Seismic anisotropy in the D″ layer

Vinnik, Lev; Romanowicz, Barbara; Stunff, Yves Le; Makeyeva, Larissa

doi:10.1029/95gl01327

Cited by 96 publications

(54 citation statements)

References 11 publications

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“…The presence of anisotropy in the D" region has been recognized by several previous studies (Vinnik et al, 1989(Vinnik et al, , 1995(Vinnik et al, , 1998Maupin, 1994;Kendall and Silver, 1996;Matzel et al, 1996;Garnero and Lay, 1997;Lay et al, 1998b). The presence of anisotropy is a remarkable feature particularly because the absence of anisotropy in most of the lower mantle is well documented (Kaneshima and Silver, 1992;Meade et al, 1995;Montagner and Kennett, 1996).…”

Section: Introductionmentioning

confidence: 73%

Some remarks on the origin of seismic anisotropy in the D” layer

Karato

2014

Earth Planet Sp

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Physical mechanisms of seismic anisotropy in the D" layer are examined based on seismological and mineral physics observations. The results of body-wave seismology on the fine structure of the D" layer and of mineral physics studies on the elastic constants and the lattice preferred orientation in lower mantle minerals as well as the shape preferred orientation of melt pockets are taken into account. Evidence of large but depth (pressure)-dependent elastic anisotropy of lower mantle minerals, particularly (Mg,Fe)O, and of tilted shape preferred orientation of sheared partial melts is summarized. It is shown that both shape preferred orientation of partial melts (or iron-rich secondary phases) and lattice preferred orientation of minerals with well-documented slip systems are difficult to reconcile with seismological observations. However, lattice preferred orientation of highly anisotropic mineral, (Mg,Fe)O, is consistent with most of the seismic observations if the dominant glide plane under the D" layer conditions is {100} rather than {110} as observed at lower pressures. Such a change in glide plane in MgO (or (Mg,Fe)O) is likely to occur as a result of pressure-induced change in elastic anisotropy and/or in the nature of chemical bonding (and possibly due to high temperatures). Both solid-state and partial melt mechanisms of anisotropy imply that the V SH > V SV (V SV > V SH ) polarization anisotropy means horizontal (vertical) flow. In the solid-state mechanism, significant V SH > V SV in the D" layer beneath the circum-Pacific (Alaska and the Caribbean) implies horizontal shear at high stress caused presumably by the collision of subducting materials with the core-mantle boundary. Highly variable anisotropy beneath the central-Pacific can be attributed to solid-state fabrics caused by a complicated threedimensional flow presumably related to the upwelling of plumes, but anisotropy in this region could also be attributed to the shape preferred orientation of melt pockets the presence of which is suggested by very low average velocities.

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Section: Introductionmentioning

confidence: 73%

Some remarks on the origin of seismic anisotropy in the D” layer

Karato

2014

Earth Planet Sp

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“…Our understanding of the structural complexity of D" has been expanded by recent observations of shear wave splitting (usually involving delay of onset of the SV component of motion as compared to the SH component) for core-grazing and diffracted waves [Vinnik et al, 1989[Vinnik et al, , 1995Lay and Young, 1991;Maupin, 1994;Matzel et al, 1996;Kendall and Silver, 1996]. Earlier work documented similar splitting for core-reflected ScS waves [Mitchell and Helmberger, 1973;Lay and Helmberger, 1983b].…”

mentioning

confidence: 87%

Lateral variations in lowermost mantle shear wave anisotropy beneath the north Pacific and Alaska

1997

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“…The lowermost layer of the lower mantle exhibits unusually high seismic anisotropy (Lay and Young, 1991;Vinnik et al, 1995;Kendall and Silver, 1996;Montagner and Kennett, 1996). Among the explanations for this observation is the development of a lattice preferred orientation in (Mg,Fe)SiO 3 post-perovskite.…”

Section: Polycrystal Anisotropymentioning

confidence: 99%

MSAT—A new toolkit for the analysis of elastic and seismic anisotropy

Walker

Wookey

2012

Computers & Geosciences

156

124

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The design and content of MSAT, a new Matlab toolkit for the study and analysis of seismic and elastic anisotropy, is described. Along with a brief introduction to the basic theory of anisotropic elasticity and a guide to the functions provided by the toolkit, three example applications are discussed. First, the toolkit is used to analyse the effect of pressure on the elasticity of the monoclinic upper mantle mineral diopside. Second, the degree to which a model of elasticity in the lowermost mantle can be approximated by transverse isotropy is examined. Finally backazimuthal variation in the effective shear wave splitting caused by two anisotropic layers where the lower layer is dipping is calculated. MSAT can be freely reused for any purpose and the implementation of these and other examples are distributed with the source code.

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Seismic anisotropy in the D″ layer

Cited by 96 publications

References 11 publications

Some remarks on the origin of seismic anisotropy in the D” layer

Some remarks on the origin of seismic anisotropy in the D” layer

Lateral variations in lowermost mantle shear wave anisotropy beneath the north Pacific and Alaska

MSAT—A new toolkit for the analysis of elastic and seismic anisotropy

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