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  • Articles  (47)
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  • 1
    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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  • 2
  • 3
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: During the third Polish Antarctic Geodynamical Expedition in 1987-88, deep seismic sounding measurements were performed in the transition zone between the Drake plate and the Antarctic plate in West Antarctica. 30 shots were fired in the sea along profile DSS-17 of 310 km length. The interpretation was made with the use of seismic records of four land stations in the South Shetland Islands and Antarctic Peninsula. The interpretation yielded a 2-D model of the lithosphere down to 80 km depth. The crustal structure beneath the trough of Bransfield Strait is highly anomalous. The presence of a high-velocity body, with longitudinal seismic wave velocities vp〉7.0 km s-1, was detected in the 6-30 km depth range. This in-homogeneity was interpreted as an intrusion, coinciding with the Deception-Penguin-Bridgeman volcanic line. The Moho boundary depth ranges from 10 km in the South Shetland Trench area to 40 km under the Antarctic Peninsula. In the transition zone from the Drake Passage to the South Shetland Islands, a seismic boundary in the lower lithosphere occurs at a depth ranging from 35 to 80 km. The dip of both the Moho and this boundary is approximately 25d̀, and indicates the direction of subduction of the lithosphere of the Drake plate under the Antarctic plate. The results obtained were compared with earlier results of seismic, gravity and magnetic surveys in West Antarctica. A scheme of geotectonic division and a geodynamical model of the zone of subduction of the Drake plate under the Antarctic plate is compared with subduction zones in other areas of the circum-Pacific belt.
    Type of Medium: Electronic Resource
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  • 6
    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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  • 7
    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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  • 8
    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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  • 9
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 10
    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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