Unknown
In:
Phys. Earth Plan. Int., Warszawa, Elsevier, vol. 92, no. 12, pp. 39-44, pp.
L11309, (ISBN: 0-12-018847-3)
Publication Date:
1995
Description:
Mode conversions and reflections at upper-mantle seismic discontinuities may
be contained in earthquake seismograms as weak secondary phases that often become
visible only after special signal processing techniques are applied to the data. To
extract fully the information these secondary phases carry about the three-dimensional
structure of the Earth, new observational and interpretational methods have to be
developed. However, new sources of possible systematic errors may lead to conflicting
results. Studies carried out by various research groups on the thickness of the
upper-mantle transition zone, the sharpness of upper-mantle discontinuities and the
global existence of a 520 km discontinuity are examples where such discrepancies did
arise. Although there is a general consensus that the depths to the 410 km and 660 km
discontinuities vary by a few tens of kilometres at most, the question of wither the
depth variations of the 410 km and 660 km discontinuities are correlated or
anticorrelated is still unresolved. Similarly, different data sets and methods yielded
different answers on the sharpness of the upper-mantle discontinuities at 410 km and 660
km depth. Finally, data apparently supporting the global existence of a seismic
discontinuity at 520 km depth can be equally well explained by models that do not
contain this discontinuity.
Keywords:
Seismology
;
earth mantle
;
Gossler
;
PEPI
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