Japan's Meteorological Agency is currently testing a prototype system which detects the oh-so-subtle "P Waves" that precede the destructive "S Waves, " and alerts major operations to halt their hustle and take cover.

ENGADGET: Japan Meteorological Agency develops earthquake warning system

They discovered that by shifting the "phase" of light so that the peaks of one wave line up with the valleys of an adjacent one, the two cancel each other, creating "shadows" between waves that are smaller than the waves themselves(see diagram, p. 141).

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