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  • 1
    Electronic Resource
    Electronic Resource
    Wave Diffraction In Multilayered Media With the Indirect Boundary Element Method: Application to 3-D Diffraction of Long-Period Surface Waves By 2-D Lithospheric Structures (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 125 (1996), S. 0 
    Details
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: An indirect boundary-element method is presented for simulating seismic wave diffraction in layered media with irregular interfaces. Recursive formulae are developed to take into account an arbitrary number of layers without increasing the size of the problem in terms of computer memory. the interfaces between layers are of variable geometry, and interfaces can be superposed to introduce horizontally finite structures. such as lenses or sedimentary basins. In the present implementation, we study three-dimensional (3-D) diffraction of plane waves by two-dimensional (2-D) structures. the formulation is nevertheless sufficiently general to include the complete 3-D case. Even though the method can be used at all scales, the main purpose of the theoretical development is to simulate diffraction of long-period surface waves by heterogeneous lithospheric structures. A new approach to treat incident surface waves in multilayered media is therefore developed, but other wave types, such as body-waves and internal seismic sources, can easily be introduced. the method is verified by transparency tests and comparison with other simulation methods. the application on the 3-D diffraction of plane Rayleigh waves by a major lithospheric boundary shows that significant conversions between wave types are present, and that the diffracted waves influence the apparent phase velocities measured at the surface above the heterogeneity and several wavelengths behind it.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-246X.1996.tb00017.x
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    On the possibility of anisotropy in the D'' layer as inferred from the polarization of diffracted S waves
    Amsterdam : Elsevier
    Physics of the Earth and Planetary Interiors 87 (1994), S. 1-32 
    Details
    ISSN: 0031-9201
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Geosciences , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1016/0031-9201(94)90019-1
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    Paper (German National Licenses)
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  • 3
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    Surface waves across 2-D structures: a method based on coupled local modes (1988)
    Oxford University Press
    Details
    Publication Date: 1988-04-01
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 4
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    Imaging anisotropic layering with Bayesian inversion of multiple data types (2016)
    Oxford University Press
    Details
    Publication Date: 2016-05-27
    Description: Azimuthal anisotropy is a powerful tool to reveal information about both the present structure and past evolution of the mantle. Anisotropic images of the upper mantle are usually obtained by analysing various types of seismic observables, such as surface wave dispersion curves or waveforms, SKS splitting data, or receiver functions. These different data types sample different volumes of the earth, they are sensitive to different length scales, and hence are associated with different levels of uncertainties. They are traditionally interpreted separately, and often result in incompatible models. We present a Bayesian inversion approach to jointly invert these different data types. Seismograms for SKS and P phases are directly inverted using a cross-convolution approach, thus avoiding intermediate processing steps, such as numerical deconvolution or computation of splitting parameters. Probabilistic 1-D profiles are obtained with a transdimensional Markov chain Monte Carlo scheme, in which the number of layers, as well as the presence or absence of anisotropy in each layer, are treated as unknown parameters. In this way, seismic anisotropy is only introduced if required by the data. The algorithm is used to resolve both isotropic and anisotropic layering down to a depth of 350 km beneath two seismic stations in North America in two different tectonic settings: the stable Canadian shield (station FFC) and the tectonically active southern Basin and Range Province (station TA-214A). In both cases, the lithosphere–asthenosphere boundary is clearly visible, and marked by a change in direction of the fast axis of anisotropy. Our study confirms that azimuthal anisotropy is a powerful tool for detecting layering in the upper mantle.
    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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  • 5
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    Insights in P- and S-wave relative traveltime tomography from analysing finite-frequency Frechet kernels (2015)
    Oxford University Press
    Details
    Publication Date: 2015-07-10
    Description: Regional body-wave tomography, also called ACH tomography, is the inversion of relative traveltime residuals of teleseismic body waves measured at regional networks. We analyse the characteristics of the finite-frequency Fréchet kernels for P and S waves for this kind of tomography. Using a simplified geometry enables us to use the complete Green's function in the expression of the Fréchet kernels and analyse elements, which are usually neglected, like the importance of the near-field terms and the P -wave traveltime sensitivity to shear wave velocity variations. By comparing the kernels of the relative residuals and absolute ones, we show that relative residuals have a reduced sensitivity to heterogeneities of large dimensions, and that this reduction is a generalization of the fact that the average model is not recovered in ACH tomography. This sensitivity reduction affects equally short- and long-period residuals. We show in addition the presence of a sensitivity reduction at large depth for the long-period waves. Kernels and reflectivity impulse responses of the crust are used to analyse if crustal corrections should be made frequency-dependent in finite-frequency regional tomography. We find that in most cases the frequency dependence due to reverberations is substantial, and that in many realistic network configurations ray theory is unlikely to be well appropriate to compute crustal corrections for the long-period waves. We also find that the lateral dimensions of the crust affecting the traveltimes is frequency dependent and reaches, at long periods, 50 km for sedimentary basins and 100 km for Moho depth.
