Book excerpt: The information and technology necessary to derive a valid geological-geophysical-acoustic model of the sea floor are presented. Two contrasting models are detailed and discussed: one in the Bering Sea which has a shallow-water, high-velocity, hard-sand bottom; and the Mohole (Guadalupe Site) model which has a deep-water, low-velocity, soft-clay bottom. Other models are to be reported in a continuing series. (Author).