Quantitative imaging of the Permo-Mesozoic complex and its basement by frequency domain waveform tomography of wide-aperture seismic data from the Polish Basin
Michal Malinowski and Stéphane Operto
Journal name: Geophysical Prospecting
Issue: Vol 56, No 6, November 2008 pp. 805 - 825
Special topic: Towards a Full Waveform Inversion
Info: Article, PDF ( 2.91Mb )
In this study we present the workflow and results of 2D frequency domain waveform tomography applied to the global-offset seismic data acquired in central Poland along a 50-km long profile during the GRUNDY 2003 experiment. The waveform tomography method allows full exploitation of the wide-aperture content of these data and produces in a semi-automatic way both the detailed P-wave velocity model and the structural image (i.e., perturbations in respect to the starting model). Thirteen frequencies ranging from 4 to 16 Hz were inverted sequentially, gradually introducing higher wavenumbers and more details into the velocity models. Although the data were characterised by relatively large shot spacings (1.5 km), we obtained clear images both of the Mesozoic and Permian sedimentary cover. Velocity patterns indicated facies changes within the Jurassic and Zechstein strata. A high velocity layer (ca. 5500 m/s) was found near the base of Triassic (Scythian), which made the imaging of a deeper layer difficult. Nevertheless, we were able to delineate the base of the Permian (i.e., base of the Rotliegend), which was not possible to derive from conventional common-depth-point processing, as well as some deeper events, attributed to the Carboniferous. The sub-Permian events formed a syn-form which favoured our previous interpretation of a depression filled with Upper Carboniferous molasse. The validity of the waveform tomography-derived model was confirmed by well-log data. Forward ray-tracing modelling and synthetic seismograms calculations provided another justification for the key structures present in the waveform tomography model.