Effects of Multiple Modes on Rayleigh Wave Dispersion Characteristics

Abstract

The effects of multiple modes on Rayleigh wave dispersion are discussed to reduce the ambiguity of uniqueness of shear wave velocity (Vs) profiles estimated by the surface wave method. Based on a review of previous studies, dispersion curves of multiple‐mode Rayleigh waves induced by harmonic vertical point loading are derived for both vertical and horizontal particle motions. Also presented is the variation with frequency of the amplitude ratio between horizontal and vertical particle motions. Numerical studies indicate that a stiff soil layer overlying a softer soil layer induces a higher mode or multiple modes, leading to an inversely dispersive characteristic. Consideration of the effects of higher modes is strongly recommended in the inverse process when the observed data show an inversely dispersive trend. The ambiguity of uniqueness of the inverted soil profiles may be reduced by using either the dispersion data of horizontal motion or the amplitude ratio of particle motions in addition to the disp...