Plate Tectonics and the Earthquake in Japan

Posted March 11, 2011

by Lensyl Urbano

The magnitude 8.9 earthquake that devastated coastal areas in Japan shows up very clearly on the United States Geologic Survey’s recent earthquake page.

The big red square marks an aftershock of the magnitude 8.9 earthquake off Japan. (Image via USGS). Note that most of the earthquakes occur around the edge of the Pacific Ocean (and the Pacific Plate).

Based on our studies of plate tectonics, we can see why Japan is so prone to earthquakes, and we can also see why the earthquake occurred exactly where it did.


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The obvious trench to the east and the mountains and volcanoes of the Japanese islands indicate that this is a convergent margin. The Pacific plate is moving westward and being subducted beneath the northern part of Japan, which is on the Okhotsk Plate.

The tectonic plates and their boundaries surrounding Japan. The epicenter of the earthquake is along the convergent margin where the Pacific Plate is being subducted beneath the Okhotsk Plate. Image adapted from Wikimedia Commons user Sting.

The epicenter of the earthquake is on the offshore shelf, and not in the trench. Earthquakes are caused by breaking and movement of rocks along the faultline where the two plates collide.

In cross-section the convergent margin would look something like this:

Diagram showing the tectonic plate movement beneath Japan. Note the location of the earthquake is beneath the offshore shelf and not in the trench.

The shaking of the sea-floor from the earthquake creates the tsunamis.

So where are there similar tectonic environments (convergent margins)? You can use the Google Map above to identify trenches and mountain ranges around the world that indicate converging plates, or Wikimedia Commons user Sting’s very detailed map, which I’ve taken the liberty of highlighting the convergent margins (the blue lines with teeth are standard geologists’ markings for faults and, in this case, show the direction of subduction):

Convergent plate boundaries (highlighted blue lines) shown on a world map of tectonic boundaries. The blue lines with teeth are standard geologic symbols for faults, with the teeth showing the direction of the fault underground. Image adapted from Wikimedia Commons user Sting.

The Daily Dish has a good collection of media relating to the effects of the quake, including footage of the tsunami inundating coastal areas.

Cars being washed away along city streets:

Our thoughts remain with the people of Japan.

UPDATES:

1. Alan Taylor has collected some poignant pictures of the flooding and fires caused by the tsunami and earthquake. TotallyCoolPix has two pages dedicated to the tsunami so far (here and here).

2. Emily Rauhala summarizes Japan’s history of preparing for this type of disaster. They’ve done a lot.

3. Mar 12, 2011. 2:10 GMT: I’ve updated the post to add the map of the tectonic plates surrounding Japan.

4. A CNN interview that includes video of the explosion at the Fukushima nuclear power plant (my full post here).

5. NOAA has an amazing image showing the tsunami wave heights.

Tsunami wave heights modeled by NOAA. Note the colors only go up to 2 meters. The maximum wave heights (shown in black in this image), near the earthquake epicenter, were over 6 meters.

They also have an excellent animation showing the tsunami moving across the Pacific Ocean. (My post with more details here).

6. The United States Geological Survey (USGS) put out a podcast on the day of the earthquake that has interviews with two specialists knowledgeable about the earthquake and the subsequent tsunami, respectively. Over 250 kilometers of coastline moved in the earthquake which is why the tsunami was so big. They also have a shakemap, that shows the area affected by the earthquake.

USGS ShakeMap for the earthquake. Image via the USGS.

7. ABC News (Australia) and Google have before and after pictures.

8. The University of Hawaii has a page about, Why you can’t surf a tsunami.

9. A detailed article on earthquake warning systems, among which, “Japan’s system is among the most advanced”, was recently posted in Scientific American.

10. Mar 15, 2011. 9:15 GMT: I’ve added a map of tectonic boundaries highlighting convergent margins.

Shinmoedake Volcano.

11. The Shinmoedake Volcano erupted two days after the earthquake, but they may be unrelated.

Fukushima reactor status as of March 16th, 5:00 pm GMT from the Guardian live blog.

12. The Guardian’s live blog has good, up-to-date information on the status of the nuclear reactors at Fukushima.

Citing this post: Urbano, L., 2011. Plate Tectonics and the Earthquake in Japan, Retrieved September 25th, 2017, from Montessori Muddle: http://MontessoriMuddle.org/ .
Attribution (Curator's Code ): Via: Montessori Muddle; Hat tip: Montessori Muddle.

9 Responses to “Plate Tectonics and the Earthquake in Japan”

  1. Heather Gingerich

    Hello! I am a geologist and my children attend the Montessori School of Ingersoll (Ontario, Canada) and although I have have often lamented the lack of “official” materials for the earth sciences (decided to make some myself), I have to say that this website is inspiring. Well done and thank you!

  2. Lensyl Urbano

    Thanks. I’m originally a geologist by training, so I really appreciate the comment. Also, if you’d like to share some of your earth science materials, drop me a line.

  3. Monkey Boy

    nice website very informational

    thank you

  4. Houria Remili

    Excellent website, Very informational and helpful
    thank you :)

  5. mario

    gracias por darme las respuestas para mi clase de geografia de zamora

  6. mohammad atashin

    excellent & very helpful
    tanks a lot

  7. Lauren S

    Thanks for the information, I needed it for a school project :)

  8. Saurav R.

    Thanks for the information, I needed it for a school project. I attend Saint Mary’s College, Trinidad and I am in Form 3 and this website would really help me get an A+

  9. Lensyl Urbano

    Thanks for the information, I needed it for a school project. I attend Saint Mary’s College, Trinidad and I am in Form 3 and this website would really help me get an A+

    Neat. I went to Naparima.

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