(1) Geophysical Institute, Academy of Science of the Czech Republic, Prague
A passive teleseismic experiment (TOR), traversing the northern part of the Trans-European Suture Zone (TESZ) in Germany, Denmark and Sweden, recorded data for tomography of the upper mantle with a lateral resolution of few tens of km as well as for a detailed study of seismic anisotropy. A joint inversions of teleseismic P-residual spheres and shear-wave splitting parameters allows us to retrieve 3-D orientation of dipping anisotropic structures in different domains of the subcrustal lithosphere. We distinguish three major domains of different large-scale fabric divided by first-order sutures cutting the whole lithosphere thickness. The Baltic Shield north of the Sorgenfrei-Tornquist Zone (STZ) is characterised by lithosphere thickness around 175 km and the anisotropy is modelled by olivine aggregate of hexagonal symmetry with the high-velocity (a,c) foliation plane striking NW-SE and dipping to NE. Southward of the STZ, beneath the Norwegian-Danish Basin, the lithosphere thins abruptly to about 75 km. In this domain, between the STZ and the so-called Caledonian Deformation Front (CDF), the anisotropic structures strike NE-SW and the high-velocity (a,c) foliations dip to NW. To the south of the CDF, beneath northern Germany, we observe a heterogeneous lithosphere with variable thickness and anisotropic structures and with high velocities predominatly dipping to SW. Most of the anisotropy observed at TOR stations can be explained by preferred olivine orientations frozen in the subcrustal lithosphere. Beneath northern Germany, a part of the shear-wave splitting is probably caused by a present-day flow in the asthenosphere.
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