Approximate approach to analyzing effective velocity of surface waves

The Rayleigh waves on layered systems are of multimode. The transient responses of the surface are comprised of ones of multimodes. In the near field where propagating distance is small relative to the wavelength, the propagating velocities of modal responses vary with the distance from the loading center, and approach to the phase velocities of modes in the far field. Affected by higher Rayleigh wave modes in the surface wave field, the effective phase velocity obtained by spectral analysis of surface waves (SASW) is not corresponding to the phase velocity of the fundamental mode. The effective phase velocity varies with the propagating distance. In the near field, the body waves have great influences on the effective phase velocity. The theoretical effective phase velocities can be got by spectral analysis of the discrete solution of surface displacement; the layer parameters can be evaluated by matching the measured phase velocity data with the theoretical ones. Influences of the near field as well as higher modes on the effective phase velocity are taken into consideration in this method.