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  • 1
    Publication Date: 2019
    Description: 〈span〉〈div〉SUMMARY〈/div〉Extracting Moho-reflected 〈span〉P〈/span〉 waves from vertical component seismic noise to determine crustal thickness has become a common method over the last years. In this study, we image the reflectivity below various stations across Central and Eastern Europe and extract Moho-reflected 〈span〉S〈/span〉 waves using horizontal component correlations. In addition to horizontal component autocorrelations, we include single-station cross-correlations in the process of obtaining crustal thickness estimates from seismic noise for the first time. For each station, a lag time range for the reflectivity change associated with the Moho is obtained with the help of prior information, and lag times are converted to depth to give a crustal thickness range. In addition, we calculate 〈span〉vP〈/span〉/〈span〉vS〈/span〉 ratios from the picked reflectivity changes on the vertical and horizontal component correlations.On an average 8.5 months of data are needed for the autocorrelations to obtain stable results. For the cross-correlations, on average 1.3 yr of data are required to reach stability. The obtained Moho depth ranges compare well with results determined with vertical component autocorrelations, receiver functions and provided in the European Moho depth map. The 〈span〉vP〈/span〉/〈span〉vS〈/span〉 ratios show a large variability and do not give reliable results. In addition to identifying reflectivity changes in 〈span〉S〈/span〉 waves on the horizontal component correlations, it is also possible to observe these reflectivity changes on vertical component correlations, as well as 〈span〉P〈/span〉-wave reflectivity changes on the horizontal component correlations, for some stations. Furthermore, we can detect 〈span〉P〈/span〉- to 〈span〉S〈/span〉- or 〈span〉S〈/span〉- to 〈span〉P〈/span〉-converted phases on cross-correlations of mixed horizontal and vertical components. From this we conclude that the incidence of the waves reaching the surface is not generally vertical, leading to errors when converting lag time to depth and in the calculation of the 〈span〉vP〈/span〉/〈span〉vS〈/span〉 ratios. Lag time differences between the Moho arrivals on the two horizontal component autocorrelations can be interpreted in terms of azimuthal anisotropy in the crust.〈/span〉
    Print ISSN: 2051-1965
    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: 2019
    Description: 〈span〉Seismic interferometryseismic noisebody wavescrust〈/span〉
    Print ISSN: 2051-1965
    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: 2019
    Description: 〈span〉〈div〉Abstract〈/div〉We evaluate methods to estimate the global seismic moment rate of a planet from the k≥1 largest events observed during a limited and possibly short‐time span, as can be expected, for example, for lander missions to Mars. The feasibility of the approach is demonstrated with a temporary broadband seismometer that was recording in the Mojave desert, California, for 86 days in 2014, and by application to the Global Centroid Moment Tensor (CMT) catalog, subsets thereof, and a catalog of stable continental regions seismicity. From the largest event observed at Goldstone alone (Mw≈7.9), we estimate the Earth’s global moment rate to be 1.03×1022  N·m/yr, whereas an estimation based on the 10 strongest events yields a rate of 5.79×1021  N·m/yr. Summation of 42 yr of Global CMT solutions results in an average of 7.61×1021  N·m/yr. In general, a 2 yr interval of Global CMT solutions is sufficient to estimate the Earth’s annual moment rate to within a factor of 5 or better. A series of numerical experiments with more than 560 million synthetic catalogs based on the tapered Gutenberg–Richter distribution shows that the estimation is rather insensitive against an unknown slope of the distribution, and that bias and variance of the estimator depend on the ratio between moment rate and corner moment of the size frequency distribution. Moment rates of published Mars models differ by a factor of 1000 or more. Tests with simulated catalogs show that it will be possible to reject some of these models with data returned by NASA’s InSight mission after two years of nominal mission life time.〈/span〉
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 4
    Publication Date: 2014-04-16
    Description: The Mohorovičić discontinuity, Moho for short, which marks the boundary between crust and mantle, is the main first-order structure within the lithosphere. Geodynamics and tectonic evolution determine its depth level and properties. Here, we present a map of the Moho in central Europe across the Teisseyre-Tornquist Zone, a region for which a number of previous studies are available. Our results are based on homogeneous and consistent processing of P - and S -receiver functions for the largest passive seismological data set in this region yet, consisting of more than 40 000 receiver functions from almost 500 station. Besides, we also provide new results for the crustal v P / v S ratio for the whole area. Our results are in good agreement with previous, more localized receiver function studies, as well as with the interpretation of seismic profiles, while at the same time resolving a higher level of detail than previous maps covering the area, for example regarding the Eifel Plume region, Rhine Graben and northern Alps. The close correspondence with the seismic data regarding crustal structure also increases confidence in use of the data in crustal corrections and the imaging of deeper structure, for which no independent seismic information is available. In addition to the pronounced, stepwise transition from crustal thicknesses of 30 km in Phanerozoic Europe to more than 45 beneath the East European Craton, we can distinguish other terrane boundaries based on Moho depth as well as average crustal v P / v S ratio and Moho phase amplitudes. The terranes with distinct crustal properties span a wide range of ages, from Palaeoproterozoic in Lithuania to Cenozoic in the Alps, reflecting the complex tectonic history of Europe. Crustal thickness and properties in the study area are also markedly influenced by tectonic overprinting, for example the formation of the Central European Basin System, and the European Cenozoic Rift System. In the areas affected by Cenozoic rifting and volcanism, thinning of the crust corresponds to lithospheric updoming reported in recent surface wave and S -receiver function studies, as expected for thermally induced deformation. The same correlation applies for crustal thickening, not only across the Trans-European Suture Zone, but also within the southern part of the Bohemian Massif. A high Poisson's ratio of 0.27 is obtained for the craton, which is consistent with a thick mafic lower crust. In contrast, we typically find Poisson's ratios around 0.25 for Phanerozoic Europe outside of deep sedimentary basins. Mapping of the thickness of the shallowest crustal layer, that is low-velocity sediments or weathered rock, indicates values in excess of 6 km for the most pronounced basins in the study area, while thicknesses of less than 4 km are found within the craton, central Germany and most of the Czech Republic.
