Strong ocean bottom earthquakes occur every day in different parts of the planet. They result in the appearance near coast of gigantic devastating tsunami waves, while in the region of the earthquake epicenter unusual hydrodynamic phenomena are observed. Even at the time of great geographical discoveries the Spanish and Portuguese seafarers described such phenomena as "sea shaking" or "awful sea". Now the term "seaquake" is widely used. The transverse dimension of the perturbated region of the sea surface during a seaquake usually exceeds 10–100 km, while the duration of a strong seaquake may amount to 10 min. During a seaquake sets of very steep standing waves form on the surface of the aquatorium, there arise individual vertical columns of water, solitary water formations arise, and strong acoustic effects are noted. Spray sultans may be observed, as well as cavitational layers of water separating from each other and flying apart. Water colour and water temperature can change. Wave height can exceed 10 m, and the surface movement speed can reach 10 m/s. A ship that happens to be in the zone of influence of a seaquake turns out to be surrounded by giant standing waves filling up the entire visible space. Terrible thunderous rumbling and howling are enhanced by sharp blows to the bottom, the most strong shaking of the vessel and the destruction of deck structures that had in the past endured more than a few storms.
Seaquake database contains actual information about seaquakes. Information from tsunami catalogs, records of logbooks, scientific publications and mass media are verified with USGS earthquake catalog. For each seaquake following information is provided: time and the place when and where this event was observed, parameters of an earthquake which caused this event, descriptions how the event was felt by eyewitnesses.