The velocity of surface waves generated is directly related to ground stiffness. The speed of shorter wavelengths is influenced by the stiffness of shallower layers and the longer wavelengths by the stiffness of deeper layers, so measuring the velocity over a range of frequencies means a stiffness depth profile can be produced. GSS Advanced Continuous Surface Wave (ACSW) system is controlled and evaluated by GSS’s bespoke C-DAS data acquisition and analysis software which provides easy-to-understand outputs. Importantly, as part of the analysis process a shear wave velocity (Vs) profile is generated which can be used for seismic design or site assessment.