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  • 1
    Publication Date: 2002-01-01
    Description: The results of seismic investigations obtained for the Trans-European Suture Zone (TESZ) show the presence of relatively low velocity rocks (Vp 〈 6.1 kms-1), of sedimentary, metamorphic or volcanic origin, down to a depth of 20 km; high velocity (Vp = 6.8-7.3 kms-1) lower crust, the Moho at a depth of approximately 30-33 km; and a high-velocity (Vp 〉 8.3 kms -1) uppermost mantle. The transition of the crustal structure is seen across a 200 km wide zone. The three-layered crystalline crust of Baltica changes over this distance into the two-layered crust of Palaeozoic (Variscan) Europe, due to the disappearance of the lowest layer (Vp [~] 7.1 kms-1) and tapering off of the Baltican/cratonic wedge. The seismic profiles suggest that the lower crust (Vp [~] 7.1 kms-1) in the transition zone represents the attenuated Baltica margin underthrust towards the SW beneath the Avalonian accretionary wedge. The latter corresponds to the low-velocity upper crust (Vp 〈 6.1 kms-1) characteristic of the German-Polish Caledonides. Consequently, the high-velocity reflective lower crust of Baltica affinity extends approximately 200 km to the SW of the Teisseyre-Tornquist Zone within the basement of the Palaeozoic Platform. The Avalonian upper/middle crust is confined in the SW against the WNW-ESE trending Dolsk Fault. To the SW of the Odra Fault, a typical Variscan crust is detected which shows two-layer structure and relatively low P-wave velocities. The WNW-ESE Odra Fault, approximately parallel to the Dolsk Fault, splits the Variscan domain into the Variscan externides buried beneath the Palaeozoic Platform in the NE and the Variscan internides of the Sudetes in the SW. We interpret both the Odra and Dolsk Faults as dextral strike-slip features that cross cut the NE termination of the Variscan Orogen parallel to the Teisseyre-Tornquist Zone. In a relatively small area, they juxtapose three crustal domains representing, successively, the Variscan internides, externides and the Variscan foreland.
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  • 2
    Publication Date: 2015-11-27
    Description: The increasingly dense coverage of Europe with broad-band seismic stations makes it possible to image its lithospheric structure in great detail, provided that structural information can be extracted effectively from the very large volumes of data. We develop an automated technique for the measurement of interstation phase velocities of (earthquake-excited) fundamental-mode surface waves in very broad period ranges. We then apply the technique to all available broad-band data from permanent and temporary networks across Europe. In a new implementation of the classical two-station method, Rayleigh and Love dispersion curves are determined by cross-correlation of seismograms from a pair of stations. An elaborate filtering and windowing scheme is employed to enhance the target signal and makes possible a significantly broader frequency band of the measurements, compared to previous implementations of the method. The selection of acceptable phase-velocity measurements for each event is performed in the frequency domain, based on a number of fine-tuned quality criteria including a smoothness requirement. Between 5 and 3000 single-event dispersion measurements are averaged per interstation path in order to obtain robust, broad-band dispersion curves with error estimates. In total, around 63,000 Rayleigh- and 27,500 Love-wave dispersion curves between 10 and 350 s have been determined, with standard deviations lower than 2 per cent and standard errors lower than 0.5 per cent. Comparisons of phase-velocity measurements using events at opposite backazimuths and the examination of the variance of the phase-velocity curves are parts of the quality control. With the automated procedure, large data sets can be consistently and repeatedly measured using varying selection parameters. Comparison of average interstation dispersion curves obtained with different degrees of smoothness shows that rough perturbations do not systematically bias the average dispersion measurement. They can, therefore, be treated as random but they do need to be removed in order to reduce random errors of the measurements. Using our large new data set, we construct phase-velocity maps for central and northern Europe. According to checkerboard tests, the lateral resolution in central Europe is ≤150 km. Comparison of regional surface-wave tomography with independent data on sediment thickness in North-German Basin and Polish Trough confirms the high-resolution potential of our phase-velocity measurements. At longer periods, the structure of the lithosphere and asthenosphere around the Trans-European Suture Zone (TESZ) is seen clearly. The region of the Tornquist-Teisseyre-Zone in the southeast is associated with a stronger lateral contrast in lithospheric thickness, across the TESZ compared to the region across the Sorgenfrei-Tornquist-Zone in the northwest.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 3
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 4
    Publication Date: 2019-07-17
