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Elastic anisotropy of experimental analogues of perovskite and post-perovskite help to interpret D'' diversity.

Yoneda A, Fukui H, Xu F, Nakatsuka A, Yoshiasa A, Seto Y, Ono K, Tsutsui S, Uchiyama H, Baron AQ - Nat Commun (2014)

Bottom Line: Recent studies show that the D'' layer, just above the Earth's core-mantle boundary, is composed of MgSiO3 post-perovskite and has significant lateral inhomogeneity.Our results show that Cmcm-CaIrO3 is much more elastically anisotropic than Pbnm-CaIrO3, which offers an explanation for the enigmatic seismic wave velocity jump at the D'' discontinuity.Considering the relation between lattice preferred orientation and seismic anisotropy in the D'' layer, we suggest that the c axis of post-perovskite MgSiO3 aligns vertically beneath the Circum-Pacific rim, and the b axis vertically beneath the Central Pacific.

View Article: PubMed Central - PubMed

Affiliation: Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682-0193, Japan.

ABSTRACT
Recent studies show that the D'' layer, just above the Earth's core-mantle boundary, is composed of MgSiO3 post-perovskite and has significant lateral inhomogeneity. Here we consider the D'' diversity as related to the single-crystal elasticity of the post-perovskite phase. We measure the single-crystal elasticity of the perovskite Pbnm-CaIrO3 and post-perovskite Cmcm-CaIrO3 using inelastic X-ray scattering. These materials are structural analogues to same phases of MgSiO3. Our results show that Cmcm-CaIrO3 is much more elastically anisotropic than Pbnm-CaIrO3, which offers an explanation for the enigmatic seismic wave velocity jump at the D'' discontinuity. Considering the relation between lattice preferred orientation and seismic anisotropy in the D'' layer, we suggest that the c axis of post-perovskite MgSiO3 aligns vertically beneath the Circum-Pacific rim, and the b axis vertically beneath the Central Pacific.

Show MeSH
Velocity surfaces of pPv-MgSiO3 at 125 GPa and 2,500 K.Blue lines are used to specify theoretical results similar to Fig. 2a,b. The upper line is the P-wave velocity and the lower lines are the S-wave velocities. Open circles ‘o’ and crosses ‘+’ for VS specify in-plane and out-of-plane particle motions.
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f7: Velocity surfaces of pPv-MgSiO3 at 125 GPa and 2,500 K.Blue lines are used to specify theoretical results similar to Fig. 2a,b. The upper line is the P-wave velocity and the lower lines are the S-wave velocities. Open circles ‘o’ and crosses ‘+’ for VS specify in-plane and out-of-plane particle motions.

Mentions: According to seismological studies, the region of the Circum-Pacific rim is interpreted as having VTI with VSH>VSV, while the region of the Central Pacific has complicated VTI without any fixed relation between VSH and VSV4. Polarization anisotropy is not recognized beneath the Atlantic Ocean, or the region is considered as having VTI with VSH≈VSV. On the other hand, from the polarization pattern in the a–b plane of the faster VS plot (Figs 2b and 7), we can expect that VSH>VSV in the D′′ layer if the c axis of pPv aligns vertically. Similarly, if the b axis aligns vertically, the magnitude relation between VSH and VSV can be complicated.


Elastic anisotropy of experimental analogues of perovskite and post-perovskite help to interpret D'' diversity.

Yoneda A, Fukui H, Xu F, Nakatsuka A, Yoshiasa A, Seto Y, Ono K, Tsutsui S, Uchiyama H, Baron AQ - Nat Commun (2014)

Velocity surfaces of pPv-MgSiO3 at 125 GPa and 2,500 K.Blue lines are used to specify theoretical results similar to Fig. 2a,b. The upper line is the P-wave velocity and the lower lines are the S-wave velocities. Open circles ‘o’ and crosses ‘+’ for VS specify in-plane and out-of-plane particle motions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3974219&req=5

f7: Velocity surfaces of pPv-MgSiO3 at 125 GPa and 2,500 K.Blue lines are used to specify theoretical results similar to Fig. 2a,b. The upper line is the P-wave velocity and the lower lines are the S-wave velocities. Open circles ‘o’ and crosses ‘+’ for VS specify in-plane and out-of-plane particle motions.
Mentions: According to seismological studies, the region of the Circum-Pacific rim is interpreted as having VTI with VSH>VSV, while the region of the Central Pacific has complicated VTI without any fixed relation between VSH and VSV4. Polarization anisotropy is not recognized beneath the Atlantic Ocean, or the region is considered as having VTI with VSH≈VSV. On the other hand, from the polarization pattern in the a–b plane of the faster VS plot (Figs 2b and 7), we can expect that VSH>VSV in the D′′ layer if the c axis of pPv aligns vertically. Similarly, if the b axis aligns vertically, the magnitude relation between VSH and VSV can be complicated.

Bottom Line: Recent studies show that the D'' layer, just above the Earth's core-mantle boundary, is composed of MgSiO3 post-perovskite and has significant lateral inhomogeneity.Our results show that Cmcm-CaIrO3 is much more elastically anisotropic than Pbnm-CaIrO3, which offers an explanation for the enigmatic seismic wave velocity jump at the D'' discontinuity.Considering the relation between lattice preferred orientation and seismic anisotropy in the D'' layer, we suggest that the c axis of post-perovskite MgSiO3 aligns vertically beneath the Circum-Pacific rim, and the b axis vertically beneath the Central Pacific.

View Article: PubMed Central - PubMed

Affiliation: Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682-0193, Japan.

ABSTRACT
Recent studies show that the D'' layer, just above the Earth's core-mantle boundary, is composed of MgSiO3 post-perovskite and has significant lateral inhomogeneity. Here we consider the D'' diversity as related to the single-crystal elasticity of the post-perovskite phase. We measure the single-crystal elasticity of the perovskite Pbnm-CaIrO3 and post-perovskite Cmcm-CaIrO3 using inelastic X-ray scattering. These materials are structural analogues to same phases of MgSiO3. Our results show that Cmcm-CaIrO3 is much more elastically anisotropic than Pbnm-CaIrO3, which offers an explanation for the enigmatic seismic wave velocity jump at the D'' discontinuity. Considering the relation between lattice preferred orientation and seismic anisotropy in the D'' layer, we suggest that the c axis of post-perovskite MgSiO3 aligns vertically beneath the Circum-Pacific rim, and the b axis vertically beneath the Central Pacific.

Show MeSH