Sniffing Out Trouble

From renegade nations to forces of nature, how do we detect potential disasters occurring around the planet? Low frequency shock waves known as infrasound can travel great distances through the earth's crust and through oceans. Explosions tend to blast outwards in all directions evenly, producing a strong compression wave. Earthquakes, in contrast, yield strong shear waves traveling at different speeds. Just when our cold war fears have begun to subside, new threats are appearing on the horizon which will require the use of new sensing technology poised on land, sea, and in outer space to properly distinguish natural events from saber rattling adversaries.