Deltares regularly conducts marine seismic surveys. A recent development involves using Scholte waves to measure the stiffness of the seabed, an important parameter in many offshore and nearshore projects such as the construction of wind farms, trenching and dredging work.
Extension of MASW
Together with the Delft University of Technology, Deltares has developed a measurement technique for mapping out this parameter and, above all, spatial variations in it. The shear wave velocity and the stiffness of the subsurface are linked. On land, shear wave velocity can be measured using MASW (Multichannel Analysis of Surface Waves). This technique is used worldwide. We have developed it further for the application at sea. The technique uses specific shear waves known as Scholte waves, which move in the upper part of the seabed,covering a range of tens of meters.
Numerous adjustments were required to enable the use of this proven technique for marine applications. The technical adjustments are related to the source of the vibration and the configuration of the sensors. During the analysis of the data, we have to take the water layer between the source, the sensors and the seabed into account. In the Scholte Waves study, we determined the optimal configuration for mapping out the stiffness of the bed at sea or in other surface waters, developed software for the analysis of the measurements, and conducted several tests at sea.