3D transdimensional seismic tomography of the inner core
Body wave observations of the Earth's inner core show that it contains strong seismic heterogeneity, both laterally and radially. Models of inner core structure generated using body wave data are often limited by their parameterisation. Thus, it is difficult to determine whether features such a...
| Main Authors: | , , , , |
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| Other Authors: | |
| Format: | Journal Article |
| Language: | English |
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2022
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| Online Access: | https://hdl.handle.net/10356/163899 |
| _version_ | 1811693357825523712 |
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| author | Brett, Henry Hawkins, Rhy Waszek, Lauren Lythgoe, Karen Deuss, Arwen |
| author2 | Earth Observatory of Singapore |
| author_facet | Earth Observatory of Singapore Brett, Henry Hawkins, Rhy Waszek, Lauren Lythgoe, Karen Deuss, Arwen |
| author_sort | Brett, Henry |
| collection | NTU |
| description | Body wave observations of the Earth's inner core show that it contains strong seismic heterogeneity, both laterally and radially. Models of inner core structure generated using body wave data are often limited by their parameterisation. Thus, it is difficult to determine whether features such as anisotropic hemispheres or an innermost inner core truly exist with their simple shapes, or result only from the chosen parameterisation and are in fact more complex features. To overcome this limitation, we conduct seismic tomography using transdimensional Markov Chain Monte Carlo on a high quality dataset of 5296 differential and 2344 absolute P-wave travel times. In a transdimensional approach, the data defines the model space parameterisation, providing us with both the mean value of each model parameter and its probability distribution, allowing us to identify well versus poorly constrained regions. We robustly recover many first order observations found in previous studies without the imposition of a priori fixed geometry including an isotropic top layer (with anisotropy less than 1%) which is between 60 and 170 km thick, and separated into hemispheres with a slow west and a faster east. Strong anisotropy (with a maximum of 7.2%) is found mainly in the west, with much weaker anisotropy in the east. We observe for the first time that the western anisotropic zone is largely confined to the northern hemisphere, a property which would not be recognised in models assuming a simple hemispherical parameterisation. We further find that the inner most inner core, in which the slowest anisotropic velocity direction is tilted relative to Earth's axis of rotation (ζ=55∘±16∘), is offset by 400 km from the centre of the inner core and is restricted to the eastern hemisphere. We propose that this anomalous anisotropy might indicate the presence of a different phase of iron (either bcc or fcc) compared to the rest of the inner core (hcp). |
| first_indexed | 2024-10-01T06:50:24Z |
| format | Journal Article |
| id | ntu-10356/163899 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2024-10-01T06:50:24Z |
| publishDate | 2022 |
| record_format | dspace |
| spelling | ntu-10356/1638992022-12-24T23:31:06Z 3D transdimensional seismic tomography of the inner core Brett, Henry Hawkins, Rhy Waszek, Lauren Lythgoe, Karen Deuss, Arwen Earth Observatory of Singapore Science::Geology Inner Core Seismology Body wave observations of the Earth's inner core show that it contains strong seismic heterogeneity, both laterally and radially. Models of inner core structure generated using body wave data are often limited by their parameterisation. Thus, it is difficult to determine whether features such as anisotropic hemispheres or an innermost inner core truly exist with their simple shapes, or result only from the chosen parameterisation and are in fact more complex features. To overcome this limitation, we conduct seismic tomography using transdimensional Markov Chain Monte Carlo on a high quality dataset of 5296 differential and 2344 absolute P-wave travel times. In a transdimensional approach, the data defines the model space parameterisation, providing us with both the mean value of each model parameter and its probability distribution, allowing us to identify well versus poorly constrained regions. We robustly recover many first order observations found in previous studies without the imposition of a priori fixed geometry including an isotropic top layer (with anisotropy less than 1%) which is between 60 and 170 km thick, and separated into hemispheres with a slow west and a faster east. Strong anisotropy (with a maximum of 7.2%) is found mainly in the west, with much weaker anisotropy in the east. We observe for the first time that the western anisotropic zone is largely confined to the northern hemisphere, a property which would not be recognised in models assuming a simple hemispherical parameterisation. We further find that the inner most inner core, in which the slowest anisotropic velocity direction is tilted relative to Earth's axis of rotation (ζ=55∘±16∘), is offset by 400 km from the centre of the inner core and is restricted to the eastern hemisphere. We propose that this anomalous anisotropy might indicate the presence of a different phase of iron (either bcc or fcc) compared to the rest of the inner core (hcp). Published version This research was supported by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 681535 - ATUNE) and a Vici award number 016.160.310/526 from the Netherlands Organisation for Scientific Research (NWO). LW acknowledges support from a Discovery Early Career Research Award (project number DE170100329), funded by the Australian Government. 2022-12-21T06:16:13Z 2022-12-21T06:16:13Z 2022 Journal Article Brett, H., Hawkins, R., Waszek, L., Lythgoe, K. & Deuss, A. (2022). 3D transdimensional seismic tomography of the inner core. Earth and Planetary Science Letters, 593, 117688-. https://dx.doi.org/10.1016/j.epsl.2022.117688 0012-821X https://hdl.handle.net/10356/163899 10.1016/j.epsl.2022.117688 2-s2.0-85133459490 593 117688 en Earth and Planetary Science Letters © 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). application/pdf |
| spellingShingle | Science::Geology Inner Core Seismology Brett, Henry Hawkins, Rhy Waszek, Lauren Lythgoe, Karen Deuss, Arwen 3D transdimensional seismic tomography of the inner core |
| title | 3D transdimensional seismic tomography of the inner core |
| title_full | 3D transdimensional seismic tomography of the inner core |
| title_fullStr | 3D transdimensional seismic tomography of the inner core |
| title_full_unstemmed | 3D transdimensional seismic tomography of the inner core |
| title_short | 3D transdimensional seismic tomography of the inner core |
| title_sort | 3d transdimensional seismic tomography of the inner core |
| topic | Science::Geology Inner Core Seismology |
| url | https://hdl.handle.net/10356/163899 |
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