Seismic signals are generated by natural events, such as earthquakes, and by nuclear explosions, such as the recent tests in India and Pakistan. They are also generated by chemical explosions associated with mining. A new report from a National Research Council committee reviews a draft report by a U.S. Department of Energy (DOE) working group that describes the nature of seismic signals from mining operations and possible measures that could help distinguish between seismic signals from legitimate mining operations and those from covert nuclear tests.