The mystery tsunami traveled 6,000 miles through three oceans. Image: NOAA Center for Tsunami Research
In August of 2021, while the world was gripped by the pandemic, something very strange happened. A global tsunami traveled across the world’s oceans, going 6,000 miles through three different oceans. The strange part? There didn’t, at first, appear to be any real cause, and researchers were baffled. But now, new research recently published in journal Geophysical Research Letters might’ve found the answer: five individual sub-quakes in a row, hiding a shallower magnitude 8.2 earthquake that created the tsunami.
Just before the tsunami, seismologists recorded a magnitude 7.5 earthquake in the southern Atlantic Ocean, near the South Sandwich Islands. Although it seemed likely that it was the cause, when scientists dug deeper, they found that the quake was nearly 30 miles below the deep — far too deep to trigger a tsunami the size of the one that occurred. To make matters even more confusing, the earthquake’s rupture was nearly 250 miles long, which should have created an earthquake far larger than 7.5.
Despite researchers’ best efforts, recording earthquakes deep below the surface of the ocean isn’t an easy thing to do. According to IFL Science, current seismological techniques only take brief snapshots of the events, and the amount of information is a fraction of what researchers would like. But a few hardy researchers were determined to find out the cause of the mystery tsunami, and they dug deep into what information they had.
They found that the earthquake wasn’t a single event. Instead, it was series of sub-quakes, five in a row, that occurred over several minutes. Hidden within those was a much shallower, much slower earthquake that measured 8.2 on the Richter scale. At just 15 kilometers below the surface, it was likely the culprit of the global tsunami.
“The third event is special because it was huge, and it was silent,” said Zhe Jia, one of the researchers at the California Institute of Technology. “In the data we normally look at [for earthquake monitoring], it was almost invisible.”
Earthquake and tsunami prediction systems is important work, and Jia thinks that we have a lot of work to do. “We need to rethink our way to mitigate earthquake-tsunami hazards,” he said. “To do that, we need to rapidly and accurately characterize the true size of big earthquakes, as well as their physical processes.”
