100 years of earthquakes

This map of all the world's recorded earthquakes between 1898 and 2003 is stunning. As you might expect, it also creates a brilliant outline of the plates of the Earth's crust—especially the infamous "Ring of Fire" around the Pacific Plate.

But the real story—which Smithsonian points out and which was also the first thing I noticed—lies elsewhere. To put it colloquially: Holy shit, you guys, look at all those intraplate earthquakes!

Plate tectonics explains a lot of things, but it doesn't totally explain why earthquakes (and, in rare cases, extremely large earthquakes) happen in places far from the meeting point of two pieces of crust. There are a few possible explanations out there. We just don't know yet which one is correct.

One of the theories explaining intraplate earthquakes is based off the fact that the tectonic plates we know today have not been constant throughout Earth's history. Some of the places that are now "intraplate" were once right along fault lines. Others are at spots where continents began—and then failed—to split apart. All these things might leave behind spots of "weak" rock that's more prone to upheaval than the strong, intraplate rock around it. Studies in the 1990s found that 49% of all intraplate earthquakes happen near places like this. Of course, that leaves 51% of the shaking still unexplained.

Read more about this and other theories for why intraplate earthquakes happen.

Check out Smithsonian's write up, which includes a nice comparison between this image and a cartoon map showing the tectonic plates.

View the image, created by data visualizer John Nelson, on Flickr


  1. *clicks on image expecting some kind of animation*

    Erm, wut! So you got all the data Mr.Nelson…

    *nudge nudge*

    (disclaimer: I know nothing about data visualization)

  2. I wonder, based on that data set,  where is the most seismically active lat/lon on earth?  It strikes me you could sort by magnitude or by density,  or mash them together somehow with some sort of FEA node-averaging function..     (sigh..  the things I would study if I could go back to college)

    1. There is no evidence that certain periods of time have been more active than others.  The biggest problem is that we have not had seismometers and GPS and strainmeters for very long relative to geologic time.  So we have a 100 year snapshot of earthquake activity for our current plate tectonic arrangement.  Recently, a couple papers, and Time article by Simon Winchester argued that the recent great earthquakes (Mw 8+) are related, that the stresses are transmitted from one side of a plate to the other.  However this is not the case, the papers were well refuted, and Winchester ended up apologizing for the  article at the 2011 American Geophysical Union conference.

  3. I was looking for New Zealand, and then noticed it was there but invisible as it was completely covered in a thick bright green line. I hate earthquakes!

  4. Maggie – I am not necessarily up on every theory but I did study this stuff (my main interest and expertise is in plate tectonics), and I read the linked study to see where you’re coming from.

    While intra-plate earthquakes aren’t perfectly understood (normal earthquakes aren’t either), I’m not really sure that your characterization of their potential explanations is completely correct in the way that you’ve framed it.

    In particular, plate tectonics does fully explain intra-plate earthquakes. If you consider the arrangement of tectonic plates, you can see that they’re quite irregular in shape. The various types of plate boundaries (convergence/subduction, strike-slip, divergence) allow the irregularly shaped plates to shift and interact with each other without breaking up, but as you can imagine this isn’t perfect. 

    So, stresses can build up in the plates away from the actual boundaries because they’re being pushed/pulled from all sides. Intra-plate faults form to relieve this stress and to allow the irregularly shaped plates to morph into shape. Former plate boundaries (and failed rifts etc.) are also the result of those stresses, on a bigger scale. 

    It could also simply mean that there isn’t yet a major weakness in the crust, but the stress is so great that given a few million years, a new plate boundary will form there (or simply a major intra-plate fault). There is of course the New Madrid fault where those earthquakes occurred, for example. 

    The paper is addressing not the root cause of intra-plate earthquakes, but is looking at explanations for why the earthquakes occur in certain places instead of others. It’s also a 1999 paper written by a grad student who isn’t a geologist and predates the extensive computer modeling now used to look at tectonic stresses.

    So anyway other than earthquakes caused by magmatic activity (e.g. volcanoes), earthquakes are all due to plate tectonics. Intra-plate stresses can be modeled with relatively good accuracy, but it still isn’t easy to predict where the earthquakes will occur of course.

  5. There seems to be a disproportionately large number of kiwi boing boing readers……anyways ….yes that is us under the largest splodge of green….we are the shaky isles. (kia kaha chch)

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