In Japanese: tsu=harbor nami=wave
Caused by earthquakes, landslides, cosmic collisions (meteorite impact)
Very long wave length 100 - 200 km !
In depths of 1-4 km they propagate as shallow water waves! ( 
)
Very high speed! for d=4,000 m
= 198 m/s = 713 km/h
Very large periods! 
= 505 sec = 8.41 min
For more information:
(a) SPM, pp. 3-92 to 3-94
(b) http://www.geophys.washington.edu/tsunami
(good web site with simulations, photos and records of major tsunamis)