Earthquake lights are lights in the sky that are associated with a severe earthquake.
History
Records of earthquakes that were accompanied by sky lights can be found in 373 BC in ancient Greek writings, that "immense columns of flame" foretold the earthquake that destroyed the cities of Helike and Bura.
However, even in the early 20th century they were still considered a myth, until photographs of actual lights were taken in Japan in the 1960s.
Appearance
The lights are most evident in the middle of the quake, although there are reports of lights that occurred after or even before the earthquake. They usually have shapes similar to those of the auroras and are white to bluish in hue, but occasionally they have been reported to have a wider color spectrum. The luminosity is typically visible for several seconds, but there have been cases in which they lasted tens of minutes.
There have been also cases in which electromagnetic waves caused by the earthquake interfered with radio transmissions, such as during the Great Chilean Earthquake of 1960.
Causes
The cause of this phenomenon is unknown, but several explanations have been suggested:
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