Amplitudenaenderung tiefer Reflexionen Abschlussbericht

The propagation of seismic waves in inhomogenious media is influenced mainly by the reflection/transmission process at seismic boundaries and by attenuation inside the layers. Small scale (in relation to the profile length) variations of mean seismic amplitude level are frequently observed in onshore exploration for oil. Detailed investigations relating the cause of diminishing are unknown. Starting with the hypothesis that the described effect relates to near surface inhomogeneities a new technique was developed. It provides information for the interpretation of amplitudes and frequencies of deep seismic soundings. As for the changed amplitude level, some 'dynamic' parameter have been calculated from the spectra of the data and put into a surface chart. Colour coding leads to special arrangements of rows and columns. A crossing of equal coloured rows and columns at zero offset position in the surface chart means that there is a good agreement between the subsurface conditions of shots and receiver at the same profile position, respectively. Searching for crosses means searching for positions on the profile where the transmission conditions are disturbed in relation to geophones and source points. Applications of this new technique have been performed successfully with model data and with parameters life f_m_a_x, bandwidth, mean amplitude and energy. A careful and thorough analysis of vibrator reflection data shows that there has been an unknown normalization before correlation. Therefore this data has been excluded from further amplitude investigations. The method developed is a contribution to the interpretation of deep seismic reflection data. Its potential consists in a compressed representation of information from the subsurface. That can be used to correct for amplitude changes which otherwise are interpreted as crustal effects. (orig.)Available from TIB Hannover: F97B1455+a / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEBundesministerium fuer Bildung, Wissenschaft, Forschung und Technologie, Bonn (Germany)DEGerman