International Geologiical Congress - Oslo 2008

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EIL-06 Seismic anisotropy and deformation of the crust and mantle

 

Seismic 3D velocity modelling of the crust in southern and central Finland - indications of seismic anisotropy

 

Tellervo Hyv÷nen, University of Helsinki (Finland)
Timo Tiira, University of Helsinki (Finland)
Annakaisa Korja, University of Helsinki (Finland)
Kari Komminaho, University of Helsinki (Finland)
Pekka Heikkinen, University of Helsinki (Finland)
 

 

Local seismic tomography method was used to image the terrane distribution within the central parts of the Svecofennian Orogen in southern and central Finland. Three-dimensional crustal P- and S-wave velocity models were inverted and a Vp/Vs ratio model was calculated.

The modelling used Pg- and Sg-wave travel time data: from local events recorded by the SVEKALAPKO seismic tomography array, from controlled seismic shots recorded at portable stations, and non-controlled chemical explosions recorded at permanent seismic stations.

The lateral variation is more notable for Vp (5.9-6.6 km s-1) than for Vs (3.5-3.8 km s-1) in the upper 20 km of the crust. The Vp/Vs fluctuation is spatially more distinct than Vp, from 1.70 to 174 in the upper crust and from 1.72 to 1.78 in the lower crust. Thus, the tomography modelling reveals several crustal blocks within the Svekalapko area. These comprise granitoid areas surrounded by schist belts and their continuations at depth. The anisotropy the upper crust of the blocks is studied using directional means of P-wave residuals after the tomography inversion.

 

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