Marine Geophysics, Geotechnical and Sonar Specialists
(+61) 0405 436 676  - allen@geosonicsaustralia.com

A Surface wave can best be described as a seismic wave that travels along an interface. In this case, the interface is the water - sediment boundary (seafloor). An analogous wave type can be seen in ocean swells. Here we can see the ocean swells change as they approach the shoreline (a change in boundary conditions). Similar to this, surface waves on the seafloor represent and change with the material below in the sub-bottom. The surface wave velocity and frequency along the seabed interface represent the character of the seafloor and sub-bottom.

Since surface waves are a "fundamental" seismic mode, they are easily identified with the use of seafloor sensors and a seismic source. The figure below shows a seismic record hi-lighting the surface wave mode:

 

 

Extracting the velocity and frequency information of the surface wave shown above is best acheived using Wavelet Transform Techniques. These techniques are similar to a standard FFT, but have the capability to "focus" on pulse type events with variable frequency. The output of this transform yields frequency and velocity information on the "shear" characteristics of the seafloor and sub-bottom - See below.
Low frequency surface wave
Using the information shown in the plot above, we can extract important geotechnical information on the seafloor and sub-bottom geology. This includes elastic moduli, bearing capacity and other parameters. Please contact us for more information.