The Trans-European Suture Zone (TESZ) comprises a series of sutures that developed by Palaeozoic amalgamation of the Phanerozoic Central Europe onto the Proterozoic Baltica and East European Plate during the formation of Pangea. Within TESZ, the Permian Basin in Poland forms the easternmost part of the Permian Central European Basin, which is bordered on the east by the East European Craton (EEC) and on the southwest by the Bohemian Massif. The axis of the basin, the Mid-Polish Trough, parallels the edge of the EEC. The Teisseyre-Tornquist Zone (TTZ) is a geological inversion zone in the Polish Trough. A large seismic experiment, the POLONAISE'97 project, was conducted in Poland during May of 1997 and targeted the deep structure of the TESZ and the complex series of upper crustal features associated with it. It included contributions from the geophysical communities in Poland, Denmark, the USA, Lithuania, Germany, Finland, Sweden and Canada. This large lithospheric seismic experiment deployed 613 instruments to record 64 shots along five profiles with a total length of about 2000 km. Moreover, five multichannel seismic reflection stations (90 and 120 channels) recorded all signals from shots. Two dimensional velocity models were derived by P-wave tomographic inversion. These models provide an initial interpretation of this massive data set and allow us to present a few significant seismic and tectonic observations. One of the most important is a very distinct asymmetry between the maximum thickness of the sedimentary cover in the Perish Trough (16-20 km) and the crustal root (similar to 50 km) associated with TESZ:TTZ.