Scientists have tracked a boomerang earthquake in the ocean for the first time, providing clues as to how they could cause destruction on land. The researchers also managed to restore the image of the destruction zone. The team, led by scientists from the University of Southampton and Imperial College London, today reports its findings in the journal Nature Geoscience.
Tectonic earthquakes occur when rock plates are displaced or as a result of collisions between oceanic and continental platforms. In such collisions, mountains or depressions are formed and surface vibrations occur. During strong earthquakes, rock collapse can propagate along the entire fault line. Now an international team of researchers has recorded a boomerang-type earthquake, in which the rupture first spreads away from the original rupture, but then turns and moves in the opposite direction at a greater speed.
The strength and duration of a rupture along a fault affects ground shaking at the surface, which can damage buildings or cause a tsunami. Ultimately, knowledge of fault fracture mechanisms and related physics will help researchers create more accurate models and predictions of future earthquakes, and can also be used in earthquake early warning systems.
Although strong earthquakes (magnitude 7 or greater) occur on land and are measured by a nearby network of monitors (seismometers), these earthquakes often cause movement along a complex network of faults, such as dominoes. This makes it difficult to track the mechanisms underlying the origin of the seismic shear.
In 2016, they recorded a 7.1 magnitude earthquake along the Romansh fault zone and tracked the fracture along the fault. This showed that initially the rupture was moving in one direction and then reversed halfway through the earthquake and broke the “seismic sound barrier”, turning into an ultra-fast earthquake.
There are only a few such earthquakes registered in the world. The team believes that the first phase of the rupture was critical in generating the second, rapidly decaying phase.