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Some comments on the effects of lower-mantle anisotropy on SKS and SKKS phases

Hall, Stephen LU ; Kendall, J. M. and van der Baan, M. (2004) In Physics of the Earth and Planetary Interiors 146(3-4). p.469-481
Abstract
Anisotropy in the lowermost few 100 km of mantle, or D" region, is indicative of deformation-induced alignment of crystals and/or inclusions of material, and as such offers insights into the dynamic nature of this region. Observations of shear-wave splitting in phases that transit this region provide constraints on such anisotropy. We investigate the effects of lower-mantle seismic anisotropy on SKS and SKKS phases through linked effective-medium modelling and ray-based waveform modelling. A mantle with vertical-transverse-isotropy (VTI) will not produce any splitting in such core phases. Instead we consider the effects of azimuthal-anisotropy due to aligned disk-shaped and tubular inclusions and aligned perovskite, peridase and columbite.... (More)
Anisotropy in the lowermost few 100 km of mantle, or D" region, is indicative of deformation-induced alignment of crystals and/or inclusions of material, and as such offers insights into the dynamic nature of this region. Observations of shear-wave splitting in phases that transit this region provide constraints on such anisotropy. We investigate the effects of lower-mantle seismic anisotropy on SKS and SKKS phases through linked effective-medium modelling and ray-based waveform modelling. A mantle with vertical-transverse-isotropy (VTI) will not produce any splitting in such core phases. Instead we consider the effects of azimuthal-anisotropy due to aligned disk-shaped and tubular inclusions and aligned perovskite, peridase and columbite. Models are constructed subject to constraints imposed by observed anisotropy (<3%) and plausible variations in aggregate isotropic velocities (< +/- 2.5%). Melt-filled inclusions are much more effective in generating anisotropy than solid-filled inclusions and disk-shaped inclusions produce more anisotropy than tubular inclusions. In general the degree of splitting produced by most of the models is small, similar to that produced by the crust (<0.5 s). The exceptions are melt-filled vertically-aligned disk-shaped inclusions and horizontally aligned periclase, the former most likely in low-velocity regions, the latter in high-velocity regions. Both models produce splitting significant enough to mask the effects of upper-mantle anisotropy. Strong azimuthal variations in splitting and discrepancies in SKS and SKKS splitting are diagnostic of these anisotropic models. (C) 2004 Published by Elsevier B.V. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
in
Physics of the Earth and Planetary Interiors
volume
146
issue
3-4
pages
469 - 481
publisher
Elsevier
external identifiers
  • Scopus:3543062826
ISSN
0031-9201
DOI
10.1016/j.pepi.2004.05.002
language
English
LU publication?
no
id
88a5e0ab-4772-40c7-a384-c2ef278480ed (old id 2441087)
date added to LUP
2012-04-27 14:27:40
date last changed
2016-10-13 04:57:57
@misc{88a5e0ab-4772-40c7-a384-c2ef278480ed,
  abstract     = {Anisotropy in the lowermost few 100 km of mantle, or D" region, is indicative of deformation-induced alignment of crystals and/or inclusions of material, and as such offers insights into the dynamic nature of this region. Observations of shear-wave splitting in phases that transit this region provide constraints on such anisotropy. We investigate the effects of lower-mantle seismic anisotropy on SKS and SKKS phases through linked effective-medium modelling and ray-based waveform modelling. A mantle with vertical-transverse-isotropy (VTI) will not produce any splitting in such core phases. Instead we consider the effects of azimuthal-anisotropy due to aligned disk-shaped and tubular inclusions and aligned perovskite, peridase and columbite. Models are constructed subject to constraints imposed by observed anisotropy (&lt;3%) and plausible variations in aggregate isotropic velocities (&lt; +/- 2.5%). Melt-filled inclusions are much more effective in generating anisotropy than solid-filled inclusions and disk-shaped inclusions produce more anisotropy than tubular inclusions. In general the degree of splitting produced by most of the models is small, similar to that produced by the crust (&lt;0.5 s). The exceptions are melt-filled vertically-aligned disk-shaped inclusions and horizontally aligned periclase, the former most likely in low-velocity regions, the latter in high-velocity regions. Both models produce splitting significant enough to mask the effects of upper-mantle anisotropy. Strong azimuthal variations in splitting and discrepancies in SKS and SKKS splitting are diagnostic of these anisotropic models. (C) 2004 Published by Elsevier B.V.},
  author       = {Hall, Stephen and Kendall, J. M. and van der Baan, M.},
  issn         = {0031-9201},
  language     = {eng},
  number       = {3-4},
  pages        = {469--481},
  publisher    = {ARRAY(0x8dfae88)},
  series       = {Physics of the Earth and Planetary Interiors},
  title        = {Some comments on the effects of lower-mantle anisotropy on SKS and SKKS phases},
  url          = {http://dx.doi.org/10.1016/j.pepi.2004.05.002},
  volume       = {146},
  year         = {2004},
}