A method is provided to distinguish two blended but different waves in a structure, such as compressional and shear waves, by measuring their corresponding wavenumbers and wave speeds. Other characteristics of the two waves may also be measured such as the propagation coefficients of both waves. All measurements can be calculated at every frequency for which a transfer function measurement is made. The measurements do not depend on the resonance frequencies of the structure and do not require curve fitting to the transfer functions.