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    P- and SV-velocity structure of the South Portuguese Zone fold-and-thrust belt, SW Iberia, from traveltime tomography

    Access Status
    Open access via publisher
    Authors
    Schmelzbach, C.
    Zelt, C.
    Juhlin, Christopher
    Carbonell, R.
    Date
    2008
    Type
    Journal Article
    
    Metadata
    Show full item record
    Citation
    Schmelzbach, C. and Zelt, C. and Juhlin, C. and Carbonell, R. 2008. P- and SV-velocity structure of the South Portuguese Zone fold-and-thrust belt, SW Iberia, from traveltime tomography. Geophysical Journal International. 175 (2): pp. 689-712.
    Source Title
    Geophysical Journal International
    DOI
    10.1111/j.1365-246X.2008.03937.x
    ISSN
    0956-540X
    School
    Department of Exploration Geophysics
    URI
    http://hdl.handle.net/20.500.11937/23719
    Collection
    • Curtin Research Publications
    Abstract

    Imaging the architecture of the shallow crust of the South Portuguese Zone fold-and-thrust belt is essential to extend surface mapped geological information to depth and to help in developing models of the ore-bearing Iberian Pyrite Belt part of the Variscan orogeny. The recently acquired IBERSEIS seismic-reflection data set provides, for the first time, detailed images of the entire crust, but source-generated noise masks the earliest reflections and limits the shallowest observed signals to depths >500 m. We inverted P- and SV first-arrival traveltimes for the smoothest minimum-structure velocity models, imaging the shallowest few hundreds of metres along four in total ~60-km-long profiles. A comparison of a 2-D and 2.5-D (3-D forward and 2-D inverse problem) crooked-line inversion scheme revealed that the crooked-line geometry has a negligible effect on the final images. Resolution of the final preferred models was assessed on the basis of an extensive series of checkerboard tests, showing a slightly lower resolution capability of the SV-data due to greater data uncertainty, fewer number of picks and more limited source-receiver offsets compared with the P-data. The preferred final models compare favourably with the mapped surface geology, showing relatively high and uniform velocities (>5.25 km s-1) for the flysch group in the southern part of the investigation area. Low velocities (~4.5 km s-1) are found for the 'La Puebla de Guzman antiform' in the centre of the investigation area, where the phyllite-quartzite group is exposed. Velocities fluctuate the most along the northernmost ~20 km. Velocity variations reflect more the state of tectonic deformation than being directly correlated with the mapped lithologies. Based on a comparison with coincident seismic-reflection data along the southern half of the area, we suggest that two areas of low to intermediate ratios (~1.85-1.9) correspond to occurrences of thick and less deformed flysch-group units, whereas high VP/VSV ratios (~1.95) are interpreted to indicate increased porosity due to intense fracturing. © 2008 The Authors Journal compilation © 2008 RAS.

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