Journal article
Normal mode observability of radial anisotropy in the Earth’s mantle
- Abstract:
- Observations of seismic anisotropy provide useful information to infer directions of mantle flow. However, existing global anisotropic tomography models are not consistent, particularly in the lower mantle. Therefore, the interpretation of seismic anisotropy in terms of mantle dynamics and evolution remains difficult. While surface and body waves are commonly used to build radially anisotropic tomography models, they provide heterogeneous data coverage and the radial anisotropy structure retrieved using these data may be biased by the use of imperfect crustal corrections. Normal modes, the free oscillations of the Earth, automatically provide global data coverage and their sensitivity to shear-wave (vs) and compressional-wave (vp) velocity makes them suitable to study both vs and vp anisotropy in the mantle. In this study, we assess whether current normal mode splitting data have sufficient sensitivity to lower mantle anisotropy to potentially constrain it. We consider the uncertainties in the data and the effect of inaccuracies in crustal thickness corrections and the assumed scaling between vp and vs. We perform forward modelling of normal mode data using six different 3-D global radially anisotropic tomography models to document how strong and widespread anisotropy has to be to be observable in current normal mode data. We find that, on average 50 per cent of the spheroidal and 55 per cent of the toroidal modes investigated show significant sensitivity to vs anisotropy, while roughly 57 per cent of the spheroidal modes also have strong sensitivity to vp anisotropy. Moreover, we find that the normal mode data fit varies substantially for the various anisotropic tomography models considered, with the addition of anisotropy not always improving the data fit. While we find that crustal thickness corrections do not strongly impact modes that are sensitive to the lower mantle, we observe a trade-off between radial anisotropy and vp scaling for these modes. As long as this is taken into consideration, our findings suggest that existing normal mode data sets can provide valuable information on both vs and vp anisotropy in the mantle.
- Publication status:
- Published
- Peer review status:
- Peer reviewed
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- Files:
-
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(Preview, Accepted manuscript, pdf, 1.9MB, Terms of use)
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- Publisher copy:
- 10.1093/gji/ggac474
Authors
- Publisher:
- Oxford University Press
- Journal:
- Geophysical Journal International More from this journal
- Volume:
- 233
- Issue:
- 1
- Pages:
- 663–679
- Publication date:
- 2022-12-01
- Acceptance date:
- 2022-11-25
- DOI:
- EISSN:
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1365-246X
- ISSN:
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0956-540X
- Language:
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English
- Keywords:
- Pubs id:
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1311037
- Local pid:
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pubs:1311037
- Deposit date:
-
2022-12-02
Terms of use
- Copyright holder:
- Restelli et al.
- Copyright date:
- 2022
- Rights statement:
- © The Author(s) 2022. Published by Oxford University Press on behalf of The Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
- Notes:
- This is a pre-copyedited, author-produced PDF of an article accepted for publication in Geophysical Journal International following peer review. The version of record is available at: 10.1093/gji/ggac474
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