    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
    Publication Date: 2019
    Print ISSN: 2051-1965
    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
    Publication Date: 2019
    Description: 〈span〉〈div〉Summary〈/div〉Extracting Moho-reflected 〈span〉P〈/span〉-waves from vertical component seismic noise to determine crustal thickness has become a common method over the last years. In this study, we image the reflectivity below various stations across Central and Eastern Europe and extract Moho-reflected 〈span〉S〈/span〉-waves using horizontal component correlations. In addition to horizontal component autocorrelations, we include single-station cross-correlations in the process of obtaining crustal thickness estimates from seismic noise for the first time. For each station, a lag time range for the reflectivity change associated with the Moho is obtained with the help of prior information, and lag times are converted to depth to give a crustal thickness range. In addition, we calculate 〈span〉v〈/span〉〈sub〉P〈/sub〉/〈span〉v〈/span〉〈sub〉S〈/sub〉-ratios from the picked reflectivity changes on the vertical and horizontal component correlations. On average 8.5 months of data are needed for the autocorrelations to obtain stable results. For the cross-correlations, on average 1.3 yr of data are required to reach stability. The obtained Moho depth ranges compare well with results determined with vertical component autocorrelations, receiver functions, and provided in the European Moho depth map. The 〈span〉v〈/span〉〈sub〉P〈/sub〉/〈span〉v〈/span〉〈sub〉S〈/sub〉-ratios show a large variability and do not give reliable results. In addition to identifying reflectivity changes in 〈span〉S〈/span〉-waves on the horizontal component correlations, it is also possible to observe these reflectivity changes on vertical component correlations, as well as 〈span〉P〈/span〉-wave reflectivity changes on the horizontal component correlations, for some stations. Furthermore, we can detect 〈span〉P〈/span〉- to 〈span〉S〈/span〉- or 〈span〉S〈/span〉- to 〈span〉P〈/span〉-converted phases on cross-correlations of mixed horizontal and vertical components. From this we conclude that the incidence of the waves reaching the surface is not generally vertical, leading to errors when converting lag time to depth and in the calculation of the 〈span〉v〈/span〉〈sub〉P〈/sub〉/〈span〉v〈/span〉〈sub〉S〈/sub〉-ratios. Lag time differences between the Moho arrivals on the two horizontal component autocorrelations can be interpreted in terms of azimuthal anisotropy in the crust.〈/span〉
    Print ISSN: 2051-1965
    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
    Publication Date: 2012-12-19
    Description: The knowledge of the local soil structure is important for the assessment of seismic hazards. A widespread, but time-consuming technique to retrieve the parameters of the local underground is the drilling of boreholes. Another way to obtain the shear wave velocity profile at a given location is the inversion of surface wave dispersion curves. To ensure a good resolution for both superficial and deeper layers, the used dispersion curves need to cover a wide frequency range. This wide frequency range can be obtained using several arrays of seismic sensors or a single array comprising a large number of sensors. Consequently, these measurements are time-consuming. A simpler alternative is provided by the use of the ellipticity of Rayleigh waves. The frequency dependence of the ellipticity is tightly linked to the shear wave velocity profile. Furthermore, it can be measured using a single seismic sensor. As soil structures obtained by scaling of a given model exhibit the same ellipticity curve, any inversion of the ellipticity curve alone will be ambiguous. Therefore, additional measurements which fix the absolute value of the shear wave velocity profile at some points have to be included in the inversion process. Small-scale spatial autocorrelation measurements or MASW measurements can provide the needed data. Using a theoretical soil structure, we show which parts of the ellipticity curve have to be included in the inversion process to get a reliable result and which parts can be omitted. Furthermore, the use of autocorrelation or high-frequency dispersion curves will be highlighted. The resulting guidelines for inversions including ellipticity data are then applied to real data measurements collected at 14 different sites during the European NERIES project. It is found that the results are in good agreement with dispersion curve measurements. Furthermore, the method can help in identifying the mode of Rayleigh waves in dispersion curve measurements.
    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
    Publication Date: 2018-06-20
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 9
    Publication Date: 2017-11-07
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
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  • 10
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