Seismic velocity model of the crust and upper mantle along profile PANCAKE across the Carpathians between the Pannonian Basin and the East European Craton

- The WARR survey was carried out in Ukraine and Hungary crossing Carpathians.
- P- and S-wave velocity model was constructed using ray-tracing forward modelling.
- The thickness of the crust along the profile varies from 20 to 48 km.
- A significant change in Moho topography is observed beneath the Carpathians.
- Full waveform synthetic sections were calculated to support the velocity model.

Results are presented of a seismic wide-angle reflection/refraction survey along a profile between the Pannonian Basin (PB) and the East European Craton (EEC) called PANCAKE. The P- and S-wave velocity model derived can be divided into three sectors: the PB; the Carpathians, including the Transcarpathian Depression and the Carpathian Foredeep; and the south-western part of the EEC, including the Trans European Suture Zone (TESZ). Seismic data support a robust model of the Vp velocity structure of the crust. In the PB, the 22-23 km thick crust consists of a 2-5 km thick sedimentary layer (Vp = 2.4-3.7 km/s), 17-20 km thick upper crystalline crust (5.9-6.3 km/s) and an up to 3 km thick lower crustal layer (Vp = 6.4 km/s). In the central part of the Carpathians, a 10-24 km thick uppermost part of the crust with Vp ≤ 6.0 km/s may correspond to sedimentary rocks of different ages; several high velocity bodies (Vp = 5.35, 5.95 and 6.05 km/s) within the sedimentary flysch sequences may represent volcanic sequences. The Moho depth changes from 25 km to 45 km over ca. 100 km distance beneath the Carpathians, west of TESZ. The cratonic crust has a typical three layer structure with a pronounced thickening of the lower crust towards the Ukrainian Shield, where a high velocity lower crust (Vp > 7.2 km/s) is observed. Two low-velocity lenses in the upper crust of the EEC are interpreted beneath major sedimentary troughs (Lviv and Volyn-Podolsk). Mantle reflectors are observed at depths of ~ 45 km and ~ 75 km below the PB and 10-20 km below the Moho in the EEC. Sub-Moho (Pn) velocities increase from 8.0 km/s beneath the PB to 8.1 km/s beneath the Carpathians and to ~ 8.3 km/s beneath the EEC. S-waves of acceptable quality are recorded in the EEC; their signal-to-noise ratios increase towards the Ukrainian Shield.