Deep crustal seismic reflection profiles across the Little Carpathians and adjacent margins of Vienna Basin and West Danube Basin in Czechoslovakia

Blais, Estelle (1992) Deep crustal seismic reflection profiles across the Little Carpathians and adjacent margins of Vienna Basin and West Danube Basin in Czechoslovakia. Masters thesis, Memorial University of Newfoundland.

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Abstract

Within the accretionary wedge forming the Carpathians of Central Europe, several 'basement' horsts occur within the usual sequence of thrust wedges, or nappes. This thesis is concerned with one such anomaly - the Little Carpathian horst in the Western Carpathians in Czechoslovakia. The horst is located between two deep post-nappe basins: the Vienna and West Danube basins, so that the structural relations with the underlying nappe sequences is unclear from surface geology. -- The main objective of this study is to define the structure of the Little Carpathian portion of the accretionary prism and the basin margins. To address this tectonic problem, three seismic reflection lines from Geofyzika Brno were reprocessed. The objective of the reprocessing was to improve the signal-to-noise ratio and velocity analysis to enhance reflectors buried in cultural noise (12.5 Hz and 16.7 Hz) in many places. Deconvolution, bandpass filtering, frequency filtering and velocity analysis were the main steps of reprocessing. Only common-mid-point (CMP) gathers without binning information were available, thereby limiting re-processing to post gather processes. Reprocessing greatly attenuated diffractions at the margins of the Vienna basin and West Danube basin and improved signal-to-noise ratio in some zones of the seismic sections. The main objectives of reprocessing were met though the extent of improvement is modest. -- The interpretation of the reprocessed seismic sections yielded interesting results. Late Cretaceous thrust related structures within the Little Carpathian horst were identified, such as the base of the Bratislava massif, thrust onto the Modra massif. A trailing imbricate fan structure within the Envelope nappe was also imaged. Reflections at the margin of the Vienna basin and West Danube basin were correlated with borehole data, and their dips are in agreement with no or very little thermal subsidence in the Vienna basin as the reflections are close to horizontal and faulting is intensive.

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