Cause of Mysterious 2021 Worldwide Tsunami Discovered

Last August, a strong earthquake occurred near the South Sandwich Islands in the Atlantic Ocean. Initially, the United States Geological Survey reported that the tremor was 7.5 in magnitude on the Richter scale, before updating it to 8.2 the next day.

Scientists from the California Institute of Technology claim to have uncovered the source of a mysterious worldwide tsunami that occurred last year. The event left the researchers bewildered, as the earthquake that preceded the tsunami was too deep (47 kilometres below the Earth’s surface) to trigger it.

The study, published this week in Geophysical Research Letters, shows that the earthquake was in fact a series of sub-quakes that spread over several minutes. One of them had a magnitude of 8.2 on the Richter scale and was just 15 kilometres below the surface.

Despite its strength, the earthquake was “almost invisible” to monitoring systems because it was "buried" in the tangle of seismic waves produce by other sub-earthquakes.

Researchers believe that the "silent" tremor triggered the tsunami that rippled around the globe. It spread to the North Atlantic, Pacific, and Indian Oceans, reaching shores over 10,000 kilometres away.

Although the tsunami was small and did not cause any damage, researchers stress that such complex earthquakes can pose a significant risk.

"It's very seldom complex earthquakes like this are observed. And if we don't use the right dataset, we cannot really see what was hidden inside. We need to rethink our way to mitigate earthquake-tsunami hazards. To do that, we need to rapidly and accurately characterise the true size of big earthquakes, as well as their physical processes", said Zhe Jia, a seismologist at the California Institute of Technology.

The researchers' next goal is to automate the detection of such complex earthquakes, as is currently done for simple tremors.