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

In English

Författare

Summary, in English

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.

Publiceringsår

2004

Språk

Engelska

Sidor

469-481

Publikation/Tidskrift/Serie

Physics of the Earth and Planetary Interiors

Volym

146

Issue

3-4

Dokumenttyp

Artikel i tidskrift

Förlag

Elsevier

Ämne

  • Mechanical Engineering

Status

Published

ISBN/ISSN/Övrigt

  • ISSN: 0031-9201