A team of researchers from the University of Amsterdam recreated earthquakes and landslides in the lab to help study these events, according to a study published in Science Advances. Using a miniature version of the ground, the team showed how these events are triggered by a small external shock wave that briefly turns the ground into a liquid.
The ground is not a true solid. It’s made up of granules, such as sand or rock. The same is true for the fault lines where two tectonic plates meet. This type of material is never fully stable and, when moving, it can have catastrophic effects for us on the surface. The problem is that researchers cannot predict or control when friction forces are no longer enough to stop an earthquake or a landslide.
To cover this knowledge gap, a team of physicists from the University of Amsterdam used a 1mm thick layer of tiny spheres to mimic the ground. This way, they could measure the response to external forces, similar to what happens on a mountain slope or a tectonic fault. They pressed a disc on the surface, which was slowly rotating at a constant speed. Bouncing a small ball next to this setup was enough to trigger a seismic wave, causing a miniature earthquake. “We found that a very small perturbation, a small seismic wave, is capable of causing a granular material to completely restructure itself,” explained Farain. For a brief moment, the granules behave more like a liquid rather than a solid. Once the wave is gone, stability returns but in a new configuration.
The authors suggest that the same happens in real seismic events. “Earthquakes and tectonic phenomena follow scale-invariant laws, so findings from our laboratory-scale frictional setup are relevant for understanding remote earthquake triggering by seismic waves in much larger-scale faults in the Earth’s crust,” said Farain.
Curiously, much of this work was “inspired” by lab conditions. “Initially, my experimental setup was just on a regular table, lacking all the fancy vibration isolation needed for precise measurements. Soon enough, I realised that simple things like someone walking by or the door closing could affect the experiment. I must have been a bit of a bother to my colleagues, always asking for quieter footsteps or gentler door closures.,” joked Farain.
Farain K and Bonn D. Perturbation-induced granular fluidization as a model for remote earthquake triggering.Sci. Adv.10,eadi7302(2024).DOI:10.1126/sciadv.adi7302