Largest earthquake in history happened in Chile 3,800 years ago, study finds

Chile's Atacama Desert is seen in this photo from January 2021. (A. Duarte/Flickr/CC BY-SA 2.0)

A new study has found evidence that the largest earthquake in history may have been a 9.5 magnitude Chilean quake that happened nearly four millennia ago.

Researchers from Chile, the United Kingdom, Australia and France say this earthquake took place 3,800 years ago in the Atacama Desert, located in present-day northern Chile, and created tsunamis that affected coasts as far away as New Zealand and possibly Japan.

The findings were published in peer-reviewed journal Science Advances earlier this month.

According to the study, the strength of the ancient earthquake rivals the 1960 quake in Valdivia, located in southern Chile.

The Valdivia quake was estimated to have a magnitude between 9.4 to 9.6, making it the most powerful earthquake recorded. However, that earthquake had a rupture of 800 kilometres in length. This newly discovered earthquake in the Atacama Desert is estimated to have extended 1,000 kilometres.

"It had been thought that there could not be an event of that size in the north of the country simply because you could not get a long enough rupture," said James Goff, study co-author and University of Southampton visiting professor, in a press release. "But we have now found evidence of a rupture that’s about 1,000 kilometres long just off the Atacama Desert coast and that is massive.”

The researchers found large deposits of shoreline rocks deep inland, pointing to evidence of a massive tsunami. They also found ocean sediments, as well as remains of marine life that would have been swept into the desert by a tsunami.

"The Atacama Desert is one of the driest, most hostile environments in the world and finding evidence of tsunamis there has always been difficult," said Goff in the release.

"However, we found evidence of marine sediments and a lot of beasties that would have been living quietly in the sea before being thrown inland. And we found all these very high up and a long way inland so it could not have been a storm that put them there," he added.

Researchers say the earthquake and the ensuing tsunami caused "exceptional social disruption" to the hunter-gather-fisher societies that were living there at the time.

"The local population there were left with nothing,” Goff said. “Our archeological work found that a huge social upheaval followed as communities moved inland beyond the reach of tsunamis."

Goff said the people of the Atacama Desert didn't return to the coast until more than a thousand years after the quake.

"It is likely that traditions handed down from generation to generation bolstered this resilient behaviour, although we will never know for sure," he said.

On the other side of the South Pacific Ocean, researchers also found evidence in New Zealand that the tsunami may have thrown car-sized boulders hundreds of metres inland.

"In New Zealand, we said that those boulders could only have been moved by a tsunami from northern Chile and it would need to be something like a 9.5 magnitude earthquake to generate it. And now we have found it,” Goff said.

The researchers hope their findings will provide better understanding on the impacts of extreme earthquakes and underscore the importance of learning how to build a society that is resilient to such natural disasters.

"This is the oldest example we have found in the Southern Hemisphere where an earthquake and tsunami had such a catastrophic impact on people’s lives, there is much to learn from this," Goff said. "When such an event occurs next time, the consequences could be catastrophic unless we learn from these findings.”