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Constraints on small-scale heterogeneity in the lowermost mantle from observations of near podal PcP precursors

Zhang, Baolong and Ni, Sidao and Sun, Daoyuan and Shen, Zhichao and Jackson, Jennifer M. and Wu, Wenbo (2018) Constraints on small-scale heterogeneity in the lowermost mantle from observations of near podal PcP precursors. Earth and Planetary Science Letters, 489 . pp. 267-276. ISSN 0012-821X. http://resolver.caltech.edu/CaltechAUTHORS:20180327-075916427

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Abstract

Volumetric heterogeneities on large (∼>1000 km) and intermediate scales (∼>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 (∼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.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.epsl.2018.01.033DOIArticle
https://www.sciencedirect.com/science/article/pii/S0012821X18300517PublisherArticle
ORCID:
AuthorORCID
Sun, Daoyuan0000-0003-4461-4664
Additional Information:© 2018 Elsevier B.V. Received 29 August 2017, Revised 25 January 2018, Accepted 29 January 2018, Available online 14 March 2018. We thank the State Earthquake Information Service-Data Management Center of China, National Research Institute for Earth Science and Disaster Prevention of Japan, Incorporated Research Institutions for Seismology Data Management Center for providing data used in this study. Seismic Analysis Code (SAC) and Generic Mapping Tools package (GMT) are used for data processing and figure plotting. This work was supported by funding from the Strategic Priority Research Program (B) of Chinese Academy of Sciences (grant XDB18000000), National Basic Research Program of China (973 Program) through grant 2014CB845901 and National Natural Science Foundation of China 41574037. We are also thankful to NSF-CSEDI-EAR-1322082 and the W.M. Keck Institute for Space Studies for financial support.
Group:Seismological Laboratory, Keck Institute for Space Studies
Funders:
Funding AgencyGrant Number
Chinese Academy of SciencesXDB18000000
National Basic Research Program of China2014CB845901
National Natural Science Foundation of China41574037
NSFEAR-1322082
Keck Institute for Space Studies (KISS)UNSPECIFIED
Subject Keywords:near podal PcP precursor; lowermost mantle; small-scale heterogeneity
Record Number:CaltechAUTHORS:20180327-075916427
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20180327-075916427
Official Citation:Baolong Zhang, Sidao Ni, Daoyuan Sun, Zhichao Shen, Jennifer M. Jackson, Wenbo Wu, Constraints on small-scale heterogeneity in the lowermost mantle from observations of near podal PcP precursors, Earth and Planetary Science Letters, Volume 489, 2018, Pages 267-276, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2018.01.033. (http://www.sciencedirect.com/science/article/pii/S0012821X18300517)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85441
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:27 Mar 2018 18:35
Last Modified:27 Mar 2018 18:35

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