The TTZ-South seismic profile follows the Teisseyre-Tornquist zone (TTZ) at the SW margin of the East European craton (EEC). Investigation results reveal the upper lithospheric structure as representing the NW-vergent, NE-SW striking overthrust-type, Paleoproterozoic (~1.84–1.8 Ga) Fennoscandia-Sarmatia suture. The Sarmatian segment of the EEC comprises two crustal-scale tectonic thrust slices: the Moldavo-Podolian and Lublino-Volhynian basement units, overriding the northerly located Lysogoro-Radomian unit of Fennoscandian affinity. The combined results of the TTZ-South and other nearby deep seismic profiles are consistent with a continuation of the EEC cratonic basement across the TTZ to the SW and its plunging into the deep substratum of the adjacent Paleozoic platform. Extensional deformation responsible for the formation of the mid to late Proterozoic (~1.4–0.6 Ga), SW-NE trending Orsha-Volhynia rift basin is probably also recorded. The thick Ediacaran succession deposited in the rift was later tectonically thickened due to Variscan deformation. The Moho depth varies between 37 and 49 km, resulting in the thinnest crust in the SE, sharp depth changes across the TTZ, and slow shallowing from 49 to 43 km to the NW. The abrupt Moho depth increase from 43 to 49 km is considered to reflect the overlying lower crust tectonic duplication within the suture zone.

The wide-angle reflection and refraction (WARR) TTZ-South transect carried out in 2018 crosses the SW region of Ukraine and the SE region of Poland. The TTZ-South profile targeted the structure of the Earth’s crust and upper mantle of the Trans-European Suture Zone, as well as the southwestern segment of the East European Craton (slope of the Ukrainian Shield). The ~550 km long profile (~230 km in Poland and ~320 km in western Ukraine) is an extension of previously realized projects in Poland, TTZ (1993) and CEL03 (2000). The deep seismic sounding study along the TTZ-South profile using TEXAN and DATA-CUBE seismic stations (320 units) made it possible to obtain high-quality seismic records from eleven shot points (six in Ukraine and five in Poland). This paper presents a smooth P-wave velocity model based on first-arrival travel-time inversion using the FAST (First Arrival Seismic Tomography) code. The obtained image represents a preliminary velocity model which, according to the P-wave velocities, consists of a sedimentary layer and the crystalline crust that could comprise upper, middle and lower crustal layers. The Moho interface, approximated by the 7.5 km/s isoline, is located at 45—47 km depth in the central part of the profile, shallowing to 40 and 37 km depth in the northern (Radom-Łysogóry Unit, Poland) and southern (Volyno-Podolian Monocline, Ukraine) segments of the profile, respectively. A peculiar feature of the velocity cross-section is a number of high-velocity bodies distinguished in the depth range of 10—35 km. Such high-velocity bodies were detected previously in the crust of the Radom-Łysogóry Unit. These bodies, inferred at depths of 10—35 km, could be allochthonous fragments of what was originally a single mafic body or separate mafic bodies intruded into the crust during the break-up of Rodinia in the Neoproterozoic, which was accompanied by considerable rifting. The manifestations of such magmatism are known in the NE part of the Volyno-Podolian Monocline, where the Vendian trap formation occurs at the surface.

The paper presents information about the seismic experiment “AniMaLS” which aims to provide a new insight into the crust and upper mantle structure beneath the Polish Sudetes (NE margin of the Variscan orogen). The seismic network composed of 23 temporary broadband stations was operated continuously for about 2 years (October 2017 to October 2019). The dataset was complemented by records from eight permanent stations located in the study area and in the vicinity. The stations were deployed with an inter-station spacing of approximately 25–30 km. As a result, recordings of local, regional and teleseismic events were obtained. We describe the aims and motivation of the project, the station deployment procedure, as well as the characteristics of the temporary seismic network and of the permanent stations. Furthermore, this paper includes a description of important issues like data transmission setup, status monitoring systems, data quality control, near-surface geological structure beneath stations and related site effects, etc. Special attention was paid to verification of correct orientation of the sensors. The obtained dataset will be analysed using several seismic interpretation methods, including analysis of seismic anisotropy parameters, with the objective of extending knowledge about the lithospheric and sublithospheric structure and the tectonic evolution of the study area.

