When you throw a stone or rock into water, you will notice that it creates ripples. When the rock hits the water, it moves downwards a lots of energy, and some of this energy moves outwards from the center. At the same time, the surface of water is pushed down a bit, but since the surface of the water has elastic quality, it comes back and moves outwards, creating the ripples that we see.
These ripples are always in a circular pattern, whatever the shape of stone or rock may be. These ripples will continue as long as the center continues to ‘bounce’. When the water’s equilibrium is restored , the surface is still again, until the next rock, stone or pebble is thrown.