Avalanches in granular faults can store more energy instead of releasing it.

Granular materials, like crushed rock in an earthquake fault, build up energy and swell before sudden slips called avalanches usually dump that energy and pack the grains tighter. Researchers tested a compressed granular faultgranular faultA layer of small solid particles, like sand, that is being pushed and can slip like a fault in the earth. to see if slips always relax this tension. They tracked twisting force, thickness, sound waves, and patterns of internal force. They discovered all four possible combinations of energy gain or loss paired with swelling or shrinking. Remarkably, some avalanches actually expand the layer and increase the stored elastic energy sent to the boundary. These slips shift lines of force outside the main sliding zone and make distinct sound signatures. Slips do not always relax disordered materials; they can push stress into an even more heavily loaded state.

Why it matters

This matters because it challenges a basic assumption about how faults behave. If avalanches can increase stored energy, then the buildup to a major slip might be more complex than previously thought. The finding has implications for understanding both lab experiments and real earthquakes.

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