in the deep ocean, where the depth is typically 4000 m, the speed of long waves increases to approximately 200 m/s. the difference in speed, when compared to the shelf, is responsible for reflections at the continental shelf edge. away from resonance this can reduce tidal energy moving onto the shelf. however near a resonant frequency the phase relationship, between the waves on the shelf and in the deep ocean, can have the effect of drawing energy onto the shelf.