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S and P velocity heterogeneities within the upper mantle below the Baltic Shield
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. (Earthquake Seismology)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. (Earthquake Seismology)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
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2008 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 462, no 1-4, 109-124 p.Article in journal (Refereed) Published
Abstract [en]

Upper mantle structure beneath the Baltic (Fennoscandian) Shield is investigated using non-linear tomographic inversion of relative arrival-time residuals. 52 selected teleseismic earthquakes recorded by 45 broadband stations of the Swedish National Seismological Network (SNSN) provide 1532 good quality S-wave relative arrival times. SV and SH arrival-time residuals were initially analyzed independently, providing two separate models. These reveal several consistent major features, many of which are also consistent with P-wave results. Lateral velocity variations of ± 3–4% are observed to depths of at least 470 km. The correlation between the SH and SV models is investigated and shows a pattern of minor but significant differences down to around 150–200 km depth, below which the models are essentially similar. Direct cell by cell comparison of the model velocities reveals a similar pattern, with velocity differences between the models of up to 4%. Numerical tests show that differences in the two S-wave models can only be partially attributed to noise and limited resolution, and some features are attributed to the effect of large scale anisotropy. One of the significant and sharp discrepancies between the S models coincides with a presumed boundary between Archean and Proterozic domains, suggesting different anisotropic characteristics in the two regions.

Place, publisher, year, edition, pages
2008. Vol. 462, no 1-4, 109-124 p.
Keyword [en]
Teleseismic tomography; Lithosphere; Upper mantle structure beneath Baltic Shield; Seismic anisotropy
National Category
Geophysics
Research subject
Geophysics with specialization in Seismology
Identifiers
URN: urn:nbn:se:uu:diva-102100DOI: 10.1016/j.tecto.2008.02.015ISI: 000262240900010OAI: oai:DiVA.org:uu-102100DiVA: diva2:214217
Available from: 2009-05-04 Created: 2009-05-04 Last updated: 2013-04-23Bibliographically 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.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 653
Keyword
teleseismic tomography, mantle lithosphere, seismic anisotropy, teleseismic earthquakes, shear wave splitting
National Category
Earth and Related Environmental Sciences
Research subject
Geophysics Specialized In Seismology
Identifiers
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)
Opponent
Supervisors
Available from: 2009-05-18 Created: 2009-05-07 Last updated: 2009-05-25

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Shomali, Zaher HosseinRoberts, RolandHieronymus, Christoph F.Bödvarsson, Reynir

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