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Rolling hills on the core–mantle boundary

Sun, Daoyuan and Helmberger, Don V. and Jackson, Jennifer M. and Clayton, Robert W. and Bower, Dan J. (2013) Rolling hills on the core–mantle boundary. Earth and Planetary Science Letters, 361 . pp. 333-342. ISSN 0012-821X. doi:10.1016/j.epsl.2012.10.027.

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Recent results suggest that an iron-rich oxide may have fractionally crystallized from a primordial magma ocean and settled on the core–mantle boundary (CMB). Based on experimental results, the presence of only a few percent of Fe-rich oxide could slow seismic waves down by several percent. This heavy layer can become highly undulating as predicted from dynamic modeling but can remain as a distinct structure with uniform velocity reductions. Here, we use the large USArray seismic network to search for such structures. Strong constraints on D″ are provided by the core-phase SKS where it bifurcates, containing a short segment of P-wave diffractions (P_d) when crossing the CMB, called SKS_d. Synthetics from models with moderate velocity drops (less than 10%) involving a layer with variable thickness, perhaps a composite of sharp small structures, with strong variation in thickness can explain both the observed SKS_d waveforms and large scatter in differential times between SKKS and SKS. A smooth 3D image is obtained from inverting SKS_d waveforms displaying rolling-hills with elongated dome-like structures sitting on the CMB. The most prominent one has an 80-km height, ∼8° length, and ∼4° width, thus adding still more structural complexity to the lower mantle. We suggest that these results can be explained by a dynamically-stabilized material containing small amounts (∼5%) iron-rich (Mg,Fe)O providing a self-consistent physical interpretation.

Item Type:Article
Related URLs:
URLURL TypeDescription DOIArticle
Sun, Daoyuan0000-0003-4461-4664
Jackson, Jennifer M.0000-0002-8256-6336
Clayton, Robert W.0000-0003-3323-3508
Bower, Dan J.0000-0002-0673-4860
Additional Information:© 2012 Elsevier B.V. Received 14 June 2012. Received in revised form 6 October 2012. Accepted 30 October 2012. Editor: P.Shearer Available online 11 December 2012. The authors would like to thank the Editor Peter Shearer and two anonymous reviewers for their constructive comments. We thank J. K. Wicks and M. Gurnis for stimulating conversations and a constructive review by Alex Song. Data were provided by IRIS data center sand Earth scope US Array. This work was supported by NSF CSEDI EAR-0855815. D. Sunis supported by a Carnegie fellowship at the Department of Terrestrial Magnetism, Carnegie Institution of Washington.
Group:Seismological Laboratory, Division of Geological and Planetary Sciences
Funding AgencyGrant Number
Carnegie Institution of Washington Department of Terrestrial MagnetismUNSPECIFIED
Subject Keywords:core–mantle boundary (CMB); iron-rich (Mg,Fe)O; USArray; low velocity zone
Record Number:CaltechAUTHORS:20130318-110208034
Persistent URL:
Official Citation:Daoyuan Sun, Don V. Helmberger, Jennifer M. Jackson, Robert W. Clayton, Dan J. Bower, Rolling hills on the core–mantle boundary, Earth and Planetary Science Letters, Volume 361, 1 January 2013, Pages 333-342, ISSN 0012-821X, 10.1016/j.epsl.2012.10.027. (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:37538
Deposited By: Ruth Sustaita
Deposited On:19 Mar 2013 15:16
Last Modified:09 Nov 2021 23:29

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