fast paths. Its traveltime
is thus dominated by slow propagation paths and tends to be positively
biased. For D'' models with an S velocity difference of 3% between two
hemispheres, there are regions where SHdiff arrives up to 15 s earlier than
the first clearly visible SVdiff.
This is observed in a corridor several hundred kilometers wide.
If the effects that are observed in our experiments are misinterpreted
in terms of D'' anisotropy in actual seismic data,
estimates of anisotropy are biased and may contribute to the idea of seismic
anisotropy
being different in high- and low-S-velocity regions of D''. |
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