Earthquake Lights: Mysterious Glow That Signals Quakes Is Linked To Rift Zones
For centuries, people have been claiming to see mysterious lights on the ground and in the sky before earthquakes. Scientists viewed these claims skeptically, but with the advent of photography, the concept of pre-earthquake lights started to gain acceptance. In a study published last week in Seismological Research Letters, scientists say they've gotten a better picture of why and where these lights form.
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"When nature stresses certain rocks, electric charges are activated, as if you switched on a battery in the Earth's crust," said study author Friedemann Freund. "The charges can combine and form a kind of plasma-like state, which can travel at very high velocities and burst out at the surface to make electric discharges in the air."
Basalt and gabbro are the rocks most often associated with earthquake lights. When seismic waves stress these rocks, defects in their crystals release electrical charges. This is believed to occur when oxygen ions are released, charging pockets of air and emitting light.
The study found that earthquake lights mostly appear in continental rift environments. Of the 65 documented cases of earthquake lights since 1600 AD that were examined in the study, 85 percent of earthquake light incidents occurred on or near rifts. And 63 of the 65 earthquakes had geographic faults that were vertical, which may explain the shooting up of electrical charges from the fault up to the surface and the sky.
The right conditions for earthquake lights are only present in 0.5 percent of earthquake areas, so the lights don't happen very often. Earthquake lights seem to be most common in Italy, Greece, France, China and Japan, among other places.
Earthquake lights can take different, strange forms. During the 1906 San Francisco Earthquake, a couple claimed to have seen streams of light running along the ground two nights before the quake--about 60 miles from San Francisco. In 1988, Quebecois saw purple-pink globes of light in the sky over the St. Lawrence River, a full 11 days before an earthquake hit. In 2009, in L'Aquila, Italy, people reported seeing 4-inch high flames of light above paving stones in the town center seconds before an earthquake. And in 2008, in China, colorful earthquake lights were captured on film (see below).
Freund said that although earthquake lights are rare, if the phenomenon is observed it could serve as a warning. "If we see two, three, or four characteristic phenomena, then it looks like there might be an earthquake," Freund said. "If they are observed, let's watch out."
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