Seismic Techniques

Continuous Surface-Wave System (CSWS)

Outline

The continuous surface-wave method utilises a specific type of seismic wave, known as the Rayleigh wave, in order to determine in situ shear modulus-depth profiles to depths of between 8m to 20m. The velocity of a Rayleigh wave is related to the shear modulus (G) and density of the ground through which it propagates. Unlike crosshole seismic methods, which are routinely used to determine geotechnical parameters such as the shear modulus (and additionally Poisson's ratio), the CSW technique require no boreholes. The system comprises a portable frequency-controlled vibrator and an array of low frequency geophones arranged co-linearly with the source. Rayleigh waves are generated at frequencies of between 5Hz and 100Hz in 0.1-5Hz increments in order to build up a comprehensive stiffness-depth profile.