If there is an earthquake under an ocean, tsunami is possible.
an earthquake under the ocean caused the tsunami
tsunami
it is possible if the plates move and one of them slips under the other your tsunami will form.
tsunami
tsunami
Tsunamis occur after an earthquake. Earthquakes that occur in the middle of the ocean can force a tsunami to make landfall.
it creates a tsunami
It can trigger a tsunami.
Tsunami
tsunami
If its a large earthquake, you can expect a tsunami to follow