uu.seUppsala University Publications
Change search
ReferencesLink to record
Permanent link

Direct link
Effects of seismic anisotropy on P-velocity tomography of the Baltic Shield
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
GFU, Prague.
GFU, Prague.
GFU, Prague.
Show others and affiliations
2012 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 188, no 2, 600-612 p.Article in journal (Refereed) Published
Abstract [en]

We investigate possible effects of neglecting seismic anisotropy on standard isotropic P-velocity tomographic images of the upper mantle beneath the Baltic shield. Isotropic inversions of teleseismic P- and S-wave traveltimes exhibit alternating high- and low-velocity heterogeneities down to depths of over 400 km. Differences in tomographic inversions of SV- and SH-wave traveltimes are distinct down to depths of about 200 km and are associated with anisotropy of the lithospheric mantle. Anisotropic structures of the upper mantle affect both the P and S traveltimes, shear-wave splitting as well as the P polarization directions. Joint inversion for isotropic and anisotropic velocity perturbations is not feasible due to the limited 3-D ray coverage of available data. Therefore, we correct the input traveltimes for anisotropic contributions derived from independent analyses and then perform standard isotropic inversions. These corrections are derived either directly from directional deviations of P-wave propagation or are calculated in anisotropic models retrieved by joint inversions of body-wave anisotropic parameters (P-residual spheres and shear-wave splitting). These anisotropic models are also used to fit backazimuth variations of P-wave polarization directions. General features of tomographic images calculated from the original and the anisotropy-corrected data are similar. Amplitudes of the velocity perturbations decrease below similar to 200 km depth, that is in the sub-lithospheric mantle. In general, large-scale anisotropy related to the fabrics of the continental mantle lithosphere can contaminate tomographic images in some parts of models and should not be ignored.

Place, publisher, year, edition, pages
2012. Vol. 188, no 2, 600-612 p.
Keyword [en]
Body waves, Seismic anisotropy, Seismic tomography, Cratons
National Category
Earth and Related Environmental Sciences
URN: urn:nbn:se:uu:diva-102497DOI: 10.1111/j.1365-246X.2011.05280.xISI: 000298840800016OAI: oai:DiVA.org:uu-102497DiVA: diva2:216257
Available from: 2009-05-07 Created: 2009-05-07 Last updated: 2012-02-15Bibliographically approved
In thesis
1. Isotropic and Anisotropic P and S Velocities of the Baltic Shield Mantle: Results from Analyses of Teleseismic Body Waves
Open this publication in new window or tab >>Isotropic and Anisotropic P and S Velocities of the Baltic Shield Mantle: Results from Analyses of Teleseismic Body Waves
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The upper mantle structure of Swedish part of Baltic Shield with its isotropic and anisotropic seismic velocity characteristics is investigated using telesesismic body waves (i.e. P waves and shear waves) recorded by the Swedish National Seismological Network (SNSN).

Nonlinear high-resolution P and SV and SH wave isotropic tomographic inversions reveal velocity perturbations of ± 3 % down to at least 470 km below the network. Separate SV and SV models indicate several consistent major features, many of which are also consistent with P-wave results. A direct cell by cell comparison of SH and SV models reveals velocity differences of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially caused by noise and limited resolution, and some features are attributed to the effect of large scale anisotropy.

Shear-wave splitting and P-travel time residual analyses also detect anisotropic mantle structure. Distinct back-azimuth dependence of SKS splitting excludes single-layer anisotropy models with horizontal symmetry axes for the whole region. Joint inversion using both the P and S data reveals 3D self-consistent anisotropic models with well-defined mantle lithospheric domains. These domains of differently oriented anisotropy most probably retain fossil fabric since the domains' origin, supporting the idea of the existence of an early form of plate tectonics during formation of continental cratons already in the Archean.

The possible disturbing effects of anisotropy on seismic tomography studies are investigated, and found to be potentially significant. P-wave arrival times were adjusted based on the estimates of mantle anisotropy, and re-inverted. The general pattern of the velocity-perturbation images was similar but changed significantly in some places, including the disappearance of a slab-like structure identified in the inversion with the original data. Thus the analysis demonstrates that anisotropy of quite plausible magnitude can have a significant effect on the tomographic images, and should not be ignored. If, as we believe, our estimates of anisotropy are reasonably correct, then the model based on the adjusted data should give a more robust and correct image of the mantle structure.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 110 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 653
teleseismic tomography, mantle lithosphere, seismic anisotropy, teleseismic earthquakes, shear wave splitting
National Category
Earth and Related Environmental Sciences
Research subject
Geophysics Specialized In Seismology
urn:nbn:se:uu:diva-102501 (URN)978-91-554-7548-2 (ISBN)
Public defence
2009-06-12, Hambergsalen, Geocentrum, Villavägen 16, SE-752 36 Uppsala, Sweden, Uppsala, 13:00 (English)
Available from: 2009-05-18 Created: 2009-05-07 Last updated: 2009-05-25

Open Access in DiVA

No full text

Other links

Publisher's full text

Search in DiVA

By author/editor
Roberts, RolandShomali, HosseinBödvarsson, Reynir
By organisation
In the same journal
Geophysical Journal International
Earth and Related Environmental Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 281 hits
ReferencesLink to record
Permanent link

Direct link