Figure 18 is an example of a single common shot gather from a marine seismic survey. The traces from the receivers closest to the source are in the center of the gather and those traces from the receivers farthest away are at either side of the gather. A seismic survey will consist of a few thousand of these gathers for smaller 2D surveys to several million for a large 3D survey.
Several different types of signal can be observed in this example. Arrivals coming directly from the source without being reflected can be seen at A. The reflection from the water bottom is labeled B. M1 is the water bottom multiple as shown in the earlier diagram. Since it has only a single extra path from the surface to the water bottom and back it is know as a first order multiple. M2 is also a first order multiple, but from shallow surface beneath the sea bottom. It is similar to the water bottom multiple P is a primary reflection and PL is a peg leg multiple coming from it.
Figure 18 Common shot gather from a marine survey (Yilmaz, 1987)