    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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  • 6
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    Multiscale, finite-frequency P and S tomography of the upper mantle in the southwestern Fennoscandian Shield (2015)
    Oxford University Press
    Details
    Publication Date: 2015-04-25
    Description: We image the P - and S -wave structure of the upper mantle in southwestern Scandinavia using a wavelet-based, multiscale parametrization and finite-frequency theory to model wave propagation. Relative traveltime residuals of direct P and S waves are measured in a high- and low-frequency band and are corrected for crustal structure using a detailed model for the study area. A range of resolution tests are used to find optimal damping values not only for variations in V P and V S separately, but also for perturbations in their ratio V P / V S . The tests show that features down to a size of 100 (150) km can be well resolved in the P (S) tomography. To ease comparison with previous studies we also perform ray-theoretical multiscale tomographies, and to test the degree of vertical smearing we evaluate different parametrizations in the vertical direction (wavelet-based multiscale and convolutional quelling). Our finite-frequency, multiscale images of variations in V P and V S confirm the existence of low velocities below southern Norway and Denmark and high velocities beneath the shield proper in Sweden, as seen in previous studies, but add more details to this simplified picture. The low velocities below southern Norway and Denmark are confined to a channel-like structure at about 100–200 km depth, and the lateral transition from low to high velocities follows zones of Carboniferous-Permian extension and magmatism very closely. A deeper low-velocity anomaly below central southern Norway emerges from the channel at 150 km depth and extends to a depth of 350 km. In the Swedish area we infer high-velocity anomalies in V P and V S , and negative anomalies in V P / V S that indicate a strongly depleted mantle. We propose that the episodic erosion and convective removal of an originally thick mantle lithosphere below southern Norway to its current thickness of about 100 km could have been a trigger for episodic uplift in the Mesozoic and Cenozoic.
    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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  • 7
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    Surface wave tomography across the Sorgenfrei-Tornquist Zone, SW Scandinavia, using ambient noise and earthquake data (2015)
    Oxford University Press
    Details
    Publication Date: 2015-08-22
    Description: We produce a S -wave velocity model of the crust and upper mantle around the Sorgenfrei–Tornquist Zone, southern Scandinavia, by analysing ambient seismic noise and earthquake recordings on temporary and permanent regional network stations. In a first step, we perform tomographical inversion of surface wave dispersion data from seismic noise to obtain Rayleigh and Love wave phase-velocity maps from 3 to about 30 s period. Local dispersion curves are then combined with regionally averaged surface wave velocities from earthquake data measured between 15 and about 100 s period. Dispersion curves are jointly inverted for a 3-D model of the S -wave velocity and radial velocity anisotropy by using a combined Monte Carlo and linearized inversion approach. Results reveal significant crustal as well as uppermost mantle velocity variations at all depth levels. Upper crustal structural variations are mainly controlled by the thick sedimentary Danish Basin with both low S -wave velocities and high anisotropy. Despite of the known limited capability of surface wave inversion to constrain interface depths and model parameter trade-offs, obtained Moho depths are in good agreement with previous studies in the region. Marked crustal thinning is clearly revealed beneath the Danish Basin with a narrow transition to the thicker crust in Swedish shield areas. Despite very different crustal and morphological structures, Denmark and southern Norway both have similar well-defined upper-mantle low-velocity zones, interpreted as asthenosphere, starting a depth of about 100 km. Compared with southern Sweden, showing high upper-mantle velocities, characteristic for shields, velocities are reduced by 0.30–0.40 km s –1 (6–8 per cent) at the depth levels of 140–200 km and radial anisotropy of 2–4 per cent is observed. Our study confirms the importance of the Sorgenfrei–Tornquist Zone, as a very deep structural boundary, separating old, thick, cratonic Baltica lithosphere in southern Sweden from reworked and attenuated Baltica lithosphere in Denmark and southern Norway.
    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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  • 8
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    MAGNUS--A Seismological Broadband Experiment to Resolve Crustal and Upper Mantle Structure beneath the Southern Scandes Mountains in Norway (2010)
    Seismological Society of America
    Details
    Publication Date: 2010-01-01
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America
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  • 9
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    Measuring and crust-correcting finite-frequency travel time residuals – application to southwestern Scandinavia (2015)
    Copernicus
    Details
    Publication Date: 2015-07-01
    Description: We present a data processing routine to compute relative finite-frequency travel time residuals using a combination of the Iterative Cross-Correlation and Stack (ICCS) algorithm and the MultiChannel Cross-Correlation method (MCCC). The routine has been tailored for robust measurement of P and S wave travel times in several frequency bands and for avoiding cycle-skipping problems at the shortest periods. We also investigate the adequacy of ray theory to calculate crustal corrections for finite-frequency regional tomography in normal continental settings with non-thinned crust. We find that ray theory is valid for both P and S waves at all relevant frequencies as long as the crust does not contain low-velocity layers associated with sediments at the surface. Reverberations in the sediments perturb the arrival times of the S waves and the long-period P waves significantly, and need to be accounted for in crustal corrections. The data processing routine and crustal corrections are illustated using data from a network in southwestern Scandinavia.
    Electronic ISSN: 1869-9537
    Topics: Geosciences
    Published by Copernicus on behalf of European Geosciences Union.
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  • 10
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    The deep structure of the Scandes and its relation to tectonic history and present-day topography (2013)
    Elsevier
    Details
    Publication Date: 2013-08-01
    Print ISSN: 0040-1951
    Electronic ISSN: 1879-3266
    Topics: Geosciences , Physics
    Published by Elsevier
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