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Upper-mantle structure of the Baltic Shield below the Swedish National Seismological Network (SNSN) resolved by teleseismic tomography
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.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
2007 (English)In: Geophysical Journal International, ISSN 0956-540X, E-ISSN 1365-246X, Vol. 169, no 2, 617-630 p.Article in journal (Refereed) Published
Abstract [en]

Upper-mantle structure under the Baltic Shield is studied using non-linear high resolution teleseismic P-phase tomography. Observed relative arrival-time residuals from 52 teleseismic earthquakes recorded by the Swedish National Seismological Network (SNSN) are inverted to delineate the structure of the upper mantle. The network consists of 47 (currently working) three-component broad-band stations located in an area about 450 km wide and 1450 km long. In order to reduce complications due to possible significant three-dimensionality of Earth structure, events chosen for this study lay close to in-line with the long-axis of the array  (±30°) . Results indicate P-wave velocity perturbations of ±3 per cent down to at least 470 km below the network. The size of the array allows inversion for structures even at greater depths, and lateral variations of velocity at depths of up to 680 km appear to be resolved. Below the central part of the array (60°–64° N), where ray coverage is best, the data reveals a large region of relatively low velocity at depths of over about 300 km. At depths less than about 250–300 km, the models include a number of features, including an apparent slab-like structure dipping gently towards the north.

Place, publisher, year, edition, pages
2007. Vol. 169, no 2, 617-630 p.
Keyword [en]
ACH method, Baltic Shield, lithosphere, teleseismic tomography
National Category
Earth and Related Environmental Sciences
Research subject
Geophysics with specialization in Seismology
Identifiers
URN: urn:nbn:se:uu:diva-14359DOI: 10.1111/j.1365-246X.2007.03351.xISI: 000245675000022OAI: oai:DiVA.org:uu-14359DiVA: diva2:42129
Available from: 2008-01-30 Created: 2008-01-30 Last updated: 2017-12-11Bibliographically 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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