Scattering of elastic waves by an alluvial valley of arbitrary shape is investigated. The valley, embedded into linearly elastic, homogeneous, and isotropic half-space, is subjected to incident plane harmonic wave. Surface displacement field is evaluated numerically for semi-elliptical alluvial valley and incident SH, P, SV, and Rayleigh waves for different depths of the alluvial valley. The results indicate that the interface depth might influence differently the surface displacement field for different incident waves and at different frequencies. At low frequency (Ω = 0.4) and fixed angle of incidence (θo = 30°), the surface displacement field due to SH waves is less sensitive to the increase in the interface depth compared to surface motion due to P and SV waves. At higher frequency (Ω = 1), the surface motion is very sensitive upon the change in depth of the interface.