# Sendai quake: how long before the tsunami stuck?
**URL:** https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377
**Category:** Factual Questions
**Created:** [March 12, 2011, 4:44am UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377 "2011-03-12T04:44:14Z")
**Posts on this page:** 16
**Page:** 1
### Author:  [@squeegee](https://boards.straightdope.com/u/squeegee)
#### Post date: [March 12, 2011, 4:44am UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/1 "2011-03-12T04:44:14Z")
Apologies if this has been asked & answered already:
How much time elapsed between the Sendai quake and when the tsunami struck the east coast of Japan? I’ve seen reports of 10-15 minutes – are these accurate? I’m trying to piece this together from news reports and wikis and such, and failing. There’s times being reported in UTC, JST, and who-knows time zones.
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### Author:  [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)
#### Post date: [March 12, 2011, 4:52am UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/2 "2011-03-12T04:52:18Z")
Well, the waves travel through deep water at about 500 mph. The epicenter was 80 miles from the nearest coast so the first waves ran ashore about 10 minutes after the quake at the nearest point (the waves slow down in shallow water and cause the water to rise).
From there you can do the math to anywhere else.
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### Author:  [@squeegee](https://boards.straightdope.com/u/squeegee)
#### Post date: [March 12, 2011, 5:05am UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/3 "2011-03-12T05:05:58Z")
> [@Whack-a-Mole](#):
>
> Well, the waves travel through deep water at about 500 mph. The epicenter was 80 miles from the nearest coast so the first waves ran ashore about 10 minutes after the quake at the nearest point (the waves slow down in shallow water and cause the water to rise).
>
> From there you can do the math to anywhere else.
Fair enough, and thanks. I was hoping there were official reports that confirmed when the quake happened (wiki says “05:46 UTC, 14:46 local time”) vs when the tsunami struck.
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### Author:  [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)
#### Post date: [March 12, 2011, 10:48pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/4 "2011-03-12T22:48:42Z")
The quake was pretty much a point-in-space / point-in-time event. e.g. It happened right \*here \*at exactly time _01:23:45_ UTC.
The tsunami “… struck the east coast of Japan” spread across a multi-hundred mile front and therefore spread over a long time span.
As \*\*Whack-a-Mole \*\*said, the closest shore & therefore first point of impact was ~80 miles & ~10 minutes. Places along the coast 160 miles away would be 10 minutes later, 20 minutes elapsed. Places 500 miles away would have been ~1 hour elapsed, etc.
If you have a specific spot on the coast in mind, the answer could be figured out easily enough.
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### Author:  [@Markxxx](https://boards.straightdope.com/u/Markxxx)
#### Post date: [March 13, 2011, 12:42am UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/5 "2011-03-13T00:42:26Z")
I watched ABC News and they reported the tsunami hit 40 minutes after the quake ended
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### Author:  [@rocking\_chair](https://boards.straightdope.com/u/rocking_chair)
#### Post date: [March 13, 2011, 2:23am UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/6 "2011-03-13T02:23:30Z")
on cnn there was one town that had video of the event. it showed people coming out of buildings after the quake, then the sirens go off for the tsunami, the people zip to and up the evac. routes, then from the overlook/road up the hillside video of the tsunami coming in and evacuees looking on.
the timing for the town was: the quake hits at 2:46 pm out at sea, (give it a few minutes to hit land), the sirens went off at 3pm, and the tsunami came in at 3:11pm.
for japan the relay goes, the quake hits, the tsunami bouy gives off the alert, people at the tsunami centre see the alert, they notify the towns, town receives the alert and sounds the warning, people zip away, tsunami hits.
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### Author:  [@Colophon](https://boards.straightdope.com/u/Colophon)
#### Post date: [March 13, 2011, 7:23pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/7 "2011-03-13T19:23:52Z")
Assuming the time stamp on the [CCTV video](http://www.youtube.com/watch?v=6FvJ62qvLBY&feature=related) is correct, the wave struck Sendai airport at 3.57pm, or 71 minutes after the quake.
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### Author:  [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)
#### Post date: [March 14, 2011, 6:59am UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/8 "2011-03-14T06:59:33Z")
> [@rocking\_chair](#):
>
> on cnn there was one town that had video of the event. it showed people coming out of buildings after the quake, then the sirens go off for the tsunami, the people zip to and up the evac. routes, then from the overlook/road up the hillside video of the tsunami coming in and evacuees looking on.
>
> the timing for the town was: the quake hits at 2:46 pm out at sea, (give it a few minutes to hit land), the sirens went off at 3pm, and the tsunami came in at 3:11pm.
>
> for japan the relay goes, the quake hits, the tsunami bouy gives off the alert, people at the tsunami centre see the alert, they notify the towns, town receives the alert and sounds the warning, people zip away, tsunami hits.
Got a link to this? It sounds interesting to see.
