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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.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
    Publication Date: 2016-10-22
    Description: Phase velocities derived from ambient-noise cross-correlation are compared with phase velocities calculated from cross-correlations of waveform recordings of teleseismic earthquakes whose epicentres are approximately on the station–station great circle. The comparison is conducted both for Rayleigh and Love waves using over 1000 station pairs in central Europe. We describe in detail our signal-processing method which allows for automated processing of large amounts of data. Ambient-noise data are collected in the 5–80 s period range, whereas teleseismic data are available between about 8 and 250 s, resulting in a broad common period range between 8 and 80 s. At intermediate periods around 30 s and for shorter interstation distances, phase velocities measured from ambient noise are on average between 0.5 per cent and 1.5 per cent lower than those observed via the earthquake-based method. This discrepancy is small compared to typical phase-velocity heterogeneities (10 per cent peak-to-peak or more) observed in this period range.We nevertheless conduct a suite of synthetic tests to evaluate whether known biases in ambient-noise cross-correlation measurements could account for this discrepancy; we specifically evaluate the effects of heterogeneities in source distribution, of azimuthal anisotropy in surface-wave velocity and of the presence of near-field, rather than far-field only, sources of seismic noise. We find that these effects can be quite important comparing individual station pairs. The systematic discrepancy is presumably due to a combination of factors, related to differences in sensitivity of earthquake versus noise data to lateral heterogeneity. The data sets from both methods are used to create some preliminary tomographic maps that are characterized by velocity heterogeneities of similar amplitude and pattern, confirming the overall agreement between the two measurement methods.
    Keywords: Seismology
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 3
    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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  • 4
    Publication Date: 2016-01-17
    Description: The increasingly dense coverage of Europe with permanent and temporary broadband seismic stations makes it possible to image its lithosphere and asthenosphere structure in great detail, provided that structural information can be extracted effectively from the very large volumes of data. 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. Between 5 and 3000 single-event dispersion measurements are averaged per inter-station path in order to obtain robust, broad-band dispersion curves with error estimates. In total, around 63000 Rayleigh- and 27500 Love-wave dispersion curves between 10 s and 350 s have been determined, with standard deviations lower than 2 % and standard errors lower than 0.5 %. Using our large new dataset, we construct phase-velocity maps for central and northern Europe. According to checkerboard tests, the lateral resolution in central Europe is ≤ 150 km. The new, broad-band, phase-velocity dataset offers abundant, valuable information on the structure of the crust and upper mantle beneath Europe. In our contribution we present and discuss results, which shed new light on the lithosphere-asthenosphere structure across the Transeuropean Suture Zone spanning from the Variscan European Platform towards the Proterozoic East European Platform. Comparison of regional surface-wave tomography with independent data on sediment thickness in North-German Basin and Polish Trough (from a compilation of deep seismic sounding results) confirms the accuracy of the imaging using our short-period, phase-velocity measurements. The region of the Tornquist- Teisseyre Zone is associated with a stronger lateral contrast in the lithospheric thickness from the East European Platform towards the southwest compared to the region across the Sorgenfrei-Tornquist Zone as can be clearly seen from the longer periods.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Conference , NonPeerReviewed
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  • 5
    Publication Date: 2013-09-25
    Description: We apply automated two-station broadband phase velocity dispersion measurements to all available broadband data from permanent seismic stations in Europe, as available through the European Integrated Data Archive (EIDA, http://www.orfeus-eu.org/eida/) infrastructure. As part of our quality control we detect several typical patterns in our measurements that can be related to technical problems, incorrect metadata information or uncover inconsistencies in data processing routines. These effects include timing and various response issues, most prominently erroneous response information. Our procedure is thus able to identify potentially problematic (meta)data from a large set of seismic data and offers an applicable way to increase data quality at data centers.
    Print ISSN: 1680-7340
    Electronic ISSN: 1680-7359
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 6
    Publication Date: 2019-02-01
    Description: The upper crust of central Europe preserves a mosaic of tectonic blocks brought together by the Caledonian and Variscan Orogenies. The lower crust, in contrast, appears to have undergone extensive reworking: the flat Moho across broad areas and the absence of contrasts in seismic properties across tectonic boundaries suggest that the Moho and lower crust are, effectively, younger than the upper crust. The evolution of the mantle lithosphere below the Moho has been particularly difficult to constrain. In this paper, we use seismic, geological and geochemical evidence to show that central Europe's mantle lithosphere has evolved continuously throughout the Mesozoic and Cenozoic Eras, with episodes of lithospheric thinning causing surface uplift and volcanism and lithospheric thickening - subsidence and sedimentation. High-resolution surface wave tomography reveals a strong spatial correlation between locations of recent basaltic volcanism and currently thin lithosphere. We infer that intraplate volcanism further back in the geological past is also an indication of lithospheric thinning at the time. The north-central Europe's lithosphere was, thus, thinned at the time of the Permian volcanism, with its subsequent, Post-Permian cooling and thickening causing the subsidence and sedimentation in the North German and neighboring basins. This explains the presence of Permian volcanics atop presently thickened lithosphere. South of these basins, lithospheric thinning (evidenced by seismic data) is associated with the volcanism of the Central European Cenozoic Igneous Province and surface uplift. Thin lithosphere here also correlates spatially with high melting rates, high silica contents, high temperatures and shallow magma generation. This synthesis highlights the dynamic nature of the lithosphere-asthenosphere boundary beneath central Europe and, more generally, Phanerozoic continents. The boundary's depth varies in time; its deepening (lithospheric cooling and thickening) causes subsidence and sedimentation; its shallowing (lithospheric thinning by thermal erosion or delamination) is marked with uplift and intraplate volcanism.
    Type: Article , PeerReviewed
    Format: text
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