Unlocking Earthquake Secrets: Discovering the Hidden Mechanism Behind Earthquake ‘Ignition’

Recent research shows that a slow and steady movement might be a warning sign for earthquakes. This study looked at how materials break, specifically focusing on cracks in sheets of plastic.

The findings relate to real earthquakes, according to Jay Fineberg, a physicist at The Hebrew University of Jerusalem. He explained that the type of material doesn’t matter; the same physical processes occur whether we’re talking about plastic in a lab or tectonic plates under the Earth’s surface.

Earthquakes happen when tectonic plates get stuck and stress builds up. Fineberg points out that the plates are under pressure from forces trying to push them apart, but the brittle area between them doesn’t stretch. Eventually, this brittle section fails, causing an earthquake.

Interestingly, the process of fracture doesn’t happen all at once. First, a crack forms, and then it races across the interface, reaching speeds close to the speed of sound, which causes the ground to shake.

To understand how cracks form, Fineberg and his team combined math with lab experiments. They simulated earthquakes using blocks of polymethyl methacrylate, commonly known as plexiglass. They clamped these sheets together and applied a force, mimicking the conditions found at strike-slip faults, like California’s San Andreas Fault. Even though the materials differ, the mechanics of the fracture remain consistent.

Once a crack begins, it behaves like a line cutting through the material. Before a crack forms, however, a slow-moving phase called a nucleation front develops. Fineberg and his team discovered the nucleation front behaves differently than the quick crack that follows. They realized they needed to adjust their approach, modeling these fronts in two dimensions instead of one.

Picture a crack not as a simple line, but as a patch that starts where two plexiglass plates meet. The energy needed to break new material increases as the patch grows in size. For a while, this slow-motion patch won’t cause the rapid fractures that generate seismic waves. This early movement is “aseismic,” meaning it doesn’t release energy that would result in shaking.

However, the patch eventually expands beyond the brittle zone where the plates meet. When this happens, the energy balance shifts. There’s surplus energy that has to go somewhere, leading to a sudden explosive fracture.

The research, published in the journal Nature, sheds light on how slow movement can quickly turn into an earthquake. Fineberg suggests that if we could measure this aseismic activity on a fault line, we might be able to predict when an earthquake could occur. Although this is tricky in real-world scenarios, some faults experience long periods of slow movement without quakes.

Fineberg and his team are now working to identify signs of this transition from aseismic to seismic behavior in their laboratory models. They hope to uncover patterns that could provide insights into earthquakes, as they can observe and listen to the processes occurring in the lab in ways that are not possible in nature.