North Korea's nuclear bomb test

I'm not a big fan of politics, but part of the story about North Korea's second nuclear bomb test caught my eye.

North Korea announced its underground nuclear test a little more than an hour after the U.S. Geological Survey reported a magnitude 4.7 seismic disturbance at the site of North Korea's first nuclear test. --CNN

And sure enough, here's the earthquake data from the USGS.