A series of kinematic inversions based on robust non-linear optimization approach were performed using travel time data from a series of seismic refraction experiments: . These experiments were performed in Central Europe from 2000 were processed in this study. The goal of this work was to find seismic velocity models yielding travel times consistent with observed data.Optimum 2D inhomogeneous isotropic P-wave velocity models were computed. We have developed and used a specialized two-step inverse procedure. In the first "parametric" step, the velocity model contains interfaces whose shapes are defined by a number of parameters. The velocity along each interface is supposed to be constant but may be different along the upper and lower side of the interface. Linear vertical interpolation is used for points in between interfaces. All parameters are searched for using robust non-linear optimization (Differential Evolution algorithm). Rays are continuously traced by the bending technique. In the second "tomographic" step, smallscale velocity perturbations are introduced in a dense grid covering the currently obtained velocity model. Rays are fixed in this step. Final velocity models yield travel time residuals comparable to typical picking errors (RMS ~ 0.1 s).As a result, depth-velocity cross-sections of P waves along all processed profiles are obtained. The depth range of the models is 35 -50 km, the velocity varies in the range 3.5 -8.2 km/s. Lowest velocities are detected in near-surface depth sections crossing sedimentary formations. The middle crust is generally more homogeneous and has typical P wave velocity around 6 km/s. Surprisingly the lower crust is less homogeneous and the computed velocity is in the range 6.5 -7.5 km/s. The MOHO is detected in the depth 30 -45 km.

The refraction data from the SUDETES 2003 experiment were used for highresolution tomography along the profile S01. The S01 profile crosses the zone ErbendorfVohenstrauss (ZEV) near the KTB site, then follows the SW-NE oriented Eger Rift in the middle part and continues toward the NE across the Elbe zone and the Sudetic structures as far as the Trans-European Suture Zone. To get the best resolution in the velocity image only the first arrivals of Pg waves with minimum picking errors were used. The previous depth-recursive tomographic method, based on Claerbout's imaging principle, has been adapted to perform the linearized inversions in iterative mode. This innovative DRTG method (Depth-Recursive Tomography on Grid) uses a regular system of refraction rays covering uniformly the mapped domain. The DRTG iterations yielded a fine-grid velocity model with a required level of RMS travel-time fit and the model roughness. The traveltime residuals, assessed at single depth levels, were used to derive the statistical lateral resolution of ''lens-shaped'' velocity anomalies. Thus, for the 95% confidence level and 5% anomalies, one can resolve their lateral sizes from 15 to 40 km at the depths from 0 to 20 km. The DRTG tomography succeeded in resolving a significant low-velocity zone (LVZ) bound to the Franconian lineament nearby the KTB site. It is shown that the next optimization of the model best updated during the DRTG iterations tends to a minimumfeature model with sweeping out any LVZs. The velocities derived by the depth-recursive tomography relate to the horizontal directions of wave propagation rather than to the vertical. This was proved at the KTB site where pronounced anisotropic behavior of a steeply tilted metamorphic rock complex of the ZEV unit has been previously determined. Involving a *7% anisotropy observed for the ''slow'' axis of symmetry oriented coincidentally in the horizontal SW-NE direction of the S01 profile, the DRTG velocity model agrees fairly well with the log velocities at the KTB site. Comparison with the reflectivity map obtained on the reflection seismic profile KTB8502 confirmed the validity of DRTG velocity model at maximum depths of *16 km. The DRTG tomography enabled us to follow the relationship of major geological units of Bohemian Massif as they manifested in the obtained P-wave velocity image down to 15 km. Although the contact of Saxothuringian and the Teplá-Barrandian Unit (TBU) is collateral with the S01 profile direction, several major tectonic zones are rather perpendicular to the Variscan strike and so fairly imaged in the S01 cross-section. They exhibit a weak velocity gradient of sub-horizontal directions within the middle crust. In particular, the Moldanubian and TBU contact beneath the Western Krušné hory/Erzgebirge Pluton, the buried contact of the Lusatia unit and the TBU within the Elbe fault zone were identified. The maxima on the 6,100 ms -1 isovelocity in the middle crust delimitated the known ultrabasic Erbendorf complex and implied also two next ultrabasic massi...

[1] We study the azimuthal velocity variation of Pg waves in the Bohemian Massif using data collected during Central European Lithospheric Experiment Based on Refraction (CELEBRATION) 2000. We analyze travel times of waves generated by 28 shots and recorded by 256 portable and 19 permanent seismic stations deployed on the territory of the Czech Republic and in adjacent areas. We use recording offset ranging from 30 to 190 km with azimuths covering the whole interval of angles. The observed travel times are inverted for parameters of a velocity model formed by an isotropic low-velocity subsurface layer with a varying depth lying on a homogeneous transversely isotropic half-space with a horizontal axis of symmetry. The recovered velocity displays a systematic azimuthal variation indicating a regional-scale intrinsic or effective anisotropy in the Bohemian Massif. The mean, minimum and maximum values of the velocity are v mean = 6.03 km/s, v min = 5.98 km/s, v max = 6.10 km/s, respectively, indicating an anisotropy of 1.5-2.5%. The direction of the maximum propagation velocity is $N35°E being approximately perpendicular to the present maximum compression in the Earth crust in central Europe. The observed anisotropy cannot be induced by stress-aligned cracks in the crust, because the crack models predict azimuthal velocity variations completely inconsistent with the observed one. Therefore we suggest the crustal anisotropy to be induced by a preferred orientation of rock-forming minerals and large-scale intrusion fabrics developed during a tectonic evolution of the Bohemian Massif.

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