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