On March 14, 1979 a sizeable earthquake (Ms = 7.6, Richter scale) occurred on the continental shelf adjacent to S.W. Mexico, near Petatlan in the state of Guerrero. This earthquake generated a small tsunami that was recorded in deep water, 1000 km away, thus providing for the first time a glance at a tsunami traveling in the open ocean. The same sea floor pressure record displays conspicuous signals associated with vertical sea floor motions generated at the passage of the first Rayleigh seismic wave, R1. Seismic and tsunami travel velocities are in agreement with our present understanding of the phenomena, and tsunami detectability in deep water is demonstrated to be well within present day state of the art in the design of sea floor pressure transducers. As calculations anticipate, the E.M. signals associated with the passage of the tsunami were too faint to be detected.