An earthquake occurs when a rock suddenly breaks on a fault – the boundary between two blocks or plates. During major earthquakes, the break of rock can spread down the fault line. Now, geological scientists have recorded a ‘boomerang’ earthquake in the equatorial Atlantic, where the rupture initially spread out from the original break but then turned and ran back in the other direction. with higher speed.
While large earthquakes (7 magnitude or more) occur on land and are measured with nearby seismic networks, these often trigger motion along complex fault networks. trash, like a series of domino pieces.
This makes it difficult to follow the basic mechanisms of how this ‘seismic slip’ occurs.
On the ocean floor, many types of faults have a simple shape, so are likely to be under the bonnet of the ‘earth maneuver’. However, they are far from large land-based seismic networks.
Dr. Stephen Hicks from Imperial College London and the University of Southampton used a new network of underwater seismographs to track the Romanche Fracture, a fault line that spans 900 km (559 miles) below the Atlantic. Equator.
In 2016, researchers recorded a magnitude 7.1 earthquake along the fault zone and tracked the fault along the fault zone.
This suggests that the fracture initially moves in one direction before spinning between the earthquake and breaks the ‘seismic sound barrier’, becoming an extremely fast earthquake.
Only a handful of such earthquakes have been recorded globally.
The authors believe that the first stage of rupture is crucial in causing the second stage to slide rapidly.
“While scientists discover that such reverse fault mechanisms could occur from theoretical models, our new study provides some clear evidence,” said Dr. Hicks. Most for this mysterious mechanism happens in a real error.
“Although the fault structure looks simple, how the earthquake evolved, and this is quite the opposite of how we predicted the earthquake before we started analyzing the data.”
“However, if similar types of boomerang earthquakes or similar boomerangs can occur on land, then a seismic fracture in the opposite direction in the middle of an earthquake could affect,” said the scientists. significantly affects the amount of ground shake caused ”.
“Due to the lack of previously observed evidence, this mechanism is not used in modeling earthquake scenarios and assessing risks from such earthquakes.”
“Boomerang earthquake detail tracking could allow us to find similar patterns in other earthquakes and add new scenarios to their models and improve earthquake impact prediction. . “
The findings have been published in the journal Natural geoscience.
SP Hicks et al. Back-propagated ultrasonic rupture during 2016 Mw 7.1 Romanche Variable fault earthquake. Nat. Geosci, published online August 10, 2020; wait: 10.1038 / s41561-020-0619-9