Shortly before a powerful earthquake of magnitude 6.8 struck Morocco on Friday (8), killing more than a thousand people, mysterious glowing explosions were observed in the sky. This phenomenon, known as “earthquake lights” (EQL), dates back centuries to ancient Greece and has fascinated researchers ever since.
There is still no consensus on what causes EQLs, “but they are definitely real,” John Deere, a retired geophysicist with the US Geological Survey, said in an email to CNN. As a coauthor of several scientific articles on this phenomenon, he explains that the visibility of EQLs depends on several factors, such as local darkness.
Deere said recent videos from Morocco shared on social media are reminiscent of EQLs captured by security cameras during a 2007 earthquake in Pisco, Peru.
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Eerie blue flashes of “earthquake lights” in the sky minutes before a major quake struck Morocco. The phenomenon is thought to be a symptom of tectonic stress, but it is not understood. pic.twitter.com/MRyEzKSNVv
Euan MacDonald (@Euan_MacDonald) September 12, 2023
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Mysterious lights captured on camera shortly before the earthquake in Morocco. Climate change is certainly a strange phenomenon… pic.twitter.com/3ufFR0R5nk
Threat to Elites (@MenaceToElites) September 14, 2023
“If I told you, no one would believe it.”
Juan Antonio Lira Cacho, a physics professor at Peru’s Pontifical Catholic University (PUC) who has studied the event, says cellphones and widespread use of surveillance cameras have made it easier to study the earthquake’s lights. “Forty years ago this was impossible. If you saw them and told them, no one would believe it.”
According to Cacho, seismic lights can take a variety of forms. Sometimes they can look like regular lightning bolts, other times they can be like a glowing streak in the atmosphere, similar to the Northern Lights, or like glowing balls floating in the air. There are also those that look like small flames flickering or creeping close to the ground, or larger flames emerging from the ground.
For example, the video below, taken just before the 2008 Sichuan earthquake in China, shows glowing clouds floating in the sky.
Understanding earthquake lights
To understand earthquake lights, Deere and four other researchers collected information about 65 American and European earthquakes that were linked to reliable reports of seismic lights dating back to the 16th century. They shared their work in a 2014 paper published in the journal Seismological Research Letters.
The team found that about 80% of the EQLs analyzed occurred in association with earthquakes larger than magnitude 5. In most cases, the phenomenon was observed shortly before or during the seismic event and was visible 600 km from the epicenter of the earthquake.
Earthquakes, especially strong ones, are more likely to occur along or near 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.
Furthermore, EQLs were more likely to occur in rift valleys, i.e.
Friedemann Freund, an associate professor at the University of San Jose, California, and a former researcher at NASA’s Ames Research Center, is a coauthor of the same study. According to him, certain defects or impurities in rock crystals, when subjected to mechanical stress (e.g. during the buildup of tectonic stresses before or during a large earthquake), immediately fracture and generate electricity.
“Rock is an insulator that becomes a semiconductor when subjected to mechanical stress,” he said. “Before earthquakes, hundreds of thousands of cubic kilometers of rock in the Earth’s crust are stressed, and the stresses cause the mineral grains to shift relative to one another.”
According to Freund, it’s like turning on a battery and “generating electrical charges that can flow from loaded rocks into and through unloaded rocks at about 200 meters per second.”
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Other theories about what could be the cause of earthquake lights include static electricity caused by rock fractures and radon emission.
Freund hopes that one day it will be possible to use EQLs, or the electrical charge that causes them, in combination with other factors to predict upcoming large earthquakes.
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