Dickmann, Thomas (1993) Das Konzept der Polarisationsmethode und seine Anwendungen auf das seismische Vektorwellenfeld im Weitwinkelbereich. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, 127 pp. . GEOMAR-Report, 019 . DOI 10.3289/GEOMAR_REP_19_1993.

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Abstract

Based on the vector character the treatment of the three-dimensional seismic wavefield
becomes complex. With the exploitation of converted wave-modes the acquisition of vectorwavefield
data is effective, especially in the wide-angle range. Consequently shear waveacquisition
with conventional sources, including marine sources, is possible and only multicomponent
seismometers are required.
Using this method wide-angle recordings of high quality were obtained within the
BABEL-project (Baltic and Bothnian Echoes from the Lithosphere). However the processing
of such vector-wavefield data raises the question of how to decompose the wavefield in its
single modes.
This thesis classifies the separation techniques, which have been presented in the literature,
and shows a strong connection between polarization and separation of the seismic wavefield.
Taking wide-angle data into particular consideration a discussion of these methods
demonstrates the general applicability provided that equidistant traces are available.
It is found out with the Controlled Orientation - a further developed method for the
automatic reorientation of three-component recordings - that the alignment of refraction
seismic data to the direction of the P-wave first arrival is not reliable because of the nearly
vertical incidence. However it turns out, that the correction of the apparent angle of incidence
need not be considered.
With the processive realization of equidistant traces it is demonstrated that the amplitude
character for the analysis of polarization is preserved. Therefore a multi-trace procedure can
be implemented, which is in a position to process effectively long offset three-component
data based on a two-dimensional operator window. This two-dimensional polarization-filter
works data-adaptively for the determination of polarization parameters and is superior to the
conventional method of Montalbetti and Kanasewich (1970). Three-component wide-angle
data are used to illustrate the improvements obtained in noise reduction and in wave-mode
separation using this technique .

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