ELASTIC-WAVE AND EXCITATION MECHANISM OF SURFACE-WAVES IN MULTILAYERED MEDIA

The elastic wave field and the excitation mechanism of the surface wav es in multilayered elastic solid media are studied in this paper. On t he basis of Abo-zena [Geophys. J. R. Astron. Sec. 58, 91-105 (1979)] a nd Menke [Geophys. J. R. Astron. Sec. 59, 315-323 (1979)], the elastic wave held is further investigated in the B, P, C coordinate system. T he so-called new type of propagator matrix introduced by Menke to avoi d loss of the precision problem is improved. It presented an important result and some new properties. The dispersion characteristics and ex citation mechanisms of the surface waves (Rayleigh and Love waves) are also investigated via numerical simulation. The excitation intensitie s of the surface waves strongly depend on the frequency range of the s ource. The source frequency should be controlled in a proper range to effectively excite the surface waves. Two quantities, beta(1) (the rat io of B to P components of displacement) and beta(2) (the ratio of B t o P components of stress), are defined for the Rayleigh wave. It is fo und that beta(1) and beta(2) are sensitive to the material property of the medium and the layered geometry, and they are two important physi cal quantities for exploring the structures of the interfaces and the velocity distributions of layers under the free surface. The relative error in estimating the thickness of each medium by beta(1) and beta(2 ) is less than 10%. The effects of the thickness of each layer of medi a and other factors on the dispersion characteristics of Rayleigh and Love waves and the values of beta(1) and beta(2) are also analyzed. (C ) 1996 Acoustical Society of America.