Rare ‘boomerang’ earthquake is tracked across the Atlantic ocean for the first time – shedding light on the kind of devastation these events could wreak on land
- With a boomerang earthquake the path of the quake runs back at a faster rate
- Researchers used underwater monitoring stations to track a earthquake in 2016
- The team say this helped them get a better idea of how these earthquakes work
- This will allow them to create early warning systems to look for boomerangs
A rare type of earthquake known as a ‘boomerang’ has been tracked in the ocean for the first time, and it could help scientists know how they cause devastation on land.
Scientists from the University of Southampton and Imperial College London followed the path of this type of quake that ‘runs back’ after an initial rupture in the ground.
Earthquakes occur when rocks suddenly break on a fault – a boundary between two blocks or plates – and during a large quake the breaking can spread on the fault line.
In the case of a boomerang earthquake the rupture initially spreads away from the original break but then turns and runs back the other way at higher speeds.
The strength and the duration of the rupture along the fault influences how much ground is shaken up on the surface – and the level of damage to buildings.
Knowing the mechanisms of how faults rupture and the physics involved will help researchers make better models to predict future earthquakes, the team said.
The Romanche fracture zone. A rare type of earthquake known as a ‘boomerang’ has been tracked in the ocean for the first time and it could help scientists know how they cause devastation on land.
This is a perspective view of the rocks and earthquake along the Romanche faultline
While large earthquakes occur on land and have been measured by nearby networks of monitors known as seismometers, these earthquakes often trigger movement along complex networks of faults, like a series of dominoes.
This makes it difficult to track the mechanisms of how this ‘seismic slip’ occurs.
Under the ocean, many types of fault have simple shapes, so provide the possibility get under the bonnet of the ‘earthquake engine’.
However, they are far away from the large networks of seismometers on land.
The team made use of a new network of underwater seismometers to track the Romanche fracture zone, a fault line stretching 560 miles under the Atlantic.
In 2016, the team recorded a magnitude 7.1 earthquake along the Romanche fracture zone and tracked the rupture along the fault.
This revealed that initially the rupture travelled in one direction before turning around midway through the earthquake and coming back.
During its ‘boomerang’ return run it broke the ‘seismic sound barrier’, becoming an ultra-fast earthquake, the researchers explained.
Only a handful of these earthquakes have been recorded globally.
The team believe that the first phase of the rupture was crucial in causing the second, rapidly slipping phase.
First author of the study Dr Stephen Hicks, from Imperial, said this is the clearest evidence of a boomerang rupture mechanism in a real fault.
This map shows the fault line that the ‘boomerang’ earthquake ran along – it went one way then ‘bounced back’ at a faster speed
This graph shows the interpretive cross-section along the ruptured fault plane with the colours showing the thermal profile of the rocks
‘Even though the fault structure seems simple, the way the earthquake grew was not, and this was completely opposite to how we expected the earthquake to look before we started to analyse the data.’
However, the team say that if similar types of reversing or boomerang earthquakes can occur on land, a seismic rupture turning around mid-way through an earthquake could dramatically affect the amount of ground shaking caused.
Given the lack of observational evidence before now, this mechanism has been unaccounted for in earthquake scenario modelling and hazard assessments.
The detailed tracking of the boomerang earthquake could allow researchers to find similar patterns in other earthquakes.
Doing so would allow them to add new scenarios into their modelling and improve earthquake impact forecasts.
The findings have been published in the journal Nature Geoscience.
EARTHQUAKES ARE CAUSED WHEN TWO TECTONIC PLATES SLIDE IN OPPOSITE DIRECTIONS
Catastrophic earthquakes are caused when two tectonic plates that are sliding in opposite directions stick and then slip suddenly.
Tectonic plates are composed of Earth’s crust and the uppermost portion of the mantle.
Below is the asthenosphere: the warm, viscous conveyor belt of rock on which tectonic plates ride.
They do not all not move in the same direction and often clash. This builds up a huge amount of pressure between the two plates.
Eventually, this pressure causes one plate to jolt either under or over the other.
This releases a huge amount of energy, creating tremors and destruction to any property or infrastructure nearby.
Severe earthquakes normally occur over fault lines where tectonic plates meet, but minor tremors – which still register on the Richter sale – can happen in the middle of these plates.
The Earth has fifteen tectonic plates (pictured) that together have molded the shape of the landscape we see around us today
These are called intraplate earthquakes.
These remain widely misunderstood but are believed to occur along minor faults on the plate itself or when ancient faults or rifts far below the surface reactivate.
These areas are relatively weak compared to the surrounding plate, and can easily slip and cause an earthquake.
Earthquakes are detected by tracking the size, or magnitude, and intensity of the shock waves they produce, known as seismic waves.
The magnitude of an earthquake differs from its intensity.
The magnitude of an earthquake refers to the measurement of energy released where the earthquake originated.
Earthquakes originate below the surface of the earth in a region called the hypocenter.
During an earthquake, one part of a seismograph remains stationary and one part moves with the earth’s surface.
The earthquake is then measured by the difference in the positions of the still and moving parts of the seismograph.