The dependence of seismic fault friction on temperature is different than previously thought

For decades, earthquake researchers have believed that rock friction within fault lines follows a simple relationship with temperature.

However, a new study published in the Proceedings of the National Academy of Sciences led by the University of Southern California suggests otherwise. My findings reveal that different underlying mechanisms influence the frictional resistance of faults, posing a challenge to the common understanding of seismic activity among researchers.

“The classic view of fault friction has always been that fault friction evolves continuously with temperature,” said Sylvain Barbot, assistant professor of geosciences in the USC Dornsife College of Letters, Arts and Sciences. “But my study shows that the direct effect of friction is largely unrelated to temperature until the point where rocks transition from brittle to semi-brittle, where the effects of temperature change dramatically.”

A fragile transition

The research was conducted using data from experiments on different types of rocks, including granite, basalt and olivine, under conditions that mimic those found deep within the Earth. Barbot found that when rocks go from brittle to semi-brittle, a change occurs that is important for understanding rock mechanics and geology.

In the brittle state, rocks deform and decompose by cracking and cracking. In the semi-brittle state, rocks exhibit a combination of brittle and ductile deformation, the process in which rocks permanently change shape by “flowing” or “bending” under pressure.

Sylvain Barbot is an associate professor of geosciences at USC Dornsife. (USC Image/Stephen Gee)

“Contrary to traditional models of rock frictional behavior, I found that the direct effect of friction is not always related to temperature,” Barbeau said. Instead, there are abrupt changes in rock friction during the transition to quasi-brittle behavior. “This means we need to rethink the fundamental basis of fault mechanics used to predict the seismic activity of earthquakes.”

Reconsidering the behavior of earthquakes

In the context of rock friction studies, the direct effect of friction refers to the instantaneous change in friction in response to a sudden change in sliding speed when two solid surfaces move relative to each other along a fault or fracture.

Most theories of friction are based on the belief that the speed at which two surfaces move relative to each other depends continuously on temperature. Barbot's study challenges the previously assumed dependence of thermal activation, which will require rethinking predictive models of fault friction to accurately predict earthquakes.

The next step of this research is to improve understanding of fault friction. “When integrated into physics-based models of the seismic cycle, every improvement we discover has the potential to improve the accuracy and reliability of earthquake hazard assessments and long-range forecasts,” Barbot said.

About the Study: This research was supported by the National Science Foundation under Award Number EAR-1848192.

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