Crustal structure of the Mid-Polish Trough beneath the Teisseyre–Tornquist Zone seismic profile

Abstract

A new seismic refraction and wide-angle reflection experiment in the Teisseyre–Tornquist Zone (TTZ) in Poland was conducting during July 1993 as an international Polish, Finnish, German and Swedish co-operation. The TTZ profile running in an SE–NW direction was exactly located in the central part of the Mid-Polish Trough in the zone of maximum subsidence (from Upper Permian to Upper Cretaceous). 19 shot points were placed along the 450km profile. The interval between the shot points was about 25km. 31 explosions (90 to 1000kg of dynamite) were recorded in two deployments using 135 modern three-component seismic stations, with spacing of the recording sites of about 1.7km. In this area, the depth of the consolidated basement, with a velocity of about 5.7–5.8km/s, is 5 to 12km deep. Nevertheless, the P-wave velocity is very low (Vp<6.1km/s) down to depths of 15–20km. Below this complex, velocities of 6.5–6.6km/s and 6.9–7.2km/s were found and the thicknesses of the corresponding layers are 8–11km and 9–14km respectively. The total thickness of the crust varies from 35 to 41km. The results are discussed in combination with other seismic results from this region, which were obtained from deep seismic sounding and deep near-vertical reflection profiles as well as surface wave studies.