Crustal and uppermost mantle structure along the Teisseyre-Tornquist Zone (TTZ)  was explored along the ~550 km long, NW-SE-trending TTZ-South profile, using seismic wide-angle reflection/refraction (WARR) method. The profile line was intended to follow the border between the East European Craton (EEC) and the so called Palaeozoic Platform (PP) of north-central Europe, believed to contain a number of crustal blocks that were accreted to the craton during pre-late Carboniferous times, defining the Trans-European Suture Zone (TESZ).The seismic velocity model of the TTZ-South profile shows lateral variations in crustal structure. Its Ukrainian segment crosses the interior of the Sarmatian segment of the EEC, where the crystalline basement gradually dips from ~2 km depth in the SE to ~12 km at the Ukrainian-Polish border. This part of the model shows a four-layered crustal structure, with an up to 15 km-thick sedimentary cover, an underlying crystalline upper crust, a 10-15 km-thick middle crust and a ~15 km thick lower crust. In Poland, the profile passes along the TESZ/EEC transition zone of complex crustal structure. The crystalline basement, whose top occurs at depths of 10-17 km, separates the sedimentary cover from the ~10 km thick mid-crustal layer (Vp=6.5-6.6 km/s), which, in turn, overlies a block of 10-15 km thickness with upper crustal velocities (Vp~6.2 km/s). The latter is underlain by a ~10-15 km-thick lower crust. Along most of the model one can see conspicuous velocity inversion zones occuring at various depths. At intersections of the TTZ-South profile with some previous deep seismic profiles (e.g. CEL02, CEL05, CEL14, PANCAKE) such inversions document complex wedging relationships between the EEC and PP crustal units. These may have resulted from tectonic compression and thick-skinned thrusting due to either Neoproterozoic EEC collision with accreting terranes or intense Variscan orogenic events. Five high velocity bodies (HVB; Vp = 6.85-7.2 km/s) were detected in the middle and lower crust at 15-37 km depth. The Moho depth varies substantially along the profile. It is at ~42 km depth in the NW and deepens SE-ward to ~50 km at ~685 km. Subsequently, it rises abruptly to ~43 km at the border of the Sarmatian segment of the EEC and sinks again to ~50 km beneath the Lviv Paleozoic trough at ~785 km. From this point until the SE end of the profile, the Moho gently shallows, up to a depth of ~37 km, including a step-like jump of 2 km at ~875 km. Such abrupt Moho steps may be related to crust-scale strike-slip faults. Along the whole profile, sub-Moho velocities are ~8.05-8.1 km/s, and at depths of 57-63 km Vp values reach 8.2-8.25 km/s. Four reflectors/refractors were modelled in the upper mantle at ~57-65 km and ~80 km depths.

Carried out in 2021, the wide-angle reflection-refraction (WARR) SHIELD’21 profile crosses, from SW to NE, the main tectonic structures of Ukraine. It has targeted the crustal and uppermost mantle structure underlying the Archaean and Paleoproterozoic crystalline complexes of the Ukrainian Shield and the adjacent platformal areas. To the SW of the Ukrainian Shield, the crystalline basement is overlain by Vendian through Paleozoic strata of the Volhyno-Podolian Homocline, plunging at its SW end below the Carpathian belt and its Neogene foredeep. To the NE, the crystalline cratonic basement is covered by Devonian and Carboniferous successions of the Dnieper-Donets rift basin. The ~650 km long SHIELD’21 profile is a northeasterly extension of the RomUkrSeis profile carried out in 2014 and running from Romania to the southwestern part of the Ukrainian Shield (Starostenko et al., 2020). The WARR study along the SHIELD’21 profile provided high-quality seismic records. The main recorded seismic waves are refractions of P- and S-waves in the sedimentary layer, crystalline basement, middle and lower crust and uppermost mantle, as well as reflections from crustal boundaries, the Moho interface and boundaries in the uppermost mantle. The correlation picking of their arrival times allowed us to build a velocity model not only for the P-, but also for S-waves and Vp/Vs ratio. The model reveals that over the entire thickness of the crust, the Vp in the crystalline basement nowhere exceeds 6.85 km/s, which – particularly in the context of the lower crust – represent low values, but similar to those known from the other nearby deep seismic profiles (e.g. TTZ-South, and DOBRE-4). Patterns of crustal boundaries combined with velocity differences across them, permit hypothesizing on Proterozoic large-scale subhorizontal extensional faulting in the crystalline upper crust. A prominent dome-like structure in the lower crust may represent a longitudinal section of a major duplex resulting from Paleoproterozoic overthrusting to the NW, comparable to those interpreted on the TTZ-South profile (Janik et al., 2022). The Moho shows strong variability of a depth (~32-50 km), and is underplated by lenticular horizontal ca. 10 km thick high velocity mantle bodies with Vp>8.36 to 8.40 km/s, also present deeper in the upper mantle of Vp between 8.15 and 8.25 km/s. The Moho is prominent and marked by the Vp velocity contrast of c. 1.4 to 1.8 km/s between the upper mantle and lower crust. It is characteristically undulated with successive downward and upward bends, with the amplitude locally exceeding 15 km and wavelength of the order of 150 to 250 km. A similar Moho undulation form was described along the DOBRE-4 profile and was interpreted as Mesozoic(?) buckle mega-folds (Starostenko et al, 2013). Janik, T. et al. (2022). TTZ-South, Minerals, 12, 112, doi.org/10.3390/min12020112 Starostenko, V. et al. (2013). DOBRE-4, Geophys. J. Int. 195, 740–766, doi.10.1093/gji/ggt292 Starostenko, V. et al. (2020). RomUkrSeis, Tectonophysics, 794, 228620, doi.org/10.1016/j.tec to.2020.228620

The paper presents information about the seismic experiment AniMaLS which aims to provide a new insight into the crustal and upper mantle structure beneath the Polish Sudetes (NE margin of the Variscan orogen). The seismic array composed of 23 temporary broadband stations was operating continuously for ~2 years (October 2017 and October 2019). The dataset was complemented by records from 8 permanent stations located in the study area and in the vicinity. The stations were deployed with inter-station spacing of approximately 25–30 km. As a result, good quality recordings of local, regional and teleseismic events were obtained. We describe the aims and motivation of the project, the stations deployment procedure, as well as the characteristics of the temporary seismic array and of the permanent stations. Furthermore, this paper includes a description of important issues like: data transmission set-up, status monitoring systems, data quality control, near-surface geological structure beneath stations and related site effects etc. Special attention was paid to verification of correct orientation of the sensors. The obtained data set will be modelled using several seismic interpretation methods, including analysis of seismic anisotropy parameters, with the objective of extending knowledge about the lithospheric and sub-lithospheric structure and the tectonic evolution of the study area.