    Description: The aims of this study are the investigation of the Earth's structure and dynamics at the continental margin between the mid-Atlantic-ridge system (Mohns and Knipovich Ridges) and the Bear Island (Bjørnøya) region from its top sedimentary cover to its imprint in the upper mantle. In this region the margin includes an extremely thick sedimentary wedge and steep slopes, with at least one major paleo-fracture zone cutting through the wedge. Recent studies in this area indicate very low seismic velocities in the lithosphere and the stress field undergoes an extensional-compressional transition. It is therefore of particular interest to understand the structural architecture, the stress and the dynamics of the whole region because of its natural hazard exposure and the processes involved in the formation of the margin and the opening of the North Atlantic.To obtain such information, detailed monitoring and analysis of the seismicity between the margin and the mid-Atlantic ridges are necessary. To achieve this, deep seismic sounding data, as well as records from temporary broadband installations, supplementary to data from existing seismic stations in the region were collected. In autumn 2007, we began withseismological field experiments along the continental margin of the Barents Sea near Bear Island (Bjørnøya) and the Mohns and Knipovich Ridges. The field experiments comprise the installation and parallel operation of several seismic instruments during 2007-2008 such as 12 broadband Ocean Bottom Seismometers (OBSs), two new broadband seismometers, a small temporary seismic array with 13 sensors and active seismicrefraction/reflection experiments along two profiles crossing the region and recorded with additional short period OBSs and land stations.First results of the joint data analysis with respect to seismicity and crustal structure in the region of interest will be presented.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 5
    Publication Date: 2019-07-17
    Description: A 410 km long Ocean Bottom Seismometer profile spanning from the Bear Island, Barents Sea to oceanic crust formed along the Mohns Ridge has been modelled by use of ray-tracing with regard to observed P-waves. The northeastern part of the model represents typical continental crust, thinned from ca. 30 km thickness beneath the Bear Island to ca. 13 km within the Continent–Ocean-Transition. Between the Hornsund FZ and the Knølegga Fault, a 3–4 km thick sedimentary basin, dominantly of Permian/Carboniferous age, is modelled beneath the ca. 1.5 km thick layer of volcanics (Vestbakken Volcanic Province). The P-wave velocity in the 3–4 km thick lowermost continental crust is significantly higher than normal (ca. 7.5 km s–1). We interpret this layer as a mixture of mafic intrusions and continental crystalline blocks, dominantly related to the Paleocene-Early Eocene rifting event. The crystalline portion of the crust within the south-western part of the COT consists of a ca. 30 km wide and ca. 6 km thick high-velocity (7.3 km s–1) body. We interpret the body as a ridge of serpentinized peridotites. The magmatic portion of the ocean crust accreted along the Knipovich Ridge from continental break-up at ca. 35 Ma until ca. 20 Ma is 3–5 km thicker than normal. We interpret the increased magmatism as a passive response to the bending of this southernmost part of the Knipovich Ridge. The thickness of the magmatic portion of the crust formed along the Mohns Ridge at ca. 20 Ma decreases to ca. 3 km, which is normal for ultra slow spreading ridges.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 6
    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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  • 7
    Publication Date: 2019-07-17
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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  • 8
    Publication Date: 2019-07-17
    Description: Wide-angle seismic data acquired by use of air-guns and Ocean Bottom Seismometers (OBS) contain strong direct water arrivals and multiples, generally considered as noise and thus not included in the modelling. However, a recent study showed that standard ray-tracing modelling of the water multiples recorded off the Bear Island, North Atlantic, provided a reliable estimate of the velocity distribution in the water layer. Along the profile, the water velocity is found to change from about 1450 to approximately 1490 m/s. In the uppermost 400 m the velocities are in the range of 1455-1475 m/s, corresponding to the oceanic thermocline. In the deep ocean there is a velocity decrease with depth, and a minimum velocity of about 1450 m/s is reached at about 1.5 km depth. Below that, the velocity increases to about 1495 m/s at approximately 2.5 km depth. Here, we demonstrate that including the amplitudes in the modelling provide valuable information about the VP contrast at the seafloor, as well as the VP/VS ratio and attenuation (QP) of the uppermost sediments. The VP contrast at the seafloor is estimated at about 250 m/s, within a precision of approximately ±30 m/s. The VP/VS ratio in the uppermost sedimentary layer is modeled in the range 2.25-2.50, and the QP factor is estimated at 1000 for the water and 30-50 and 40-50 for the uppermost sediments. The values obtained for the sediments suggest a lithology dominated by silty clays, with porosity below average.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 9
  • 10
    Publication Date: 2019-07-16
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , NonPeerReviewed
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