LAMINATED STRUCTURE OF THE LOWER CRUST IN THE FORE-SUDETIC REGION IN POLAND, DERIVED FROM SEISMIC DATA

The results of seismic studies of the crust of the Palaeozoic Platform in the fore-Sudetic region, southwestem Poland, are presented. The structure of the sedimentary cover and the boundary of the consolidated basement were determined from refraction profiles of a total length of about 1500 km and from seismic velocity profiling in deep boreholes. Interpretation of data from deep seismic sounding and wide-angle reflection studies provided information on the structure of the lower crust and the crust-upper mantle transition zone. The results of the first deep seismic sounding measurements by the near-vertical profiling method, with recordings up to 18 s, are also reported. In the region under study, the sedimentary cover thickness ranges from 3 to about 13 km, and the Moho discontinuity depth is from 28 to 35 km. In the sedimentary cover and in the lower crust strong structural and physical inhomogeneities were identified. In the 23-34 km depth range, layers of 1-3 km thickness of increased and decreased velocity alternate. They have velocity contrasts of 0.4-0.7 km s-1 and are shown by intense sequences of reflected waves, which are observed both in the wide-angle reflection studies and in the near-vertical profiles.