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Want to know when an earthquake is afoot?
Watch for the lights.
Geologists say they have proof of a rare, elusive phenomenon called "earthquake lights," according to USA Today, when "balls of light" or reverse lightning shoot out of the ground before a temblor hits.
A team of researchers -- including a scientist working at San Jose State University and NASA Ames Research Center in Mountain View -- have documented the phenomenon, often dismissed as a hallucination, at least 65 times since 1600. Their study appears in the journal Seismological Research Letters.
Rumors of light emitted during earthquakes have been around for centuries and have sometimes sparked UFO reports, USA Today reported.
In 2009, flames were seen in Italy seconds before a quake -- and security cameras in Peru recorded blue lights in 2007.
The lights occur only in areas that have certain types of rock as well as deep vertical faults, the researchers say.
That means "less than 0.5 percent" of earthquakes will have lights.