Editor’s Note: Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advances, and more.
Reports of “earthquake lights,” like those seen in videos captured before Friday’s 6.8 magnitude earthquake in Morocco, date back centuries to ancient Greece.
These bursts of bright, dancing light in different colors They have long puzzled scientists, and there is still no consensus on what causes them, but they are “definitely real,” said John Derr, a retired geophysicist who worked at the U.S. Geological Survey. He has co-authored numerous scientific papers on seismic lights, or EQLs.
“Seeing the EQL depends on darkness and other favorable factors,” he explained in an email.
He said recent video from Morocco shared online looked like earthquake lights were captured by security cameras during a 2007 earthquake in Pisco, Peru.
Juan Antonio Lira Cacho, a physics professor at the Universidad Nacional Mayor de San Marcos in Peru and the Pontifical Catholic University of Peru, who has studied the phenomenon, said cellphone videos and the widespread use of security cameras have made studying earthquake lights easier.
“Forty years ago it was impossible,” he said. “If you saw them no one would believe what you saw.”
Earthquake lights take on different shapes
Earthquake lights can take different forms, according to a chapter on the phenomenon written by Derr and published in the 2019 edition of the Encyclopedia of Solid Earth Geophysics.
Sometimes, the lights can appear similar to ordinary lightning, or they can be like a bright band in the atmosphere similar to the aurora. Other times they resemble glowing orbs floating in mid-air. They may also look like small flames flickering or crawling along or near the ground or larger flames emerging from the ground.
A video shot in China shortly before the 2008 Sichuan earthquake shows bright clouds floating in the sky.
To better understand seismic lights, Derr and his colleagues collected information on 65 American and European earthquakes associated with reliable reports of seismic lights dating back to the 1600s. They shared their work in a 2014 paper published in the journal Seismological Research Letters.
The researchers found that about 80% of the EQL events studied were observed for earthquakes greater than magnitude 5.0. In most cases, the phenomenon was observed shortly before or during the seismic event and was visible up to 600 kilometers from the earthquake’s epicenter.
Earthquakes, particularly powerful ones, are more likely to occur along or near areas where tectonic plates meet. However, the 2014 study found that the vast majority of light-related earthquakes occurred within tectonic plates, rather than at their boundaries.
Additionally, earthquake lights were more likely on or near Rift Valleys, places where – at some point in the past – the Earth’s crust had been torn apart, creating an elongated plain region that sits between two higher blocks of land.
Possible causes of seismic lights
Friedemann Freund, Derr’s collaborator and adjunct professor at the University of San Jose and a former researcher at NASA’s Ames Research Center, has developed a theory for seismic lights.
Freund explained that when certain defects or impurities in rock crystals are subjected to mechanical stress – such as during the buildup of tectonic stresses before or during a strong earthquake – they instantly break down and generate electricity.
The rock is an insulator that, when mechanically stressed, becomes a semiconductor, he said.
“Before earthquakes, huge volumes of rock – hundreds of thousands of cubic kilometers of rocks in the Earth’s crust – are subjected to stress, and the stresses cause mineral grains to shift relative to each other,” he added in an interview via video call.
“It’s like turning on a battery, generating electrical charges that can flow from stressed rocks into and through unstressed rocks. The charges travel fast, up to about 200 meters per second,” he explained in a 2014 article for The Conversation.
Other theories about the causes of seismic lights include static electricity produced by fracturing rock and radon emanation, among many others.
There is currently no consensus among seismologists on the mechanism that causes earthquake lights, and scientists are still trying to unravel the mysteries of these explosions.
Freund hopes that one day it may be possible to use seismic lights, or the electrical charge that causes them, in combination with other factors to help predict the approach of a large earthquake.
For more CNN news and newsletters, create an account at CNN.com