Modeling shear and compressional head waves at velocity steps and inversions

Abstract

Accurate modeling of head waves (lateral waves or refractions) enables improved estimation of sound velocities at and below the ocean bottom, [A.D. McAulay, in Int. Conf. Acoustics Speech and Sig. Proc. 1980, 1981]. Head waves arise when a homogeneous wave strikes an interface with a medium of greater velocity (step) at greater than the critical angle or, less well known, when an inhomogeneous wave strikes an interface with a medium of lower velocity (inversion). In practice head waves are caused by an inhomogeneous wave either when a point source is located near a velocity inversion, or at the exit of a tunnel through a high velocity region. A computer program was developed using the Thompson-Haskel formulation and the Delta matrix method to obtain fast accurate modeling of shear and compressional waves for a plane layered model and a point source. Various velocity models were used to illustrate the accurate modeling of shear and compressional head waves. In particular the accurate modeling of head waves at a velocity inversion is illustrated for the first time.