Seismic profiling of the seabottoms for shallow geological and geotechnical investigations

Abstract

This chapter presents the seismic profiling of the seabottoms for shallow geological and geotechnical investigations. Both methodology and equipment needed to perform the deep and shallow seismic surveys shall be discussed as well as the presentation of the results on the example of the Polish Baltic Sea. Of utmost importance, in identifying the geological structure of the Quaternary substrate deposits occurring on the seabed, is the seismoacoustic research. In this study the interpretation of the results is based on the analysis of different reflective levels, the nature of the borderlines of reflective horizons, their relative clarity and angles. Then, the correlation is made between seismoacoustic materials and geology of the adjacent land area. This correlation is based on the use of geological maps and drilling cores from the coastal zone, taking into account the lithology, stratigraphy and depth of occurrence of certain reflective levels and the surface of angular discordance. This allows an initial presentation of the bedrock structure and establishing the correlation between sub-Quaternary surface and lithological composition of deposits. The conducted seismoacoustic investigations within the Quaternary sediments provides a basis for separation of certain seismostratigraphic units, which refer strictly to the separate litostratigraphic levels of the analyzed geological period. An important aspect of the interpretation of seismic records is to analyze the degree of the acoustic energy absorption through the different layers of Quaternary sediments along with characterization of the records’ texture. An important element in the analysis of seismoacoustic registrations is also the tracking of the leading acoustic horizons and the analysis of angular discordance of individual reflectors. The role of seismoacoustic investigations in the geotechnical recognition of the seabottom is also very important because, conducted on a large-area and with a set accuracy, these tests can determine the limits of occurrence of particular soils that have specific physical and mechanical properties. An important aspect of seismoacoustic investigations in the geotechnical recognition of the seabed is also to specify the thickness of geological layers that can become the selected substrate for the foundation of certain buildings and marine constructions.