In a significant advancement that could transform earthquake science, researchers from the University of Southern California (USC) have developed a groundbreaking laboratory earthquake model that links the real contact area between fault surfaces to the mechanics of earthquake occurrences. This pioneering study, published in the Proceedings of the National Academy of Sciences, offers a promising pathway toward earthquake prediction and early warning systems.
“We’ve essentially opened a window into the heart of earthquake mechanics,” said Sylvain Barbot, associate professor of earth sciences at the USC Dornsife College of Letters, Arts and Sciences and principal investigator of the study. “By watching how the real contact area between fault surfaces evolves during the earthquake cycle, we can now explain both the slow buildup of stress in faults and the rapid rupture that follows. Down the road, this could lead to new approaches for monitoring and predicting earthquake nucleation at early stages.”
For decades, scientists have used empirical "rate-and-state" friction laws to model earthquake behavior — effective but limited mathematical constructs that lacked direct physical interpretation. This new research changes that paradigm by revealing that the so-called "state variable" central to these models corresponds to the real area of contact — tiny, isolated junctions where rough fault surfaces actually meet.
A Window Into Earthquake Dynamics
Using transparent acrylic materials and high-speed cameras, the USC research team captured earthquake ruptures in real time. LED light was passed through the materials to visually track the evolution of contact junctions during simulated quakes. These optical measurements revealed that approximately 30% of the contact area disappears in milliseconds during fast ruptures, leading to dramatic weakening and initiating an earthquake.
“We can literally watch the contact area evolve as ruptures propagate,” said Barbot. “This direct observation helps validate decades of theoretical modeling with actual, physical evidence.”
The discovery provides the first-ever physical interpretation of the mathematical state variable used in earthquake models since the 1970s, bridging the gap between theory and physical mechanism.
From Simulation To Prediction
By analyzing 26 simulated earthquake scenarios, the researchers demonstrated that rupture speed and fracture energy closely match predictions from linear elastic fracture mechanics. The computer models accurately mirrored both fast and slow laboratory earthquakes — including stress drops and even changes in light transmission during ruptures.
Since the real contact area influences key physical properties of faults — such as electrical conductivity, hydraulic permeability, and seismic wave transmission — the findings open the door to new monitoring techniques. These physical proxies could be used to observe changes in fault conditions over time, potentially providing early warning signals of an impending quake.
“If we can monitor these properties continuously on natural faults, we might detect the early stages of earthquake nucleation,” Barbot explained. “This could lead to new approaches for monitoring earthquake nucleation at early stages, well before seismic waves are radiated.”
Looking Ahead
The next phase of research involves scaling up this model beyond laboratory conditions to real-world fault zones. According to Barbot, the ultimate goal is to lay the foundation for a new generation of earthquake monitoring and early warning systems rooted in the physical evolution of fault surfaces.
“Imagine a future where we can detect subtle changes in fault conditions before an earthquake strikes,” Barbot said. “That’s the long-term potential of this work.
