“Boomerang” earthquake, the killer earthquake that comes back to strike twice

Because some cities get hit twice in a matter of seconds

The secret to this deadly behavior lies in a complex dance of friction and pressure within the Earth’s crust. According to advanced simulations by researchers Yudong Sun and Camilla Cattania, when an earthquake runs in a single direction over large distances, it can trigger a back-propagation mechanism. The friction along the fault does not simply disappear, but undergoes sudden changes that act as a sort of “spring” ready to spring back. “The region behind the earthquake, which stops slipping, may rupture again because it has accumulated enough stress to slip again“, explains Cattania. This means that the foundations of buildings, already compromised by the first pass, suffer a second amplified attack just as the structure is trying to absorb the initial impact.

The invisible threat beneath our feet

The real danger lies in the subtle nature of these events: for those on the surface, distinguishing a boomerang earthquake from a common earthquake is almost impossible, since the shaking of the ground appears as a single, chaotic destructive event. However, Seismic data collected during the catastrophic Tohoku earthquakes in 2011 and the 2023 Turkey and Syria earthquakes suggest that this “rebound” is much more frequent than suspected. The MIT discovery now forces the international community to rewrite safety protocols: “mature” and straight faults, considered more predictable until now, actually hide the potential to generate double ruptures. Identifying these back-propagation fronts has become the new priority to mitigate risks and try to predict where and when the earth will decide to strike again.

Cover image: A secondary ‘boomerang’ rupture front propagates backwards. Courtesy of the researchers.