A note on plane-wave approximation

• Effects of fault proximity on the plane SH wave approximation are studied.
• Amplification of incident cylindrical and plane SH waves in semi-cylindrical valley.
• Calculations are formulated via imaging method relative to the free surface.
• Plane wave approximation is suitable for many site amplification studies.

It is shown that the plane-wave assumption for incident SH waves is a good approximation for cylindrical waves radiated from a finite source even when it is as close as twice the size of inhomogeneity. It is concluded that for out-of-plane SH waves the plane-wave approximation should be adequate for many earthquake engineering studies.