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Andrew Alden

Japan Hit by M 8.9 Quake [updated]

By March 11, 2011

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Eastern Honshu, Japan's largest island, was devastated by a great (M 8.9) earthquake at 2:45 pm Friday local time. It was a classic subduction thrust event, and a 4-meter tsunami washed over the Japanese coast. Tsunami waves have affected most of the Pacific rim. [Update: Chris Rowan discusses the scientific details of this typical subduction-zone event. And Erik Klemetti addresses the persistent claim that the Moon influenced this quake. And the US Geological Survey has issued new estimates putting the magnitude as high as 9.1, making it the fifth largest ever recorded by seismographs.]

The USGS notes that this quake had foreshocks starting two days beforehand. The first of these was a M 7.1, coincidentally the same size as the largest aftershock so far. Of course, no one could definitively say that they were foreshocks at the time, because there's no way known to distinguish them from ordinary earthquakes.

The USGS' automated PAGER system estimated that more than 4 million people were subjected to very strong (intensity VII) shaking, and that Tokyo and Yokohama, with their 12 million inhabitants, felt strong (VI) shaking. The model estimated that there have been on the order of 100 deaths from the earthquake; this does not include the tsunami.

Google has erected a crisis response page for this earthquake. It includes a "person finder." And my colleague, Japan Travel Guide Shizuko Mishima, has links to Japanese news sources.

Japan has been preparing for events like this for more than 30 years. Its "design quake," called the Tokai Earthquake, is one that appears to recur regularly farther south near Tokyo. But the lessons learned from Tokai planning are applied all over the country. In America we can anticipate a similar earthquake, in size and effects, somewhere in the Cascadia subduction zone on the century scale.

USGS page for this earthquake
Japan earthquake agency page for this event
About earthquakes
About subduction
Earthquake preparation in Japan
Earthquakes in Cascadia
About tsunamis


March 12, 2011 at 7:30 pm
(1) Shawn says:

Japan always good at preparing any natural disasters. Can earthquake cause nuclear plant explosions? Japan is so peaceful and nuclear plants had never had good terror security systems. Wasn’t this a planed explosion by somebody? They refused to have nuclear plans at beginning, however, some county sold the system. Japan seems a free independent country, however, they have to obey because they lost a war. This earthquake is very strange, too. Now days, earthquakes can be created such as by “HAARP.” Some counties and somebody did not like Japan tried to fight back for their freedom from being controlled. They already had very big damages. I like to pray for peace and early recovery in Japan.

March 12, 2011 at 10:16 pm
(2) Geology Guide says:

Shawn, be careful about what you read. Nuclear plants are very complicated machines that don’t like being shaken hard, so yes, earthquakes can really mess one up even though they’re extremely well built. The rest of your post, except the last sentence, is paranoid misinformation.

March 15, 2011 at 11:55 am
(3) Dave Trimmer says:

Thank you for the info. However, I am not sure just what happened. Did the quake occur off shore some distance and shake the island? If it happened off shore, did it cause a deep underwater canyon that filled up immediately causing the big wave? There are a lot of rumors floating around and it is hard to get to the truth. Please help if you care to. Thank you.

March 15, 2011 at 1:51 pm
(4) Geology Guide says:
March 17, 2011 at 2:13 pm
(5) Zai says:

do you expect for upcoming aftershock regarding to their (Japan) nuclear blasted? Nuclear blast could create EQ & in my theory, there will be a great EQ gonna be happened & my target either San Andreas Fault or somewhere in Pacific Ring of Fire due to perigee moon. It could be happened on next week due to lunar cycle, the full moon is on March 21st 2011.
Ironically, moon’s gravity will influent the Earth mantle cycle ~ the cycle will be interrupted & there will be the greatest EQ with higher Richter Scale reading which will change to the world map, again.
My point is, the Pacific slab is less dense to Atlantic slab & the very active tectonic process is located in San Andreas Fault which is very potential to create The Greatest EQ & that could change the world map ~ Look! who’s got new neighbour???
Just in case the aftershock happen or the interrupted cycle could bring into intra oceanic thrusting. As a result, Mt. Kinabalu in Borneo will become more higher same goes to Mt. Averest.
p/s: Currently I’m pursuing Degree in Geology & this’s just my theory according to my geological knowledge.


March 17, 2011 at 2:27 pm
(6) Geology Guide says:

Zai, your comment makes no sense. When you learn a little more in your degree program, you’ll understand some of the errors in your thinking. In the meantime, I urge you to stop trying to create grand theories that predict cataclysms.

March 17, 2011 at 11:49 pm
(7) salina says:

hi… I am planning to visit Japan in Month of October. Is it safe by that time? or should I cancel and go to elsewhere???
About the radiation etc.. if I decided to visit in October, is it safe? Please advise.


March 18, 2011 at 2:36 pm
(8) Geology Guide says:

Salina, outside of northern Honshu life in Japan is normal. An ordinary airline flight exposes you to more radiation than you will get near those reactors, unless you’re a kilometer or so away, and no one will let you that close.

Japan’s big problem right now is not radiation, it’s having northeastern Honshu in shambles. But there is a lot more to see in Japan elsewhere in the islands. I expect the Japanese to be welcoming every visitor they can get, and you should have a good time if you go there this fall.

July 12, 2011 at 4:28 pm
(9) Mike says:

Good to hear that life is back to normal in Japan and that we arent getting any nuclear particles over here in America! phew! Some were talking it could reach here!

July 14, 2011 at 11:41 pm
(10) netbooks under 200 says:

I wouldn’t say things are back to normal. They still have lots of work to do up there. For the most part though, I’d say they are recovering pretty well.

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