Anti-Correlated Seismic Velocity Anomalies from Post-Perovskite in the Lowermost Mantle

Anti-Correlated Seismic Velocity Anomalies from Post-Perovskite in the Lowermost Mantle (A) P-wave double array stacking results for two 5° latitudinal bins beneath the Cocos Plate. The solid black line shows the data stack amplitude relative to the direct P amplitude. The grey shaded region is the 95% confidence interval of the stack from bootstrap re-sampling, and the dashed line is the number of seismograms contributing to the data stack at a particular depth (right scales). Above 400 km the stack for 5-10°N is contaminated by P coda. The red lines are stacks of synthetic seismograms generated from our preferred models. The synthetics were sampled to match the source-receiver geometry and had the same processing as the data. (B) Elasticity models obtained by modeling the data: ρ is density (gm/cm3), V is S-wave velocity (km/s), Vb is bulk-sound velocity (km/s) and Vp is P-wave velocity (km/s). Percent changes in these parameters are shown at first-order discontinuities at the indicated depths. The depth range likely to contain post-perovskite (pPv) is indicated on the right.<p>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 resolves structures above the core-mantle boundary (CMB). 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 = [Vp2−4/3Vs2]**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 negligible effect on the bulk modulus while increasing the shear modulus by ~6%, resulting in local anti-correlation of Vb and Vs anomalies; this explains the data well.
</p><p>Hutko, A. R., T. Lay, J. Revenaugh, E. J. Garnero (2008). Anti-correlated seismic velocity anomalies from post-perovskite in the lowermost
mantle, Science, 320, 1070-1074.
</p><p>Acknowledgements: This work was supported in part by the U.S. National Science Foundation under grants EAR-0453884, and EAR-0453944.</p>


No comments yet.



Welcome to the IRIS Image Gallery – a diverse collection of photographs and visuals that encompass the range and breadth of seismology and the seismological community.

Please browse through our albums. These low and medium-resolution images can be freely used for personal and educational/academic purposes, but we request you recognize the image contributor by including in your product or presentation the credit displayed with each image.

More information is available in the Image Use Agreement.

If you have any comments, questions, or suggestions related to the IRIS Image Gallery, you can send them to

Photo info

Popular tags