(1) Geophysical Institute, Academy
of Science of the Czech Republic, Prague
(2) EOST - Institut de Physique du
Globe Strasbourg, France
The study of deep structure of the lithosphere of the Bohemian Massif (BM) by means of seismic anisotropy is based on teleseismic body wave observations and on a joint inversion of anisotropic data (P-residual spheres, the fast shear-wave polarisations and split times). We observe that velocity anomalies are strongly affected by different ori-entations of dipping anisotropic structures within the mantle lithosphere. There are distinct lateral variations of the pattern of P-residual spheres as well as of the split time dt and orientation of the fast shear waves. While in the central part of the BM a large dt and a general E-W orientation of the fast split wave prevail, in the eastern part the dt is smaller and the fast polarisation rotates to the WNW-ESE direction. The mantle lithosphere of the BM appears to consist of at least three domains with dif-ferent orientation of the large-scale fabric. The domains, which we interpret by 3D self-consistent anisotropic models, are separated by sutures cutting the whole litho-sphere. In our research we put special emphasis on the western part of the BM. The region is characterised by the well known earthquake swarms concentrated mainly within the brittle part of the upper crust above the crossing of the deep suture be-tween the Saxothuringian (S) and the Moldanubian (M) with the tectonically active Marianske Lazne (ML) fault. In the mantle lithosphere of both units we observe di-vergently oriented anisotropic structures with typical shear-wave splittings around 1 s or more. Near the deep suture beneath the centre of the swarm near Novy Kostel we observe decreased anisotropy which can be caused by a weakened fabric of the mantle lithosphere. An international seismic field experiment BOHEMA (BOhemian Massif HEterogeneity and Anisotropy) has been running in the region since October 2001. It aims at studying the structure and processes in the crust and upper mantle by means of integrated seismic tomography.
Not available.