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Mapping crustal shear wave velocity structure and radial anisotropy beneath West Antarctica using seismic ambient noise

O'Donnell, J.P.; Brisbourne, A.M.; Stuart, G.W.; Dunham, C.K.; Yang, Y.; Nield, G.A.; Whitehouse, P.L.; Nyblade, A.A.; Wiens, D.A.; Anandakrishnan, S.; Aster, R.C.; Huerta, A.D.; Lloyd, A.J.; Wilson, T.; Winberry, J.P.

Mapping crustal shear wave velocity structure and radial anisotropy beneath West Antarctica using seismic ambient noise Thumbnail


Authors

J.P. O'Donnell

A.M. Brisbourne

G.W. Stuart

C.K. Dunham

Y. Yang

A.A. Nyblade

D.A. Wiens

S. Anandakrishnan

R.C. Aster

A.D. Huerta

A.J. Lloyd

T. Wilson

J.P. Winberry



Abstract

Using 8‐25s period Rayleigh and Love wave phase velocity dispersion data extracted from seismic ambient noise, we (i) model the 3D shear wave velocity structure of the West Antarctic crust and (ii) map variations in crustal radial anisotropy. Enhanced regional resolution is offered by the UK Antarctic Seismic Network. In the West Antarctic Rift System (WARS), a ridge of crust ~26‐30km thick extending south from Marie Byrd Land separates domains of more extended crust (~22km thick) in the Ross and Amundsen Sea Embayments, suggesting along‐strike variability in the Cenozoic evolution of the WARS. The southern margin of the WARS is defined along the southern Transantarctic Mountains (TAM) and Haag Nunataks‐Ellsworth Whitmore Mountains (HEW) block by a sharp crustal thickness gradient. Crust ~35‐40km is modelled beneath the Haag Nunataks‐Ellsworth Mountains, decreasing to ~30‐32km km thick beneath the Whitmore Mountains, reflecting distinct structural domains within the composite HEW block. Our analysis suggests that the lower crust and potentially the mid crust is positively radially anisotropic (VSH > VSV) across West Antarctica. The strongest anisotropic signature is observed in the HEW block, emphasising its unique provenance amongst West Antarctica's crustal units, and conceivably reflects a ~13km thick metasedimentary succession atop Precambrian metamorphic basement. Positive radial anisotropy in the WARS crust is consistent with observations in extensional settings, and likely reflects the lattice‐preferred orientation of minerals such as mica and amphibole by extensional deformation. Our observations support a contention that anisotropy may be ubiquitous in continental crust.

Citation

O'Donnell, J., Brisbourne, A., Stuart, G., Dunham, C., Yang, Y., Nield, G., …Winberry, J. (2019). Mapping crustal shear wave velocity structure and radial anisotropy beneath West Antarctica using seismic ambient noise. Geochemistry, Geophysics, Geosystems, 20(11), 5014-5037. https://doi.org/10.1029/2019gc008459

Journal Article Type Article
Acceptance Date Sep 3, 2019
Online Publication Date Nov 14, 2019
Publication Date Nov 30, 2019
Deposit Date Oct 14, 2019
Publicly Available Date May 14, 2020
Journal Geochemistry, Geophysics, Geosystems
Publisher American Geophysical Union
Peer Reviewed Peer Reviewed
Volume 20
Issue 11
Pages 5014-5037
DOI https://doi.org/10.1029/2019gc008459

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Copyright Statement
O'Donnell, J.P., Brisbourne, A.M., Stuart, G.W., Dunham, C.K., Yang, Y., Nield, G.A., Whitehouse, P.L., Nyblade, A.A., Wiens, D.A., Anandakrishnan, S., Aster, R.C., Huerta, A.D., Lloyd, A.J., Wilson, T. & Winberry, J.P. (2019). Mapping crustal shear wave velocity structure and radial anisotropy beneath West Antarctica using seismic ambient noise. Geochemistry, Geophysics, Geosystems 20(11): 5014-5037. 10.1029/2019GC008459. To view the published open abstract, go to https://doi.org/ and enter the DOI.






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