Lop Nor in the western provence of Xin-jiang, China, felt a 6.1 seismic event last week. Like a shot heard round the world, the tremor was easily picked up by any seismic station that was listening (Figure 1). The seismic signals were not caused by an earthquake. Nor was the source a chemical explosion caused by an industrial mining collapse that occurred in the Urals on January 5 of this year. Instead, the shock waves propagated from an underground nuclear test—estimated to be China's 42nd nuclear test of record. The explosion, which occurred about a kilometer or so down in the Earth's crust, was on par with that of 40 to 150 kilotons of TNT (Figure 2).