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  • 1
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    A proper methodology aimed at surface wave tomography (2006)
    Details
    Publication Date: 2019-11-04
    Description: When applying a methodology for obtaining the 3D shear-wave velocity structure of a medium from surface wave dispersion data, the problem must be considered with caution since one inverts path-averaged velocities and the use of any inversion method entails some drawbacks such as lack of uniqueness, unwarranted stability and constraints affecting the data. In order to avoid the application of consecutive inversions and to overcome these drawbacks, we propose alternative mapping methods, for example spatial prediction methods, or else the use of an algorithm that, from a mathematical viewpoint, can be understood through the application of the orthogonal projection theorem onto convex sets (POCS). Among the first ones, we try inverse weighted distance interpolation. The POCS algorithm we have used discretises a second order differential equation for the velocity field with boundary conditions. All these imaging techniques aimed at volumetric modelling and the visualisation of data are discussed, and finally we show some results based on ray path velocities obtained previously by inversion of phase and group velocities of Rayleigh waves propagating across the Iberian peninsula.
    Description: JCR Journal
    Description: open
    Keywords: Iberian peninsula ; gridding techniques ; POCS algorithm ; tomographic images ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 4117139 bytes
    Format: application/pdf
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  • 2
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    Preliminary objective regionalization of the Mediterranean basin derived from surface-wave tomography (2006)
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    Publication Date: 2019-11-04
    Description: An objective regionalization of the Mediterranean basin is derived from a tomographic study based on the fundamental mode of Rayleigh waves. The database is formed by seismic wavetrains recorded at very-broadband stations belonging to MedNet and other cooperative stations, located in the Mediterranean area. The data treatment consists of application of spectral filtering techniques aimed to determine path-averaged group velocities, computation of local group velocity maps for some periods and classification of the studied area in several homogeneous regions according to Principal Component Analysis (PCA) and Average Linkage (AL) algorithms. Finally, the group velocity dispersion curves representing each homogeneous region are compared and possible correlation between these regions and seismotectonic and structural characteristics are discussed.
    Description: JCR Journal
    Description: open
    Keywords: Mediterranean basin ; Rayleigh waves ; local group velocities ; clustering algorithms ; 04. Solid Earth::04.06. Seismology::04.06.99. General or miscellaneous ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 4360548 bytes
    Format: application/pdf
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  • 3
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    Construction of regional and local seismic anisotropic structures from wide-angle seismic data: Crustal deformation in the southeast of China (2008)
    Springer
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    Publication Date: 2008-09-04
    Description: We present a method to obtain spatial distributions of seismic anisotropy associated with regional stress and local faulting in the crust from wide-angle seismic data. The method contains three steps. The first step consists of obtaining radial- and transverse-component seismic sections using a pre-stack depth migration algorithm from the S-wave velocity model determined by conventional interpretation of picked intra-crustal seismic events. In the second step, we compute time delays between split shear-waves and polarizations of fast split shear-waves by minimizing the transverse-component seismic energy. The time delay and polarization in each layer are derived using a layer-stripping method. The final step is to estimate the average splitting parameters along the whole profile. Thus, the average time delay and polarization can be regarded as caused by the effects owing to regional structure and stress fields, whereas the residual values of the splitting parameters are considered to be related to local structures and local faulting. Our method allows us to construct multi-layer anisotropic images, which may later be interpreted in terms of intra-layer coupling/decoupling or deformation. We present results from a set of three-component seismic data acquired by a controlled source experiment in the southeast region of China. The results demonstrate that the average polarizations and time delays are consistent with the direction and strength of the stress field, and their lateral variations related to local anisotropy match the spatial distribution of surface faulting crossing the acquisition seismic profile. © Springer Science+Business Media B.V. 2008.
    Print ISSN: 1383-4649
    Electronic ISSN: 1573-157X
    Topics: Geosciences , Physics
    Published by Springer
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  • 4
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    Seismicity pattern of the Betic Cordillera (Southern Spain) derived from the fractal properties of earthquakes and faults (2010)
    Springer
    Details
    Publication Date: 2010-08-01
    Print ISSN: 1674-4519
    Electronic ISSN: 1867-8777
    Topics: Geosciences
    Published by Springer
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  • 5
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    Chaotic system detection of weak seismic signals (2009)
    Oxford University Press
    Details
    Publication Date: 2009-09-01
    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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  • 6
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    Shallow Seismic Velocity Structure of the Betic Cordillera (Southern Spain) from Modelling of Rayleigh Wave Dispersion (2005)
    Springer
    Details
    Publication Date: 2005-07-01
    Print ISSN: 0169-3298
    Electronic ISSN: 1573-0956
    Topics: Geosciences , Physics
    Published by Springer
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  • 7
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    S-wave velocity images of the Dead Sea Basin provided by ambient seismic noise (2013)
    In:  Journal of Asian Earth Sciences
    Details
    Publication Date: 2020-02-12
    Description: Based on passive seismic interferometry applied to ambient seismic noise recordings between station pairs belonging to a small-scale array, we have obtained shear wave velocity images of the uppermost materials that make up the Dead Sea Basin. We extracted empirical Green’s functions from cross-correlations of long-term recordings of continuous data, and measured inter-station Rayleigh wave group velocities from the daily correlation functions for positive and negative correlation time lags in the 0.1–0.5 Hz bandwidth. A tomographic inversion of the travel times estimated for each frequency is performed, allowing the laterally varying 3-D surface wave velocity structure below the array to be retrieved. Subsequently, the velocity-frequency curves are inverted to obtain S-wave velocity images of the study area as horizontal depth sections and longitude- and latitude-depth sections. The results, which are consistent with other previous ones, provide clear images of the local seismic velocity structure of the basin. Low shear velocities are dominant at shallow depths above 3.5 km, but even so a spit of land with a depth that does not exceed 4 km is identified as a salt diapir separating the low velocities associated with sedimentary infill on both sides of the Lisan Peninsula. The lack of low speeds at the sampling depth of 11.5 km implies that there are no sediments and therefore that the basement is near 10–11 km depth, but gradually decreasing from south to north. The results also highlight the bowl-shaped basin with poorly consolidated sedimentary materials accumulated in the central part of the basin. The structure of the western margin of the basin evidences a certain asymmetry both whether it is compared to the eastern margin and it is observed in north–south direction. Infill materials down to ∼8 km depth are observed in the hollow of the basin, unlike what happens in the north and south where they are spread beyond the western Dead Sea shore.
    Keywords: 550 - Earth sciences
    Language: English
    Type: info:eu-repo/semantics/article
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