Anticorrelated seismic velocity anomalies from post-perovskite in the lowermost mantle

Alexander R. Hutko, Thorne Lay, Justin Revenaugh, Edward Garnero

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Abstract

Earth's lowermost mantle has thermal, chemical, and mineralogical complexities that require precise seismological characterization. Stacking, migration, and modeling of over 10,000 P and S waves that traverse the deep mantle under the Cocos plate resolve structures above the core-mantle boundary. A small -0.07 ± 0.15% decrease of P wave velocity (Vp) is accompanied by a 1.5 ± 0.5% increase in S wave velocity (Vs) near a depth of 2570 km. Bulk-sound velocity [Vb = (V p 2 - 4/3Vs 2)1/2] decreases by -1.0 ± 0.5% at this depth. Transition of the primary lower-mantle mineral, (Mg1-x-y FexAly)(Si,Al) O3 perovskite, to denser post-perovskite is expected to have a negligible effect on the bulk modulus while increasing the shear modulus by ∼6%, resulting in local anticorrelation of Vb and Vs anomalies; this behavior explains the data well.

Original languageEnglish (US)
Pages (from-to)1070-1074
Number of pages5
JournalScience
Volume320
Issue number5879
DOIs
Publication statusPublished - May 23 2008

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