'Boomerang' Earthquake Discovered Under the Atlantic Ocean

Scientists witnessed a 'boomerang' earthquake under the Atlantic Ocean fault line which provided signs on how it could cause devastation on land.

The temblor shot eastward across a deep gash in the seafloor, and then dashed back to where it started at incredible speeds. It went remarkably fast and created the geologic version of a sonic boom.

Earthquakes Usually Travel in One Direction or Do They?

Scientists have always been intrigued by talks of "boomerang" earthquakes in which seismic reverberations move in one direction, and then back.

The "back-propagating rupture" was identified by submerged seismometers that monitor a fracture zone close to the Mid-Atlantic Ridge. It can be challenging to understand the precise mechanics of earthquakes on land, where fault networks are complicated.

Underwater faults tend to be more direct, which is the reason researchers wanted to study the nearly straight Romanche Fracture Zone, which divides the Mid-Atlantic Ridge.

Subduing the Seismic Sound Limit

While enormous (magnitude 7 or higher) earthquakes transpire on land and have been measured by nearby networks of monitors (seismometers), these earthquakes usually activate movements along with complex networks of faults, like a series of dominoes.

In 2016, they recorded a magnitude 7.1 earthquake along the Romanche fracture zone and tracked the rupture along the fault. This explained that initially the rupture moved in one direction before turning around halfway through the earthquake and breaking the 'seismic sound barrier', thereby becoming an ultra-fast earthquake.

Only a few such earthquakes have been recorded globally. The team believes that the first stage of the rupture was crucial in prompting the second, rapidly slipping state.

A Bevy of Boomerangs

Understanding why and when these boomerang cases take place is essential to grapple with the various risks earthquakes present. Shaking from a quake can focus near one the end of the fault, in the direction the temblor is travelling.

Seismologist Lingsen Meng of the University of California, Los Angeles, said it was like the Doppler Effect. While this focused shaking is normally considered to occur in one direction, a boomerang could focus shaking in two opposite zones.

The Big Question Remains: How Often Does This Happen?

A boomerang tremor at super shear speeds, as the team perceived in the Atlantic, is perhaps a fairly rare breed. "To the best of my knowledge, this is the first time it has been reported," says geophysicist Yoshihiro Kaneko of GNS Science in New Zealand.

But more extensive evidence of boomerang quakes is arising. These back-tracking developments have been analyzed in computer models and simulated in lab experiments.

"The theory says that it's there, but it's quite difficult to see that [in the real world]," says geophysicist Louisa Brother son, a Ph.D. researcher at the University of Liverpool in the U.K., who simulates earthquakes in the lab.

Although it isn't clear how often boomerang earthquakes occur, understanding that could benefit researchers in learning how to detect on land and to predict as well as warn about super shear earthquakes and other temblors.

Direction-switching earthquakes may still be rare, but now that one has been spotted, the door is open to a more comprehensive understanding of how Earth shimmies and shakes.

These boomerangs may be hidden by common techniques used to analyze quakes, which are rooted in an assumption that a temblor rushes in one direction.

"Naturally we're not looking for it, we don't expect it to exist," says seismologist Jean-Paul Ampuero of the Université Côte d'Azur in France. Yet for earthquakes, it appears, complexities might be a norm rather than an exception.

Written by- Anusha Vajha

Edited by – Adrija Saha

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