Upper mantle seismic model of central Europe (including the alpine orogen) based on seismic events from the Lubin Copper Basin

The Lubin Copper Basin in Poland is situated in the vicinity of the Trans-European Suture Zone, in the region of the Variscan orogen. It is characterized by high seismicity, mainly induced by mining. The epicentral location is particularly suitable for the determination of lithospheric velocity structure for the two tectonic units in Central Europe: Alpine orogen and Variscides. We analyze traveltime curves constructed on the basis of the P-wave arrival times reported by European stations and listed in the International Seismic Bulletins for the period 1985-2000. The dense azimuthal coverage of the stations situated around the Alps and in the Variscides enables the determination of 1-D velocity structure down to 180 km depth. Corrections for origin times, focal depths and station elevation were applied. The main featur e visible in the obtained traveltime and velocity-depth distributions is the considerable difference in the upper mantle seismic structure between the two tectonic regions. The delay of P-wave arrivals is by about 3 s larger at the Alpine stations than at the stations located in the Variscides. We attribute this delay to differences between "fast" and "slow" structures in the "cold" and "hot" upper mantle, respectively. The 8° discontinuity can be clearly distin guished in the proposed models by a distinct delay at the offsets around 800-900 km from the source.