Direct and continuous measurement of depth-dependent reflection coefficients of Rayleigh waves for surface discontinuity: Normal slot

Abstract

A new method and principle were presented for the continuous measurement of the depth-dependent reflection coefficient of Rayleigh waves or their pulse interacting with various surface discontinuities. The method was to record the reflection echo amplitudes for varying depth during scanning the Rayleigh wave pulse with a small lateral beam width along a surface discontinuity with a small slope in depth. In the experiments using a declined slot and intensively focused Rayleigh waves, the coefficients were continuously measured with quite good reproducibility in the range of 0.05<d/λ (slot-depth/Rayleigh wave wavelength) <2.57. In 0.05<d/λ<1.4, the results showed good agreement with other experimental results that had been determined by conventional method [L. J. Bond, Ultrasonics 71, 71–77 (1979); M. Hirao et al., J. Acoust. Soc. Am. 72, 602–606 (1982); H. M. Frost et al., Proc. Ultrason. Symp. IEEE (1975), 604–607] as intermittent point-to-point data and several numerical results [L. J. Bond, Ultrasonics 71, 71–77 (1979); R. J. Blake and L. J. Bond, ibid. 28, 214–228 (1990); M. Munasinhe, Ph.D. thesis, McGill University, Canada 1973; A. K. Mal and L. Knopoff, Bull. Seismol. Soc. Am. 55, 319–334 (1965)]. Especially, in the extremely shallow range of 0.05<d/λ<0.3, the reflection coefficients, showing quite good agreement with the numerical estimation, were measured while any other experimental data for slots or down steps have not been reported in 0.05<d/λ<0.25. It was shown that the new method could be used to evaluate more conveniently and quantitatively the depth or depth profile of various surface features in the long-wavelength or shallow-depth region of about 0.05<d/λ<0.5.