Mapping the Thickness of Gyttja by Using the Pull-down Effect on Shallow Reflection Seismic Data

A reflection seismic survey has been carried out in Vejle fjord in Denmark in order to map the thickness of organic rich gyttja sediments. The reflection seismic data was severely contaminated by multiples and suffered from high absorption in the near surface sediments. Consequently, a direct and reliable interpretation of gyttja in the entire survey area could not be accomplished. Alternatively, the interpretation has been based on the pull-down effect on reflections which in the present case is the only way to achieve a coherent estimate on sediment thicknesses. Borehole information has been used to estimate the velocity in the gyttja layer.