期刊
EARTH AND PLANETARY SCIENCE LETTERS
卷 489, 期 -, 页码 267-276出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.epsl.2018.01.033
关键词
near podal PcP precursor; lowermost mantle; small-scale heterogeneity
资金
- Strategic Priority Research Program (B) of Chinese Academy of Sciences [XDB18000000]
- National Basic Research Program of China (973 Program) [2014CB845901]
- National Natural Science Foundation of China [41574037]
- W.M. Keck Institute for Space Studies
- [NSF-CSEDI-FAR-1322082]
Volumetric heterogeneities on large (>1000 km) and intermediate scales (similar to->100 km) in the lowermost mantle have been established with seismological approaches. However, there are controversies regarding the level of heterogeneity in the lowermost mantle at small scales (a few kilometers to tens of kilometers), with lower bound estimates ranging from 0.1% to a few percent. We take advantage of the small amplitude PcP waves at near podal distances (0-12) to constrain the level of small-scale heterogeneity within 250 km above the CMB. First, we compute short period synthetic seismograms with a finite difference code for a series of volumetric heterogeneity models in the lowermost mantle, and find that PcP is not identifiable if the small-scale heterogeneity in the lowermost mantle is above 2.5%. We then use a functional form appropriate for coda decay to suppress P coda contamination. By comparing the corrected envelope of PcP and its precursors with synthetic seismograms, we find that perturbations of small-scale (similar to 8 km) heterogeneity in the lowermost mantle is 0.2-0.5% beneath regions of the China-Myanmar border area, Okhotsk Sea and South America. Whereas strong perturbations (-1.0%) are found beneath Central America. In the regions studied, we find that this particular type of small-scale heterogeneity in the lowermost mantle is weak, yet there are some regions requiring heterogeneity up to 1.0%. Where scattering is stronger, such as under Central America, more chemically complex mineral assemblages may be present at the core-mantle boundary. (C) 2018 Elsevier B.V. All rights reserved.
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