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### Author:  [@md2000](https://boards.straightdope.com/u/md2000)
#### Post date: [March 14, 2011, 12:29pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/9 "2011-03-14T12:29:17Z")
Keep in mind that (according to CNN and BBC) there is not “a tidal wave”, but the tsunamis come as several (very long) waves over the few hours after the quake; the first may not even be the highest, just the most spectacularly destructive.
Most of the reports on TV repeat the phrase that Sendai had “less than half an hour after the quake” before the big wave hit.
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### Author:  [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)
#### Post date: [March 14, 2011, 1:07pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/10 "2011-03-14T13:07:44Z")
> [@md2000](#):
>
> Keep in mind that (according to CNN and BBC) there is not “a tidal wave”, but the tsunamis come as several (very long) waves over the few hours after the quake; the first may not even be the highest, just the most spectacularly destructive.
Watched a show on the Indonesian tsunami and they mentioned that the second or third waves are usually bigger and more destructive than the first wave.
Even worse because after the first one people are often lulled into thinking the worst is over and return then get gobsmacked by follow-on waves. The follow-on waves might be as much as 30 minutes apart from the initial wave.
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### Author:  [@rocking\_chair](https://boards.straightdope.com/u/rocking_chair)
#### Post date: [March 14, 2011, 6:23pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/11 "2011-03-14T18:23:36Z")
> [@Cheshire\_Human](#):
>
> Got a link to this? It sounds interesting to see.
i tried poking around, but i have dial up and got frustrated.
the video was from japan’s news station with voice over english. the part at the end is what is shown the most. big huge amounts of water surging up the streets, then you see people standing by a tall rail with hillside behind them, a mother holding her daughter, a woman sitting/kneeling on the ground with a crocheted hat.
hopefully you will have better luck than i.
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### Author:  [@DrumBum](https://boards.straightdope.com/u/DrumBum)
#### Post date: [March 14, 2011, 7:09pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/12 "2011-03-14T19:09:08Z")
The seismic event was at 02:46 local time and [according to PTWS](http://ptwc.weather.gov/text.php?id=pacific.2011.03.11.073000) the first big ( 2.8m ) wave was measured at the Hokkaido station 71 minutes later.
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### Author:  [@kapri](https://boards.straightdope.com/u/kapri)
#### Post date: [March 14, 2011, 7:40pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/13 "2011-03-14T19:40:13Z")
> [@rocking\_chair](#):
>
> i tried poking around, but i have dial up and got frustrated.
>
> the video was from japan’s news station with voice over english. the part at the end is what is shown the most. big huge amounts of water surging up the streets, then you see people standing by a tall rail with hillside behind them, a mother holding her daughter, a woman sitting/kneeling on the ground with a crocheted hat.
>
> hopefully you will have better luck than i.
Maybe not this one, but this one is ☹
> **[New blast, fire fuel nuclear fears as death toll climbs in Japan](https://www.cnn.com/2011/WORLD/asiapcf/03/14/japan.disaster/index.html?hpt=Sbin)**
>
> Japanese Prime Minister Naoto Kan said Tuesday the risk of further releases of radioactive material remains "very high," as crews struggle to contain an increasingly critical crisis at a damaged nuclear plant.
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### Author:  [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)
#### Post date: [March 14, 2011, 7:47pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/14 "2011-03-14T19:47:42Z")
> [@rocking\_chair](#):
>
> i tried poking around, but i have dial up and got frustrated.
>
> the video was from japan’s news station with voice over english. the part at the end is what is shown the most. big huge amounts of water surging up the streets, then you see people standing by a tall rail with hillside behind them, a mother holding her daughter, a woman sitting/kneeling on the ground with a crocheted hat.
>
> hopefully you will have better luck than i.
I’ve seen plenty of videos, but not that one. Most of the ones I see are all the same one’s I’ve seen, already. That’s the one (that you mentioned previously) that I’ve been looking for, but no luck, either. ☹
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### Author:  [@rocking\_chair](https://boards.straightdope.com/u/rocking_chair)
#### Post date: [March 14, 2011, 8:05pm UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/15 "2011-03-14T20:05:39Z")
the beginning of the video is what gives the timing. they have shown the end of it quite a few times.
i had seen it just a few minutes before i original posted so around 9ish est on sat. night. the anchor would cut to japanese tv quite a bit during his time on cnn, the video came up during one of those times. so perhaps cnn doesn’t have rights to the whole video.
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### Author:  [@rocking\_chair](https://boards.straightdope.com/u/rocking_chair)
#### Post date: [March 16, 2011, 3:40am UTC](https://boards.straightdope.com/t/sendai-quake-how-long-before-the-tsunami-stuck/574377/16 "2011-03-16T03:40:47Z")
i saw this fellow’s video earlier on cnn. he was working with save japan dolphins. he says 8 minutes from the end of the quake to the first tsunami wave.
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