WAVES IN ELASTIC AND ANELASTIC STRATIFIED MICROSTRUCTURE - A NUMERICAL COMPARISON

Burridge et al. [J. Acoust. Sec. Am. 94, 2884-2894 (1993)] presented a fast algorithm to compute wave propagation through a stack of finely layered elastic or anelastic microstructure. The method goes beyond pr evious work in two aspects: (a) the sample autocorrelation is used so that the coda of the computed response is preserved; and (b) the anela stic effect due to intrinsic attenuation is incorporated and by order- of-magnitude argument, the terms governing the scattering and anelasti c effects enter separately but in a similar way. The present work is a numerical justification of the perturbation theory. Using a standard linear solid model with a single Debye relaxation mechanism, a finely layered microstructure was made anelastic. Using the SH case as an exa mple, impulse responses were computed using two methods: the approxima te method and an exact method for both elastic and anelastic media at normal and oblique angles of incidence. The impulse responses obtained by the two methods agree well for both elastic and anelastic cases. T he results of the investigation can be summarized in several points: ( a) accuracy is best for the head of the pulse; (b) the presence of ane lasticity increases the time delay and dispersion of the broad pulse; and (c) the perturbation code is 30-54 times faster than the exact cod e. (C) 1998 Acoustical Society of America.