20.02.12 - Scientists have succeeded in modelling what happens when two bodies slide against each other and thereby release the pressure; a discovery that has implications for the understanding of the magnitude of earthquakes.

David Kammer, a doctoral student at EPFL’s Computational Solid Mechanics Laboratory (LSMS), has developed a digital model that explains what happens at the interface between two materials when they slide against each other; like a book on a table, rubber soles on linoleum, or – more to the point – tectonic plates.

Earthquakes occur at the point where two tectonic plates meet. Between each period of sliding, forces accumulate between them up to the point where the friction resistance is overcome, leading to movement. This displacement of the Earth’s crust triggers a shock-wave that is transmitted to the surface of the planet. The scientists interviewed by Live Science put the physics of earthquakes in the “top ten” of the most interesting scientific mysteries.

Accumulation of energy determines the stick-slip
When two materials slide against each other, they don’t always react in the same way, according to the prevailing conditions, such as rigidity or the speed of movement. Sometimes the sliding is regular and homogenous; in the case of tectonic plates, the movement is hardly felt, or not at all. At other times, there is a succession of phases of stopping or speeding up, called “stick-slip”. Earthquakes are the result of sudden movement.

These heterogenous movements systematically trigger a shock-wave at the surface. But what determines the intensity? And why do some earthquakes create such devastation? David Kammer began by basing his research on experimental results obtained by external laboratories. “I wanted to understand the dynamics of the point at which the plates suddenly begin to slide against each other – in particular, the way it starts and is subsequently transmitted between the two solid bodies in contact. I discovered that the accumulation of energy at the breaking-point of the interface determines the acceleration of the sliding.”

The doctoral student, whose research results are being published in the journal Tribology Letters, has thus discovered another path to explore for the communities of mechanics and geoscience, by revealing that the energy-related aspects are critical.

"This research is supported by the European Research Council (ERC-StG UFO-240332) "