Reconstructed image of the fracture zone. Credit: Hicks et al.
Scientists saw a ‘boomerang’ earthquake along the Atlantic fault line, which provided clues as to how they could cause destruction on land.
Earthquakes occur when rocks suddenly break on a fault – a boundary between two blocks or slabs. During large earthquakes, rock breaking can spread the fault line. Now, an international team of researchers has recorded a ‘boomerang’ earthquake, in which the rupture initially spreads from initial break, but then rotates and runs the other way back at higher velocities.
The strength and duration of fractures along a fault affect the subsoil of shaking soil on the surface, which can cause damage to buildings or tsunamis. Finally, knowing the mechanisms of how errors break and the physics involved will help researchers make better models and predictions of future earthquakes, and be able to inform earthquake systems for earthquakes.
The team, led by scientists from the University of Southampton and Imperial College London, reported their results in Nature Geoscience is a monthly scientific journal published by the Nature Publishing Group that covers all aspects of Earth Sciences, including theoretical research, modeling, and fieldwork. Other related work is also published in fields that include science, geology, geophysics, climatology, oceanography, paleontology, and space science. It was founded in January 2008.
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Break the seismic sound barrier
While large (magnitude 7 or higher) earthquakes occur on land and are measured by nearby networks of monitors (seismometers), these earthquakes often trigger movement over complex networks of faults, such as a series of dominoes. This makes it difficult to follow the underlying mechanisms of how this ‘seismic slip’ occurs.
Under the ocean, many types of faults have simple shapes, so you get the option under the bonnet of the ‘earthquake engine’. However, they are far from large networks of seismometers on land. The team used a new network of underwater seismometers to control the Frache zone of the Romanche, a fault line that stretches 900 km below the Atlantic Ocean near the equator.
In 2016, they recorded a magnitude 7.1 earthquake along the Romanesque fracture zone and followed the fault at the fault. This showed that the eruption initially traveled in one direction before half-reversing the earthquake and breaking the ‘seismic sound barrier’, and became an ultra-rapid earthquake.
Only a handful of such earthquakes have been recorded worldwide. The team believes that the first phase of the fracture was crucial in causing the second, rapid slip phase.
Feeding earthquake predictions
First author of the study Dr. Stephen Hicks, of the Department of Earth Sciences and Engineering at Imperial, said: “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 found in a real debt occurs.
“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.”
However, the team says that if similar types of reversible or boomerang earthquakes can occur on land, a seismic rupture that rotates halfway through an earthquake could dramatically affect the amount of ground caused.
Given the lack of observational evidence for now, this mechanism has not been responsible in modeling earthquake scenarios and assessing the dangers of such earthquakes. The detailed monitoring of the boomerang earthquake could allow researchers to find similar patterns in other earthquakes and add new scenarios to their modeling and improved earthquake forecasts.
The ocean seismometer network used part of the PI-LAB and EUROLAB projects, a multi-million dollar experiment funded by the UK Environmental Research Council, the European Research Council, and the National Science Foundation in the FS.
Reference: “Back-propagating rupture of supershear in the 2016 Mw 7.1 Novel Transforms Earthquake of Guilt ”by Stephen P. Hicks, Ryo Okuwaki, Andreas Steinberg, Catherine A. Rychert, Nicholas Harmon, Rachel E. Abercrombie, Petros Bogiatzis, David Schlaphorst, Jiri Zahradnik, J-Michael Kendall, Yuji Yagi, Kousuke Shimizu and Henriette Sudhaus, August 10, 2020, Nature Geoscience.
DOI: 10.1038 / s41561-020-0619-9
