Editor’s note: Sign up for CNN’s science newsletter Wonder Theory. Explore the universe with news about fascinating discoveries, scientific advances and more.
CNN –
Reports of “earthquake lights” seen in videos recorded before Friday’s magnitude 6.8 earthquake in Morocco date back centuries to ancient Greece.
These outbreaks of bright, dancing light in different colors have long puzzled scientists and there is still no consensus about what causes them, but they are “definitely real,” said John Derr, a retired geophysicist who formerly worked at the U.S. Geological Survey. He is co-author of several scientific papers on the topic of earthquake lights (EQL).
“EQL vision depends on darkness and other favorable factors,” he explained in an email.
He said video from Morocco recently released online looked like the earthquake lights captured by surveillance cameras during a 2007 quake in Pisco, Peru.
Juan Antonio Lira Cacho, a physics professor at Peru’s Universidad Nacional Mayor de San Marcos and the Pontifical Catholic University of Peru who has studied the phenomenon, said cell phone videos and widespread use of security cameras have made earthquake lights easier to study.
“Forty years ago this was impossible,” he said. “If you saw her, no one would believe what you saw.”
Aerial photos show the extent of the damage caused by the earthquake in Morocco
Earthquake lights can take a variety of forms, says a chapter on the phenomenon co-authored by Derr and published in the 2019 edition of the Encyclopedia of Solid Earth Geophysics.
Sometimes the lights resemble ordinary lightning, or they resemble a glowing band in the atmosphere, similar to the auroras. Sometimes they resemble glowing balls floating in the air. They may also look like small flames flickering or creeping along or near the ground, or larger flames emerging from the ground.
A video taken shortly before the 2008 Sichuan earthquake in China shows glowing clouds floating in the sky.
To better understand earthquake lights, Derr and his colleagues collected information about 65 American and European earthquakes that are linked to trusted reports of earthquake 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 during earthquakes with a magnitude greater than 5.0. In most cases, the phenomenon was observed shortly before or during the seismic event and was visible up to 600 kilometers (372.8 miles) from the quake epicenter.
Particularly strong earthquakes are most likely to occur along or near the areas where tectonic plates meet. However, the 2014 study found that the vast majority of earthquakes associated with light phenomena occurred within tectonic plates rather than at their boundaries.
In addition, earthquake lights were more likely to occur on or near rift valleys, places where – at some point in the past – the Earth’s crust was torn apart, creating an elongated lowland region lying between two higher blocks of land.
Friedemann Freund, Derr’s collaborator and associate professor at San Jose University and a former researcher at NASA’s Ames Research Center, has proposed a theory for earthquake lights.
Freund explained that certain defects or impurities in crystals in rocks, when subjected to mechanical stress – such as when tectonic stress builds up before or during a major earthquake – immediately break apart and generate electricity.
Rock is an insulator that becomes a semiconductor when subjected to mechanical stress, he said.
“Before earthquakes, huge amounts of rock – hundreds of thousands of cubic kilometers of rock in the Earth’s crust – are stressed, and the stresses cause a shift in the grain size, the mineral grains relative to each other,” he added in an interview via video call.
“It’s like turning on a battery and creating electrical charges that can flow from the contaminated rock into and through uncontaminated rock. The charges move quickly, up to about 200 meters per second,” he explained in a 2014 article for The Conversation.
Other theories about what causes earthquake lights include static electricity caused by rock fracturing and radon emission, among others.
Currently, there is no consensus among seismologists about the mechanism that causes earthquake fires, and scientists are still trying to unravel the mysteries of these eruptions.
Freund hopes that one day it might be possible to harness earthquake lights or the electrical charge they cause. in combination with other factors to predict the approach of a major earthquake.