(credit: (stephan))
Just last week we had occasion to mention that seismometers are used to detect secret nuclear weapons tests as well as earthquakes. (That mention came in a story about seismometers detecting munitions explosions during fighting in Baghdad in 2006.) This week, we’ve seen this detection in action.
Around 8:30pm EST Tuesday, seismometers around the world detected what appears to be an underground detonation of an atomic bomb in North Korea. The event, which was equivalent to about a magnitude 5.1 earthquake, occurred at a shallow depth in the same location as previous tests in 2006, 2009, and 2013—a region that doesn’t see many earthquakes.
The #seismic signals of today's event in North Korea are similar to those detected on 12 Feb 2013 #CTBT http://pic.twitter.com/KeLT7G9t2V
— CTBTO (@ctbto_alerts) January 6, 2016
The seismic signals of these explosions differ from those produced by earthquakes. Earthquakes release compressional waves as well as shear waves produced by the sliding motion along a fault. Those waves travel through the body of the Earth, arriving at slightly different times. The real damage in an earthquake comes from waves that travel along the surface of the Earth and are the last to arrive.
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