Identification and Isolation of Multiple Modes in Rayleigh Waves Testing Methods

The spectral-analyses-of-surface-waves (SASW), developed in the early eighties, has constituted an important step in the use of surface waves for definition of shear wave velocity profiles without intrusion. The SASW testing procedure was designed to minimize the contribution of higher Rayleigh modes and thus assumes that the average dispersion curve is representative of the fundamental Rayleigh mode. A number of numerical studies have however demonstrated that this basic assumption is valid only when the shear wave velocity varies regularly with depth. This study demonstrates, based in numerical simulations and an experimental case, that the multi-Rayleigh mode problem can occur in various situations even if the shear wave velocity increases regularly with depth. Techniques are proposed in order to identify and separate the energy of higher modes. The applicability of those techniques is demonstrated with simulated and experimental cases.