The appearance of the pP phase, on seismograms, is strongly affected by the crustal structure in the vicinity of the epicenter. A recognizable pP phase is generated near the west coast of North America when the uppermost layer is water of sufficient depth. The generation of this pP is also affected by ocean bottom conditions. The bottom must probably be flat and the coefficient of reflection between the water and the bottom must be high. This pP phase may be useful in epicenter location and in crustal studies.