<p>As a general guideline, the time between the actual earthquake and the time the tsunami arrives is on the order of minutes to hours.</p>
<p>Tsunamis out in the deep ocean travel very fast -- around 500 mph -- which means that they cross ocean basins in about as much time as it takes a plane to fly across. So an earthquake in Japan gives Hawaii and the US West Coast many many hours of warning.</p>
<p>Close to shore, tsunamis are much slower, but of course the distances are also shorter. For a place where earthquakes happen close to shore because of a subduction zone, say in Japan, this only gives you a few or a few tens or minutes of advance warning. If you take the 2011 tsunami in Japan, warnings were sounded quite quickly, and that allowed a large number of people to get to higher ground and will have saved tens of thousands of lives. But at the same time, it was not enough time to actually go door to door, put people onto buses, and get them out of harm's way if either they did not hear the warning, or refused for whatever reason to immediately evacuate.</p>

CC BY-SA 4.0
2020-09-15T07:21:11.477Z
(+ the seismic wave created by the earthquake propagates at, say, 2 miles per second(!); so, about 15 times faster than the tsunami. If you, furthermore, have a few seismic stations close to the earthquake you can in principle warn the rest of the world about the risk pretty much instantaneously)
Erik
CC BY-SA 4.0
2020-09-15T17:34:40.557Z
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
CC BY-SA 4.0
2020-09-18T02:57:35.467Z
Here's a link to a brief explanation on how to calculate the speed: https://www.weather.gov/jetstream/tsu_prop As noted, about 500 mph/800 km/hr in the deep ocean.
jamesqf
CC BY-SA 4.0
2020-09-15T00:35:57.473Z
2020-09-16T21:37:05.620Z
2020-09-16T21:37:05.620Z
Wolfgang Bangerth
<p>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?</p>

CC BY-SA 4.0
2020-09-14T15:27:09.210Z
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
CC BY-SA 4.0
2020-09-14T16:13:29.803Z
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
CC BY-SA 4.0
2020-09-14T17:49:50.077Z
@usernumber you can take a look here https://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami for information about the speed and timing of the tsunami.
trond hansen
CC BY-SA 4.0
2020-09-15T06:42:37.857Z
The question sounds pretty clear to me, vote to leave open.
Jean-Marie Prival
<earthquakes><tsunami>
How much time is there between an underwater earthquake and the moment a tsunami hits the coast?
usernumber
# How much time is there between an underwater earthquake and the moment a tsunami hits the coast?

(Asked by: username_0 on 2020-09-14)

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?

**Tags:** earthquakes, tsunami

> **Comments:**
> **username_1**: 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....  
> **username_0**: 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.  
> **username_2**: @username_0 you can take a look here https://en.wikipedia.org/wiki/2004_Indian_Ocean_earthquake_and_tsunami for information about the speed and timing of the tsunami.  
> **username_3**: The question sounds pretty clear to me, vote to leave open.  

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## 1 answers

### Answer by username_4 on 2020-09-15. Score: 5 | Accepted answer

As a general guideline, the time between the actual earthquake and the time the tsunami arrives is on the order of minutes to hours.

Tsunamis out in the deep ocean travel very fast -- around 500 mph -- which means that they cross ocean basins in about as much time as it takes a plane to fly across. So an earthquake in Japan gives Hawaii and the US West Coast many many hours of warning.

Close to shore, tsunamis are much slower, but of course the distances are also shorter. For a place where earthquakes happen close to shore because of a subduction zone, say in Japan, this only gives you a few or a few tens or minutes of advance warning. If you take the 2011 tsunami in Japan, warnings were sounded quite quickly, and that allowed a large number of people to get to higher ground and will have saved tens of thousands of lives. But at the same time, it was not enough time to actually go door to door, put people onto buses, and get them out of harm's way if either they did not hear the warning, or refused for whatever reason to immediately evacuate.

> **Comments:**
> **username_5**: (+ the seismic wave created by the earthquake propagates at, say, 2 miles per second(!); so, about 15 times faster than the tsunami. If you, furthermore, have a few seismic stations close to the earthquake you can in principle warn the rest of the world about the risk pretty much instantaneously)  
> **username_6**: 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.  
> **username_7**: Here's a link to a brief explanation on how to calculate the speed: https://www.weather.gov/jetstream/tsu_prop As noted, about 500 mph/800 km/hr in the deep ocean.  

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