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‘Boomerang earthquakes’ may mean one earthquake can strike twice

Researchers used a GIF to demonstrate the boomerang earthquake effect. Screen grab from GIF, Imperial College of London

    (CNN) — Can an earthquake turn around and strike twice? New research has some seismologists saying yes.

Tremor data from a 2016 earthquake at the South American and African tectonic plates, deep below the Atlantic Ocean, showed the quake first rushed northeast, then unexpectedly turned and struck the fault line again going west, according to a study published Monday in the journal Nature Geoscience.

The episode, in an area known as the Romanche fracture zone, is visualized in this graphic animation from Imperial College London.

via GIPHY

What is a boomerang earthquake?

The research team used underwater seismometers to pull data on the 2016 quake, Stephen Hicks, a lead researcher on the study, explained in a series of tweets.

Research “shows the rupture initially going east, then mid-way through the quake, it turns around & travels west. A remarkable result and why we call this the ‘boomerang’ earthquake,” Hicks tweeted.

Beyond the initial discovery, the research informs how seismic events can move and change.

“Scientists and the people using hazard maps both benefit from learning that earthquake faulting has a wide variety of ways to unfold than previously documented,” said John Vidale, a University of Southern California professor who was unaffiliated with the study.

The so-called “boomerang earthquake” may be among the first of its kind.

“There are some hints that a small number of these reversing earthquake ruptures have appeared on land, but thorough evidence is scant,” Hicks said, “so I think our study probably provides the clearest example of one so far.”

Double quakes could cause stronger tremors on land

Hicks cautions that because evidence is so sparse, this finding does not mean those living near earthquake hot spots should start prepping for double quakes.

“We’re not sure if what we have observed along a specific type of plate boundary may also occur on different fault types on land,” he said.

If this type of earthquake were to occur on land, Hicks said, it could cause stronger tremors, as the direction of a quake can impact its strength.

“However, since we have only measured one of these types of earthquake in detail, then it will probably require more scientific analysis of other earthquakes before our result starts to directly impact models of seismic hazard and their mitigation,” he said.

Documentation in the recent study of both a change in direction and faster-than-expected rupture speed “challenges our ability to understand how friction operates and also to forecast the shaking expected in future earthquakes,” Vidale said.

It is also significant that the study highlights this quake as moving at “supershear” speeds.

A supershear event is an earthquake that moves so quickly that it causes the geologic version of a sonic boom. Though incredibly rare, these events can cause significant damage. The 2018 Indonesian quake in Sulawesi, which caused a tsunami, is suspected to have been a supershear event.

The-CNN-Wire
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