For years, scientists have been trying to trace an extremely rare “boomerang” earthquake. Now, they have recorded one for the first time in the ocean – and it’s even weirder than they expected.
Earthquakes are the result of rocks breaking into a fault, which is a boundary between two plates. A “boomerang” earthquake, also known as a “supershear rupture that spreads backwards,” means a fracture that travels away from the initial crack before returning to it at even faster speeds, scientists said.
big earthquakes are capable of destroying buildings and causing tsunamis, so understanding how they work is essential to assessing potential hazards and implementing earthquake warning systems in the future.
According to a new study in the journal Nature Geoscience, a team, led by scientists from the University of Southampton and Imperial College London, successfully recorded a magnitude 7.1 earthquake on August 29, 2016. It took place along the Romanche fracture zone, a 560 – line of fault over a mile, under the Atlantic Ocean near the equator, between Brazil and Africa.
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Scientists say earthquakes of magnitude 7 or higher are difficult to study because they often trigger a series of chain reactions across complex networks of errors. Sub-ocean faults have simple shapes, but they are located away from seismometer networks on land, so an underwater network of seismometers is needed.
The researchers said the quake traveled in a direction between the tectonic plates of South America and Africa, then shifted back to the beginning at ultra-fast speeds – breaking the “sound seismic barrier” – a boom of sorts.
An analysis revealed that the earthquake had two distinct phases. The fracture traveled up and down eastward, before suddenly turning and heading back west to the center of the fault at an accelerated speed of 3.7 miles per second.
Scientists are not exactly sure how this happened, but they believe the first phase somehow caused its most aggressive counterpart.
Only a handful of boomerang earthquakes have ever been recorded – the phenomenon has been largely theoretical, so far.
“While scientists have discovered that such a reversible rupture mechanism is possible from theoretical models, our new study provides some of the clearest evidence for this enigmatic mechanism that occurs at a true fault,” lead author Dr Stephen Hicks said. from the Department of Earth Sciences and Engineering at Imperial College London, according to a press release.
“Although the structure of the fault seems simple, the way the earthquake grew was not, and it was completely the opposite of how we expected the earthquake to look before we started analyzing the data.”
The scientists said that if a similar type of earthquake occurred on the ground, it would drastically affect the amount of earthquake – and possibly the expansion of the affected area. Successfully tracking more boomerang earthquakes will allow researchers to better predict and assess the risks from such events, improving impact predictions.