Scientists spot rare ‘boomerang earthquake’ in the ocean – BGR

• Scientists have gathered the first evidence of a so-called ‘boomerang earthquake’ that occurred deep in the Atlantic Ocean.
• A boomerang occurs when a fracture continues in one direction before the course changes rapidly and travels at even higher speeds in the opposite direction.
• The researchers hope these observations can better help prepare early warning systems and models for earthquake damage.

---

Earthquakes are relatively well understood as a natural phenomenon. They occur when pressure builds up between two pieces of the earth’s crust and then eventually release, causing intense shaking to cause serious damage when it occurs near a populated area. They range in intensity from incredibly mild to absolutely catastrophic, but a new study reveals some delaying details about one of the rarer types of earthquakes.

Scientists call it a boomerang earthquake, and the name tells you a lot about how it works. The shaking begins along a fault line between two pieces of the earth’s surface, traveling in one direction along the fault before reversing abruptly. This almost never happens, but when it does, the return of the fracture occurs at unusual speeds, and researchers have recently recorded one as it happened.

As researchers report in a new study published in Nature Geoscience, a magnitude 7.1 earthquake in the Atlantic Ocean back in 2016 turned out to be one of those rare earthquakes. The earthquake was detected with underwater seismic sensors, and it appeared to move first in one direction before switching back quickly and breaking even more in the opposite direction at an incredibly fast speed.

“Although scientists have found that such a mechanism for reversible fracture is possible from theoretical models, our new study provides some of the clearest evidence for this enigmatic mechanism occurring in a real error,” said Drs. Stephen Hicks, first author of the study, in a statement. “Even though the error structure seems simple, the way the earthquake did not grow, and this was in stark contrast to how we expected the earthquake to look before we started analyzing the data.”

The researchers believe that this phenomenon is quite rare, but as a result, it has also not been widely studied. The fact that this kind of thing can happen is not considered in models that predict earthquakes and is certainly not made responsible in early warning systems and other networks of information designed to keep people safe.

The “back implantation” of the fracture is thought to be linked to deep splits that reach weak areas of the fault and then snap back in the opposite direction.

“We suggest that deep fracture in weak fault segments facilitated a larger seismic slip on shallow closed zones,” the researchers write. “This emphasizes that even earthquakes along a single distinct fault zone can be highly dynamic. Observations of retrograde fractures are regrettable, and the possibility of reverse propagation is largely absent in rupture simulations and is not explained in hazardous assessments. ”