Archaeologists have found evidence of the largest known earthquake in human history – a terrifying 9.5 magnitude mega-earthquake that caused an 8,000 kilometer long tsunami and prompted human populations to abandon nearby coasts for 1,000 years, new study finds.

The earthquake struck about 3,800 years ago in what is now northern Chile when a tectonic plate rupture raised the coastline of the region. The tsunami that followed was so powerful that it created waves reaching 20 meters and reached as far as New Zealand, where it threw rocks the size of cars hundreds of kilometers away. inland, the researchers found.

So far the biggest earthquake never recorded is the Valdivia earthquake in 1960, which struck southern Chile with a magnitude between 9.4 and 9.6, killing up to 6,000 people and sending tsunamis raging across the Pacific Ocean. The rupture that caused the Valdivia earthquake was huge, stretching up to 800 km in length. But, as scientists detail in research published April 6 in the journal Scientists progressthe recently discovered ancient megaquake was even larger, originating from a rupture about 1,000 km long.

Related: Strange earthquakes in South Carolina attributed to a man-made lake

“We had thought there couldn’t be an event of this magnitude in the north of the country simply because we couldn’t get a break long enough,” co-author of the study James Goff, a geologist at the University of Southampton in England, said in a press release.

Like the Valdivia earthquake, the ancient earthquake was a megathrust earthquake, the strongest type of earthquake in the world. These earthquakes occur when one of the Earth tectonic plates are forced or subducted under another. The two plates eventually lock into place by friction, but the forces that caused the plates to collide continue to build. Eventually, such tension builds up that the point of contact between the plates tears apart, creating a gigantic rupture and releasing energy in the form of devastating seismic waves.

Evidence of the giant quake has been found in marine and coastal features – such as littoral deposits (rocks, pebbles and sand native to coastal regions) and sea rocks, shells and marine life – which researchers have discovered displaced far inland from Chile. Atacama Desert.

“We found evidence of marine sediments and many beasts that would have lived quietly in the sea before being thrown inland,” Goff said in the statement. “And we found all of those way up and way inland, so it couldn’t have been a storm that put them there.”

To better understand what drove these deposits away from the sea, the researchers used radiocarbon dating. This method consists of measuring the quantities of carbon 14, a radioactive carbon isotope, found inside a material to determine its age. Since carbon-14 is everywhere on Earth, deposits easily absorb it during their formation. The half-life of carbon-14, or the time it takes half of it to radioactively decay, is 5,730 years, making it ideal for scientists looking to look back over the past 50,000 years. of history by checking the amount of undecomposed carbon 14 a material a.

After dating 17 deposits at seven separate dig sites along 600km of Chile’s northern coast, the researchers found that the age of the displaced coastal materials suggested they had been washed inland around 3,800 years old.

Other evidence also came in the form of ancient stone structures that archaeologists excavated. These man-made stone walls were found under the tsunami deposits, and some were upside down, pointing out to sea, suggesting they had been knocked down by the strong currents of the tsunami surf.

“The local people there have nothing left,” Goff said. “Our archaeological work has revealed that enormous social upheaval ensued as communities moved inland, out of the reach of the tsunamis. It took more than 1,000 years before people returned to live on the coast, which is an incredible amount of time given that they depended on the sea for food.

As this is the oldest known discovery in the Southern Hemisphere of an earthquake and tsunami devastating human lives, researchers are excited to probe the region further. They think their research could better inform us of the potential dangers of future earthquakes.

“Although it had a major impact on Chileans, the South Pacific islands were uninhabited when they were hit by the tsunami 3,800 years ago,” Goff said. “But they are all well populated now, and many are popular tourist destinations. So when such an event happens next, the consequences could be catastrophic unless we learn from these findings.

Originally posted on Live Science.