Tsunami is a series of web caused by the earthquake at or near the ocean or sea. It is not the tidal web. It is the Japanese word called tide or web of the sea. It can generate when a sudden earthquake occur then this earthquake make the sea floor disturbance and the above huge sea water is disturbed then a web generates and start to expand all around.
The sign of Tsunami approaching!
It usually shows a retreat of seawater and makes a sea beach naked. The fishes can be seen. It indicates a huge file of water is coming.