"GPS satellites carry a set of nuclear detonation detectors consisting of an optical sensor (Y-sensor), an X-ray sensor, a dosimeter, and an electromagnetic pulse (EMP) sensor (W-sensor), that form a major portion of the United States Nuclear Detonation Detection System" http://en.wikipedia.org/wiki/Global_Positioning_System
The approach in the article is in fact quite novel, though.
They're actually detecting the shock wave in the atmosphere. Not even something "easy" like the seismic shock wave.
The same idea has recently been used to improve weather forecasts for a few years now (http://en.wikipedia.org/wiki/GPS_meteorology).
Differences in atmospheric gas density affect the propagation speed of the GPS radio signal. Peering thru the edge of the atmosphere at the constellation of GPS transmitters allows you to get a bunch of density/temperature profiles in a way that's immune to some instrumental artifacts of other instruments.
One of the inventors of the idea formed a company to cooperatively launch small satellites to do these retrievals: