Abstract:

Based on the thin layer stiffness matrix method, the behavior of Rayleigh waves in three typical media with smoothly varying stiffness is studied and compared with that in the layered media. The results show that whether the stiffness profiles are smoothly varying or layered, the fundamental mode dominates the surface wave field and the effective phase velocity approaches to the phase velocity of the mode in far field for the regular profiles. For the irregular profiles, the higher modes have a significant influence on the surface wave field. The intensity and the frequency range of the influence are related to variation of the profile stiffness. In media with smoothly varying stiffness, the tendency of the effective phase velocity of mode at high frequencies is above Rayleigh wave velocity of the medium with the smallest shear velocity; and the tendency of the phase velocity at high frequencies deviates from Rayleigh wave velocity of the surface medium. These characteristics are different between the layered media and the media with smoothly varying stiffness. The results show that when a medium with smoothly varying stiffnesses is modelled with a layered medium in the back-analysis of the measured dispersion data, the match between the measured and the theortical dispersion data and the calculated stiffness profile are influenced by number of layers.

Key words: thin layer method, Rayleigh waves, mode, effective phase velocity, medium with smoothly varying stiffness, layered medium