A magnitude 7.1 earthquake hit Acapulco, in southern Mexico, on Tuesday (7), killing at least one person. As had already happened, during another earthquake in Mexico in 2017, something very unusual happened.
Lights similar to those of an aurora borealis were recorded, according to reports from residents on social networks and reports from local press vehicles.
But what are these mysterious flashes of light? And what do they have to do with the earthquake?
According to researchers at Rutgers University in the United States, these lights appear due to movements in soil layers, which generate enormous electrical charges when they happen near Earth faults.
They are known as “earthquake lights” and have been documented since the 1600s, according to a statement from the Seismological Association of the United States.
Two days before the 1906 San Francisco earthquake, for example, a couple saw rays of light in the sky. In 1998, a glowing globe of pink and purple lights was seen 11 days before a devastating earthquake in Quebec, Canada.
Just before the 2009 earthquake in L’Aquila, Italy, passersby saw “flames of light” rising from the cobblestones in the historic city center just seconds before the quake.
Security cameras also recorded beams of light during the 2007 magnitude 8.0 earthquake in Pisco, Peru.
Several videos posted on YouTube show spheres of light at the time of the earthquake followed by the tsunami in Fukushima, Japan, in 2011. And now something similar is happening in Mexico.
These earthquake lights can come on before or during seismic movements.
The most common lightning strikes in the sky are the result of an accumulation of electrical charge in the clouds. But laboratory experiments at Rutgers University indicate that these lights actually originate from the increase in electrical charge in the ground when cracks appear in the ground.
The results were presented at a meeting of the American Society of Physics by biomedical engineer Troy Shinbrot, in 2014.
His lab has created a miniature model of the stresses, forces, and disruptions that occur during an earthquake.
They filled tanks with different substances, from flour to small glass balls, and shook them over and over in order to create cracks.
The observation of this phenomenon indicated that friction caused hundreds of volts of electricity, suggesting that even subtle ground movements in fault lines are enough to charge the Earth and cause lightning in the sky.
“We took a pot full of flour and shook it until cracks appeared – this produced 200 volts of energy,” said Shinbrot.
The team led by Troy Shinbrot has also observed two other types of particulate materials that stick together and slide in an Earth-like manner in areas more prone to earthquakes.
So they found that when they were moved, they all developed an electrical voltage, which can be much higher if it happens in the midst of geological faults.
“I don’t know a mechanism that can explain this, it seems to be a new kind of physics,” he said.
Warning to prevent disasters
There is still no explanation for the reasons behind the formation of this charge or why the lights appear sometimes and not others.
“Not every major earthquake is preceded by lightning. Not every lightning strike that hits the sky will be followed by an earthquake,” said Shinbrot.
“We noticed that the lights seem to predate some big earthquakes of magnitude 5 or bigger. But the voltage isn’t always the same. Sometimes it’s high, and sometimes it’s low,” he added.
Still, these flashing warning signs could help prevent disasters.
In the case of the L’Aquila earthquake, one resident is known to have seen lights from inside his house two hours before the earthquake and taken his family to safety.
After that, projects emerged to observe and record these lights in regions especially vulnerable to seismic movements.
* This article was published on September 8, 2017, after an earthquake measuring 8.2 in Mexico. It is being republished and updated now, in 2021, because the mysterious phenomenon flashes of light repeated in another earthquake this week.