It is well known that earthquakes and landslides are challenging to forecast and get ready for. However, scientists at the UvA Institute of Physics have shown how these events can be caused by a small external shock wave by studying a miniature version of the ground in the lab. It’s important to be prepared as it can lead to the ground briefly turning into a liquid!
The ground briefly turns into a liquid!
Unlike a true solid, the ground we stand on is generally made of granules such as sand grains or pieces of rock. Deeper down in Earth’s crust, the same holds for the fault lines where two tectonic plates meet. These types of disordered granular materials are never fully stable. And when they fail, it can have catastrophic effects for us, living on Earth’s surface.
The problem is: it’s not easy to predict or control when the friction forces resisting a landslide or earthquake will stop being enough to keep the ground in place. Thankfully, the physics works ex
Scientists at the University of Amsterdam, Kasra Farain and Daniel Bonn, have successfully recreated the forces of an earthquake in a lab setting using a 1-mm thick layer of tiny spheres. Each sphere is the same width as a human hair. By applying external forces to the granules and monitoring their response, the researchers were able to simulate the conditions present on a steep mountain slope or at a tectonic fault. This was achieved by pressing a disc on the surface and rotating it at a constant speed. They then observed the effects of a small seismic wave triggered by bouncing a ball next to the experimental setup.granules quickly moved in response: they had caused a small earthquake!” “We discovered that even a small disturbance, a tiny seismic wave, has the potential to completely reorganize a granular material,” Farain explains. Further investigation showed that for a brief period, the granules act like a liquid instead of a solid. Once the triggering wave passes, friction takes over again and the granules become jammed once more, but in a new arrangement. The same phenomenon occurs in actual seismic events. “Earthquakes and tectonic events adhere to scale-invariant laws, so the results from our laboratory-scale frictional setup are applicable to real-world scenarios.
“Understanding remote earthquake triggering by seismic waves in much larger-scale faults in the Earth’s crust is relevant,” says Farain.
The researchers have demonstrated that the mathematical model derived from their experiments effectively explains how the 1992 Landers earthquake in Southern California remotely triggered a second seismic event 415 km to the north. Furthermore, they have shown that their model accurately describes the increase in fluid pressure observed in the Nankai subduction zone near Japan following a series of small earthquakes in 2003.
Inspiration from an unstable table Interestingly, this entire research project was inspired by a wobbly table.Farain credits his colleagues for the success of his project, stating that his initial experimental setup was on a regular table without the necessary vibration isolation for accurate measurements. He soon realized that even simple movements, such as someone walking by or the door closing, could impact the experiment. He admits to being a bit of a nuisance to his colleagues, always asking for quieter footsteps and gentler door closures. Inspired by the disruptions caused by his colleagues’ movements, Farain delved into the physics at play. He eventually upgraded to a proper optical table for the setup, allowing for more stability and accurate results.I would often catch myself daydreaming about how I could disrupt the work of others by creating controlled disturbances. But, because of my mischievous nature, I didn’t stop there. Not long after, I decided to return to the lab with a loudspeaker to make some noise and observe the effects of these controlled disruptions!”
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