Model studies on the effect of a sloping interface on Rayleigh waves

Abstract

Seismic models were studied to determine the effect of a sloping interface on the propagation of Rayleigh waves. The two-dimensional model, 1/16 inch thick, consisted of a plexiglass surface layer and a panelyte half-space. The surface layer ranged from ¼ to ¾ inch in width with a dip of approximately 2½°. When the variation in layer thickness is linear and gradual, a region of sloping interface (or a wedge-shaped structure sufficiently remote from its vertex) may be represented to a good approximation by an infinite number of stepped flat layers. The phase velocity of Rayleigh waves determined from a pair of adjacent stations in the region of sloping interface is an ‘effective phase velocity.’ As the distance between the stations approaches zero, the effective phase velocity approaches a limiting value defined as local phase velocity/which is independent of the direction of wave propagation. Outside the region of sloping interface and away from the points of discontinuous slope change, the Rayleigh wave velocities are those appropriate for the flat layer thicknesses; they seem to be unaffected by the nearby sloping interface. As an example, the phase velocities of Rayleigh waves for a generalized crust-mantle structure with a sloping interface are given.