P- and S-wave velocity model of the southwestern margin of the Precambrian East European Craton; POLONAISE'97, profile P3

The large-scale seismic experiment POLONAISE'97 investigated the seismic structure of the crust and the uppermost mantle in the Polish region of the Trans-European Suture Zone. This paper covers the interpretation of seismic data along the 300-km-long P3 profile, which is located in the Precambrian East European Craton (EEC) parallel to the Teisseyre-Tornquist Zone. The recordings were of high quality, with seismic energy detectable out to 300 km offsets. The crustal model developed by two-dimensional raytracing forward modelling and waveform analysis is characterized by a subhorizontal uniform structure, although the boundaries of several large basement features are crossed. The crystalline crust consists of three parts: the upper, middle and lower crust with P-wave velocities of 6.1-6.4 km/s, 6.55-6.7 km/s and 7.05-7.15 km/s respectively. The P(m)P wave can usually be correlated at distances beginning at about 100 km, but it has variable reflection character. Moho depth increases from 38 km at the NW end of the profile to 44 km at the SE end. The P(n) velocity of 8.05-8.1 km/s is less than that previously found in neighbouring areas of the EEC. The V(P)/V(S) ratio was determined separately for the upper/middle and lower crust to be 1.67 and 1.77 respectively. Following the P(n) wave, another phase with an apparent velocity of about 8.3 km/s is interpreted as a weak reflection from a low-contrast discontinuity in the uppermost mantle. (C) 1999 Elsevier Science B.V. All rights reserved.