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Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle

Observations of shear wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D [Formula: see text] layer), based on differences in the arrival...

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Detalles Bibliográficos
Autores principales: Parisi, Laura, Ferreira, Ana M. G., Ritsema, Jeroen
Formato: Online Artículo Texto
Lenguaje:English
Publicado: John Wiley and Sons Inc. 2018
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6049884/
https://www.ncbi.nlm.nih.gov/pubmed/30034981
http://dx.doi.org/10.1002/2017JB014394
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author Parisi, Laura
Ferreira, Ana M. G.
Ritsema, Jeroen
author_facet Parisi, Laura
Ferreira, Ana M. G.
Ritsema, Jeroen
author_sort Parisi, Laura
collection PubMed
description Observations of shear wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D [Formula: see text] layer), based on differences in the arrival times of vertically (S V) and horizontally (S H) polarized shear waves. By computing waveforms at a period > 6 s for a wide range of 1‐D and 3‐D Earth structures, we illustrate that a time shift (i.e., apparent splitting) between S V and S H may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection s S. For deep earthquakes, apparent splitting can be due to the S wave triplication in D [Formula: see text] , reflections off discontinuities in the upper mantle, and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations.
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spelling pubmed-60498842018-07-20 Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle Parisi, Laura Ferreira, Ana M. G. Ritsema, Jeroen J Geophys Res Solid Earth Research Articles Observations of shear wave anisotropy are key for understanding the mineralogical structure and flow in the mantle. Several researchers have reported the presence of seismic anisotropy in the lowermost 150–250 km of the mantle (i.e., D [Formula: see text] layer), based on differences in the arrival times of vertically (S V) and horizontally (S H) polarized shear waves. By computing waveforms at a period > 6 s for a wide range of 1‐D and 3‐D Earth structures, we illustrate that a time shift (i.e., apparent splitting) between S V and S H may appear in purely isotropic simulations. This may be misinterpreted as shear wave anisotropy. For near‐surface earthquakes, apparent shear wave splitting can result from the interference of S with the surface reflection s S. For deep earthquakes, apparent splitting can be due to the S wave triplication in D [Formula: see text] , reflections off discontinuities in the upper mantle, and 3‐D heterogeneity. The wave effects due to anomalous isotropic structure may not be easily distinguished from purely anisotropic effects if the analysis does not involve full waveform simulations. John Wiley and Sons Inc. 2018-05-11 2018-05 /pmc/articles/PMC6049884/ /pubmed/30034981 http://dx.doi.org/10.1002/2017JB014394 Text en ©2018. The Authors. This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
spellingShingle Research Articles
Parisi, Laura
Ferreira, Ana M. G.
Ritsema, Jeroen
Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle
title Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle
title_full Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle
title_fullStr Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle
title_full_unstemmed Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle
title_short Apparent Splitting of S Waves Propagating Through an Isotropic Lowermost Mantle
title_sort apparent splitting of s waves propagating through an isotropic lowermost mantle
topic Research Articles
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6049884/
https://www.ncbi.nlm.nih.gov/pubmed/30034981
http://dx.doi.org/10.1002/2017JB014394
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