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  • 1995-1999  (5)
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  • 1
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: During the period 1961–1985, hundreds of nuclear explosions from the area of the Soviet Union and China were well recorded at Finnish seismological stations. The seismic waves recorded on the Baltic (Fennoscandian) shield penetrated through the mantle of the Siberian platform, the Ural Mountains and the East European platform. From the known crustal models, the functions describing the increase of the average velocities of sedimentary cover and crystalline complex of the crust with thickness were found. The corrections for sedimentary cover and crustal thickness were included. The large amount of data permitted the calculation of traveltimes of P waves for three sectors up to distances of about 5000 km. In all mantle models, the boundaries ‘400’and ‘700’km were found. Comparison of the results shows a difference in the traveltimes of the order of 5 s at a distance of about 4000 km, which reflects the mantle structure differentiation for depths greater than 700 km (lowest velocities for latitudinal direction and highest velocities for longitudinal direction). The average S-wave velocity model of the mantle was obtained using the traveltimes of S-wave first arrivals. High values of the VP/VS ratio were found in the depth interval 200–400 km, while in other depth intervals they were close to 1.73. Our 1-D models are compared with and discussed in connection with other models of the East European and Siberian platforms as well as with global tomographic solutions.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-1626
    Keywords: lithospheric structure ; dispersion ; surface waves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences , Physics
    Notes: Abstract Experimental dispersion curves of Rayleigh and Love waves along the Uppsala-Prague profile have been determined using records of several Italian earthquakes. To interpret the dispersion data, results of previous geophysical investigations in this region were first analyzed. Seven blocks of the crust and upper mantle were distinguished along the profile on the basis of deep seismic sounding and other seismic data. Layered models were proposed for these blocks. Computation of Rayleigh and Love waves shows a large differentiation of theoretical dispersion curves for the northern (Precambrian) and southern (Palaeozoic) part of the profile. A laterally inhomogeneous model for theUppsala - Prague profile, composed of the seven blocks, satisfies the surface wave data for the profile. Moreover, a mean layered model for the whole profile has also been proposed.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2020-02-12
    Description: The Trans-European Suture Zone (TESZ) comprises a series of sutures that developed by Palaeozoic amalgamation of the Phanerozoic Central Europe onto the Proterozoic Baltica and East European Plate during the formation of Pangea. Within TESZ, the Permian Basin in Poland froms the easternmost part of the Permian Central European Basin, which is bordered on the east by the East European Craton (EEC) and on the southwest by the Bohemian Massif. The axis of the basin, the Mid-Polish Trough, parallels the edge of the EEC. The Teisseyre-Tornquist Zone (TTZ) is a geological inversion zone in the Polish Trough. A large seismic experiment, the POLONAISE´97 project, was conducted in Poland during May of 1997 and targeted the deep structure of the TESZ and the complex series of upper crustal features associated with it. It included contributions from the geophysical communities in Poland, Denmark, the USA, Lithuania, Germany, Finland, Sweden and Canada. This large lithospheric seismic experiment deployed 613 instruments to record 64 shots along five profiles with a total length of about 2000 km. Moreover, five multichannel seismic reflection stations (90 and 120 channels) recorded all singnals from shots. Two dimensional velocity models were derived by P-wave tomographic inversion. These models provide an initial interpretation of this massive data set and allow us to present a few significant seismic and tectonic observations. One of the most important is a very distinct asymmetry between the maximum thickness of the sedimentary cover in the Polish Trough (16-20 km) and the crustal root (~50 km) associated with TESZ/TTZ.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 4
    Publication Date: 2020-02-12
    Description: During EUROBRIDGE"96 seismic data were acquired along a 544-km NW-SE profile, from the East Lithuanian Belt (EL) to the Ukrainian Shield. Explosive sources from 16 shotpoints at 30-km intervals were recorded by 114 three-component seismographs deployed at 3-4-km intervals along the profile. Tomographic inversion and raytrace modelling, integrated with results from the EUROBRIDGE"95 experiment, established a two-dimensional P-wave velocity lithospheric model and the spatial variation of Vp/Vs. Sedimentary cover in Belarus consists of two principal layers with P-wave velocities of about 2.3 and 4.0 km/s. Upper, middle and lower crystalline crust exhibit velocities of 6.1-6.3, 6.4-6.8 and 6.9-7.2 km/s, and are characterised by low velocity gradients and small contrasts at boundaries. The crust below Belarus is about 50 km thick with Moho elevations of a few kilometres. Mantle P-wave velocities immediately beneath the Moho are generally 8.2-8.4 km/s. A lower lithosphere reflector occurs at 65-70 km depth. S-wave velocities are high in the upper crust and low in the lower crust. Our crustal model shows similarities to results from Scandinavia. High lower-crustal velocities and a crustal thickness of about 50 km (common features of Proterozoic crust) are observed throughout the EUROBRIDGE"96 profile. The boundary between the EL and West Lithuanian Granulite Domain (WLG) is associated with pronounced crustal velocity changes, and a thinning of crust towards the northwest. The WLG may be part of a larger southern Baltic Sea tectonic unit. Correlation of our seismic structure with near-surface geology tentatively suggests that contact zones between the EL, Belarus-Baltic Granulite Domain, Central Belarussian Belt (CB), and the Osnitsk-Mikashevichi Igneous Belt all dip slightly to the southeast, consistent with successive docking of the terranes during craton growth. A spectacular feature of our model is high velocities throughout the CB crust, which marks the Fennoscandia-Sarmatia suture. Here we observe a change from typical shield/platform crust in the northwest to highly heterogeneous crust with pronounced lower crustal reflectivity in the southeast. Our results are consistent with CB uplift during continental collision. Our model implies significant tectonic involvement of middle crust in the formation of the Pripyat Trough.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 5
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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