# How much time is there between an underwater earthquake and the moment a tsunami hits the coast?

Tsunamis can be caused by underwater earthquakes, like the 2004 tsunami in the Indian Ocean. The precise value will likely depend on where the earthquake is relative to the coast. But what is the time range between the moment the earthquake is detected and the moment a tsunami hits the coast? Is it minutes? Hours?

• There are so many variables which would be in play here. Seismograph data availability, where the epicentre is (magnitude, depth, distance from coasts), how capable are the locations able to be contacted.... – Chris Rogers Sep 14 '20 at 15:27
• I don't see how whether the locations are able to be contacted comes into play. I'm not asking how long it would take for someone with a sismograph to warn someone on the coast. Just how long between the initial earthquake and the subsequent tsunami. – usernumber Sep 14 '20 at 16:13
• @usernumber you can take a look here en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami for information about the speed and timing of the tsunami. – trond hansen Sep 14 '20 at 17:49
• The question sounds pretty clear to me, vote to leave open. – Jean-Marie Prival Sep 15 '20 at 6:42

• A tsunami is a shallow wave, meaning the wave reaches all the way to the bottom of the ocean, even at its deepest. Shallow waves propagate with a speed of about $\sqrt{gd}$ where $g$ is the acceleration due to gravity and $d$ is the depth. – David Hammen Sep 15 '20 at 17:34