Elastic wave and excitation mechanism of surface waves in multilayered media

Abstract

The elastic wave field and the excitation mechanism of the surface waves in multilayered elastic solid media are studied in this paper. On the basis of Abo-zena [Geophys. J. R. Astron. Soc. 58, 91–105 (1979)] and Menke [Geophys. J. R. Astron. Soc. 59, 315–323 (1979)], the elastic wave field is further investigated in the B, P, C coordinate system. The so-called new type of propagator matrix introduced by Menke to avoid loss of the precision problem is improved. It presented an important result and some new properties. The dispersion characteristics and excitation mechanisms of the surface waves (Rayleigh and Love waves) are also investigated via numerical simulation. The excitation intensities of the surface waves strongly depend on the frequency range of the source. The source frequency should be controlled in a proper range to effectively excite the surface waves. Two quantities, β1 (the ratio of B to P components of displacement) and β2 (the ratio of B to P components of stress), are defined for the Rayleigh wave. It is found that β1 and β2 are sensitive to the material property of the medium and the layered geometry, and they are two important physical 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 β1 and β2 is less than 10%. The effects of the thickness of each layer of media and other factors on the dispersion characteristics of Rayleigh and Love waves and the values of β1 and β2 are also analyzed.

Characterization of the sedimentary cover at the Himalayan foothills using active and passive seismic techniques

“…These methods are based on the dispersion property of the surface waves, which is the most sensitive property to S-wave variations with depth (Zhang et al, 1996). As the wavefield generated by active or passive seismic sources (e.g.…”

Propagation characteristic of laser-generated visco-elastic Rayleigh-like waves in stratified half-space

“…The SAW velocity starts at the Rayleigh velocity of the bottom substrate (aluminum) and slopes downward to the Rayleigh velocity of the adhesive layer (epoxy); meanwhile, the attenuation goes through a precipitous rise, then the SAW velocity begins to increase before it reaches the velocity of the adhesive layer yet, which means the more energy go into upper medium (the elastic medium aluminum). But, the SAW velocity reduces abruptly approaching the shear velocity of the middle layer before it reaches the velocity of the upper substrate (about 20 MHz), which are called "energy trap" [9], which indicates that there is energy leaking into adhesive layer again, viz. the waves are "leaky waves" which should also be considered pseudo-Rayleigh waves.…”

“…Zininet et al [5] pointed out that a pseudo-Rayleigh wave leaks energy into substrate. Lawr ultrasonics have been widely used to study the SAWs of multilayered adhesive structures [6][7][8][9], and its advantages include providing a non-contact, wide band, perfect source. Cheng et al [10] have simulated laser-generated ultrasonic waves in a layered plate.…”

Statistical properties of the seismic noise field: influence of soil heterogeneities

“…Since ambient seismic noise is mainly composed of surface waves, and therefore contains vital information about the velocity structure, this allows dispersion curves to be obtained from array noise recordings (Zhang et al 1996) based on phase-coherency measurements between all pairs of signals between the stations. To this regard, four micro-array measurements have been carried out in the urban area ( Fig.…”