Understanding the Japan Earthquake and Tsunami

Using maps and graphics, Smithsonian geologist Dr. Liz Cottrell provides an overview of the major earthquake and tsunami that struck Japan on March 11, 2011—one of the largest ever recorded globally. She explains the Pacific “Ring of Fire,” the movement of tectonic plates and subduction, the concept of earthquake magnitude, and the formation of tsunamis. Dr. Cottrell is also director of the Global Volcanism Program at the Smithsonian’s National Museum of Natural History.

UPDATE: When this video was produced, the Japan earthquake was measured at a 8.9 magnitude. Since then, USGS has upgraded the earthquake to a 9.0.

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Submitted by Anonymous (not verified) on

An annimation of the subduction/earthquake/tsunami sequence would be extremely helpful to visual, non-auditory learners! Over all the explaination was very good.

Submitted by Anonymous (not verified) on

Wow! This is a crisis but at least we can learn more about these things,lets get out there and help.

Submitted by Anonymous (not verified) on

That was educational! Tis' the earthquake is sad. Many relatives died. Well, I must say that this explains a lot of the damage. As many would say, COOL!

Submitted by Anonymous (not verified) on

i think this video was very informative and i liked how she explained the plates in the pacific ocean and how the plates took a big slide forward and caused a big huge earthquake

Submitted by Anonymous (not verified) on

Great Video - Thanks!

Submitted by Anonymous (not verified) on

i recon that was wonderful, i understood every word and i'm only 8!

Submitted by Anonymous (not verified) on

did not show the wave

Submitted by Anonymous (not verified) on

good

Submitted by Anonymous (not verified) on

please fix this we like this video

thanks

Submitted by Anonymous (not verified) on

need more examples and live footage

Submitted by Anonymous (not verified) on

Nicely done. If people don't understand after this explanatin...

Submitted by Anonymous (not verified) on

Very educational, it'll go great as a classroom tool to help explain what happened. Thanks!

Submitted by Anonymous (not verified) on

I really enjoyed your video. I think you did a great job in pulling together a lot of diverse material. I have one comment; energy release increase by about a factor of 31.6 for each increase by a factor of 1
in earthquake magnitude. This is because of a factor of 1.5 in the logarithmic relationship. This also substantiates you comment that the Magnitude 9.0 Sendai earthquake was 1000 times stronger than the Magnitude7.0 Haiti earthquake. '

Again this is a minor comment on an excellent video.

Submitted by Anonymous (not verified) on

You’ve raised an important point that might require clarification. On both the Richter scale and the preferred moment magnitude scale (or simply "the magnitude"), the amplitude - that is the shaking – goes as factors of 10. So in terms of the way people experience an earthquake, it is correct to say that a magnitude of a 9.0 earthquake is ten times greater than the magnitude of an 8.0 earthquake. The amplitude of a 9.0 earthquake is ten times greater than the amplitude of an 8.0 earthquake.

The amplitude and moment are easily quantified. The moment is the fault area multiplied by the displacement on the fault (times a number that is treated more-or-less as a constant). The area of the rupture and the displacement are easily quantified by seismologists using global data sets. This makes moment magnitude and amplitude easy to quantify. And they relate directly to the experience of people on the ground.

You are correct that the energy goes as ~32. Energy is a bit tricky to quantify because it can be released via different mechanisms (heat, motion etc...). The energy released by a quake may be experienced quite differently in different earthquakes; again, it is a much harder number to quantify.

In the video, I discuss these two quantities (magnitude and energy) in adjacent sentences and in retrospect this was confusing. It would have been clearer had I said: “A magnitude 9 earthquake is 10 times bigger--an order of magnitude bigger--than a magnitude 8 earthquake. This earthquake off the coast of Japan released 1000 times more energy than the recent earthquake in Haiti in 2010.”

-Submitted by Dr. Elizabeth Cottrell, Geologist, Smithsonian Institution

Submitted by Anonymous (not verified) on

Someone recently told me that the number of earthquakes over the magnitude of 7 has significantly increased over the last ten years. If this is true, what could be the cause? Could the upcoming solar maximum have anything to do with or other events of the solar system?

Submitted by Anonymous (not verified) on

This is a great question, and a topic of current scientific debate. Before we go into it, let me state that there is no scientific evidence, nor plausible mechanism, for the solar maximum to have any influence on terrestrial earthquakes.

Before we consult the experts, let’s gather some data ourselves. The United States Geological Survey (USGS) keeps track of earthquake locations and magnitudes. You can get them from the USGS website. Modern recording equipment has been in use since about 1900. While this may seem like long ago, this only provides a VERY short reliable earthquake record. I’ve plotted the magnitude of earthquakes (looking only at those greater than M = 5) versus time since 1900 .

The first thing to note is that, many more total earthquakes have been recorded in the last decade – that is only due to the increasing number and sensitivity of recording equipment (seismometers). We can presume that just as many earthquakes were happening in the past, but were not recorded. The second thing to note is that, over the period for which we have records, there has been no statistical increase in the number of very large (> M = 8) earthquakes in the last decade. The mean earthquake magnitude (again, looking only at earthquakes with magnitude > 5, so a small subset of all total earthquakes) on this plot is 7 and that standard deviation is 0.7 (meaning that 84% of earthquakes on this plot have magnitudes less than 7.7, and 97.6% of earthquakes on this plot have magnitudes less than 8.4). We saw “higher than average” numbers of very large quakes in the 1950s and 1960s as well and earlier in the 1900s. In fact, looking at this plot makes might make one wonder why we had so few large quakes in the 70s and 80s! So the long term record indicates that the last decade is just random statistical fluctuation in the number of earthquakes. For more on this stance, see the USGS website .

This isn’t the end of the story. Prominent seismologists have argued otherwise . On this even shorter time scale, it looks like we have an increase in the last 6 years especially .

The article I link to above proposes some mechanisms that might cause earthquakes in one location to trigger others in distant locations (to answer the “why” part of your question). However, when scientists have looked at the problem statistically, as that New Scientist article describes, there is no evidence to back this up.

-Submitted by Dr. Elizabeth Cottrell, Geologist, Smithsonian Institution