This study investigates how a system of incident harmonic waves affects the interface motion between two materials. To that end diffraction of a system of cylindrical harmonic SH waves by a random interface between two elastic half-spaces is investigated using a direct boundary integral equation approach. In particular, the incident system consists of a primary source of unit amplitude and an arbitrary number of secondary sources placed along an ellipse centered at the primary source. The interface peak amplitude, the number of the secondary sources, and the frequency are assumed to be arbitrary.
Response along the random interface is computed for different frequencies and the source configurations. The interface motion is found to strongly depend upon the incident system. Two incident system configurations are identified that produce the interface motion that is considerably amplified or reduced when compared to the corresponding displacements due to a single unit primary source. The two systems share the same geometry and the source amplitudes but have different source amplitude phases.