In this work, plausible ocean bottom structures have been represented by stacks of homogeneous, isotropic, nonabsorbing, plane horizontal layers. Generalized ray theory was used to calculate the seismic responses of these bottom models in a frequency band of 1--30 Hz for a receiver near the ocean's surface and located 2--20 km away from a sound source also near the ocean's surface. The model's responses depend most strongly upon the velocity structure of the basement rock and on the presence or absence of a zone of partial lithification between unconsolidated sediments and basement. The thickness and velocity gradients in the unconsolidated sediments have a smaller effect on the models' seismic responses. Joint consideration of both basement head wave and reflection amplitudes constrains basement velocity structure much more than separate consideration of either phase, thus emphasizing the importance of accurate recording and careful analysis of bottom reflections as well as refracted arrivals in marine refraction profiles.