Kenji Satake and colleagues at the Japanese Geological Survey have simulated a tsunami generated by a large subduction-zone earthquake in the Juan de Fuca area. The map above shows what the waves might have looked like 4 hours after the event. Of course the vertical exaggeration is extreme. In the open ocean tsunami waves are rarely more than a metre or two high, and are not noticeable to passing ships because of their very long wavelengths (ca. 100 km).
from: Satake, K. et al., 1996, Time and size of a giant earthquake in Cascadia inferred from Japanese tsunami records of January 1700, Nature, V. 379, p. 246-249.