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Introduction. The TTZ-South experiment is the latest in a series of three wide-angle reflection/refraction (WARR) seismic studies situated along a NW-SE oriented line in Central Europe. This paper presents the results of a WARR study on the ~550 km long УДК 550.341

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.

<p>The southern Baltic Sea area is in the transition zone between the Fennoscandian Shield as part of the East European Craton (EEC) and the West European Platform. This area is characterised by a mosaic of various geological blocks separated by several fault zones formed throughout the Phanerozoic. The most prominent tectonic feature is the NW–SE trending Sorgenfrei-Tornquist Zone, crossing the southern Baltic Sea area between Scania in Sweden and Pomerania in Poland. Recently, this area was covered with the new multi-channel seismic data (MCS), acquired during the “BalTec” cruise of the German R/V Maria S. Merian. In addition to MCS data, hydroacoustic and gravity data were collected along the same profiles.</p> <p>The new data, acquired during the “BalTec” cruise in 2016, include 3500 km of MCS data and 7000 km of gravity data. This is the first such a regional survey in the southern Baltic Sea, which provides a gapless image of sedimentary layer with a high resolution from seafloor to the base of Permian salt (North German-Polish Basin) or Palaeozoic strata (EEC). In addition, a 230-km long refraction/wide-angle reflection (WARR) profile was acquired across the transition zone to image its deeper structure. This profile is nearly parallel to the western Polish coast in half a distance to Bornholm.</p> <p>The main topic of our study is the structure of Phanerozoic sedimentary cover in the southern Baltic Sea and its relationship to the geological evolution of the area situated at the junction of two major tectonic units of NW Europe. In the methodological part of our research, we are going to develop the process of integration of potential field modelling into seismic interpretation workflow. Another important point is testing the capability of marine versus satellite gravity data to reflect the geometry of shallow tectonic structures.</p> <p>The first step in analysis of potential field data was integration of marine gravity with a regional gravity dataset. The result was a coherent gravity grid, which was used for further advanced processing, involving calculation of transformations and derivatives. We also included a regional magnetic grid in the advanced processing. Calculated derivatives and filters of gravity and magnetic data were applied for qualitative interpretation, i.e., compilation of a structural map based on the location and nature of gravity and magnetic anomalies. In addition, a preliminary 2D forward model was produced for the WARR profile to provide an image of the broad crustal structure. The next 2D models will be built upon seismic reflection profiles acquired during the “BalTec” cruise. The results will be eventually used to calibrate the three-dimensional model for the top of crystalline basement derived from gravity inversion.</p> <p>This study was funded by the Polish National Science Centre grant no UMO-2017/25/B/ST10/01348.</p>

<p>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).</p><p>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; V<sub>p</sub> = 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.</p>

Abstract. 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.

<p>Defining a transition zone between the Precambrian East European Craton (EEC) and the Palaeozoic West European Platform (WEP) is still a matter of discussion despite a large body of geophysical and geological data. The main tectonic feature of the transition zone is the Teisseyre-Tornquist Zone (TTZ), which has been variously interpreted over the past decades mainly because of a thick (c. 10 km) Palaeozoic and Mesozoic sedimentary cover masking its crustal architecture.  We investigated the crustal structure of the TTZ using a 270-km long wide-angle reflection/refraction profile (WARR) measured along 15 ocean-bottom seismometers and 2 land stations during the course of the RV MARIA S. MERIAN expedition ‘MSM52’. This NE to SW profile is oriented nearly parallel to the Polish coast, located ~ 48 km south of the Danish island of Bornholm. We prepared a two-dimensional gravity and magnetic forward model along this profile, using the Geosoft GM-SYS software with layers of infinite length. The basis for the potential field modelling is a seismic velocity model that has been prepared through trial-and-error forward modelling.</p><p>The seismic velocity model shows a continuity of the lower and middle crust of the EEC towards the basement of the WEP. The synthetic magnetic profile is smooth and indicates that the seismic data accurately revealed the geometry and depth of the magnetic (crystalline) basement. However, the model was unable to replicate short-wavelength, high-amplitude magnetic anomalies in the ENE section of the profile, probably representing iron oxide mineralisation in the crystalline basement of the EEC. The gravity model shows 3 areas of misfit between the synthetic and observed gravity profile. The most prominent misfit coincides with the NE boundary of the TTZ. To remedy the misfit, we produced two alternative gravity models that deviate from the seismic velocity model in the problematic area. One model postulates a crustal keel underneath the NE section of the TTZ and the other suggests the presence of a middle crust magmatic intrusion. Both models equally and adequately reduce the misfit of the gravity model.</p><p>Our models suggest a SW-ward continuation of the Baltica middle and lower crust through the TTZ and seem to preclude the coincidence of the Caledonian Thor suture with the TTZ. An important perturbation of the upper crust and sedimentary cover within the latter is mostly associated with the superimposed effects of Devonian-Carboniferous and Permian-Mesozoic extension. The only conspicuous compressional event confirmed by our data is the Late Cretaceous-Paleogene inversion of the Permian-Mesozoic basin. Due to limited resolution, our models did not reveal the effects of Caledonian nor Variscan shortening, including the Caledonian Deformation Front.<br><br><span>This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316.</span></p>

<p>Carried out in 2021, the wide-angle reflection and refraction (WARR) SHIELD’21<strong> </strong>profile crosses, from SW to NE, the main tectonic structures of Ukraine. It targeted the structure of the Earth’s crust and upper mantle of the southwestern margin of the East European Craton with overlying Neogene Carpathian Foredeep and Vendian-Paleozoic Volyn-Podolian Monocline, Archaean and Paleoproterozoic segments of Ukrainian Shield and Late Paleozoic Dnipro-Donetsk Basin. The ~650 km long SHIELD’21 profile is an extension of previously realized RomUkrSeis profile carried out in 2014 and running from the Apuseni Mountains to the southwestern Ukrainian Shield (Starostenko et al., 2020). The WARR study along the SHIELD’21 profile using TEXAN and DATA-CUBE short-period seismic stations provided high-quality seismic records. The field work was performed during the summer of 2021, included the deployment of autonomous seismic stations and drilling-explosive works. A total of 264 seismic receivers were involved, (160 DATA-CUBE and 104 TEXAN stations). The average spacing between observation points is about 2.65 km. The sampling interval for all stations was 0.01 s. Seismic energy was generated at 10 shot points (SP) with total charge in all wells 5775 kg. The distance between the SPs was about 50 km.</p> <p>The main recorded seismic waves are the refractions of P- and S- waves in sediments, basement, crust and uppermost mantle, and reflections from crustal boundaries, Moho interface and boundaries in the uppermost mantle. The correlation picking of their arrival times will allow to build a velocity model not only for P-, but also for S-waves and Vp/Vs ratio.</p> <p>The main objective of the SHIELD’21 project is to get new seismic data that increase our knowledge on the lithosphere structure and geodynamics of the study region.</p> <p> </p> <p>Starostenko, V., Janik, T., Mocanu, V., Stephenson, R., Yegorova, T., Amashukeli, T., Czuba, W., Środa, P., Murovskaya, A., Kolomiyets, K., Lysynchuk, D., Okoń, J., Dragut, A., Omelchenko, V., Legostaieva, O., Gryn, D., Mechie, J., & Tolkunov, A. (2020). RomUkrSeis: Seismic model of the crust and upper mantle across the Eastern Carpathians — From the Apuseni Mountains to the Ukrainian Shield. Tectonophysics, 794, 228620. https://doi.org/10.1016/j.tec to.2020.228620</p>