The slip-rate, state-, temperature-, and normal-stress-dependence of fault friction.
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| Title: | The slip-rate, state-, temperature-, and normal-stress-dependence of fault friction. |
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| Authors: | Barbot, Sylvain1 sbarbot@usc.edu |
| Source: | Earthquake Science. Aug2025, Vol. 38 Issue 4, p304-338. 35p. |
| Subject Terms: | *Temperature effect, *Earthquakes, *Shear strength, *Strains & stresses (Mechanics), *Slow earthquakes, *Velocity, *Rock deformation |
| Abstract: | The mechanics of slow-slip events and earthquakes is controlled by the constitutive behavior of rocks in active fault zones, which is sensitive to many factors encompassing lithology, temperature, confining and pore-fluid pressure, and slip-rate, among others. Understanding the frictional properties of faults is crucial to predicting many aspects of the seismic cycle, from the source characteristics and recurrence patterns of earthquakes to the mechanics of remote triggering. Here, we describe a constitutive model that explains the slip-rate-, state-, temperature-, and normal-stress-dependence of fault friction for a wide variety of rock types, explaining the evolution of frictional stability under various barometric and hydrothermal conditions relevant to natural and induced seismicity, encompassing the brittle-ductile transition. The frictional strength is controlled by the area of contact junctions that form along a rough interface or by grain-to-grain contact in fault gouge and follows a nonlinear function of normal stress. The physical model explains the direct and evolutionary effects following perturbations in temperature, normal stress, and slip-rate, and the dependence of the frictional parameters on ambient physical conditions. The competition among healing and deformation mechanisms explains the dependence of fault stability on temperature, slip-rate, and effective normal stress for a wide range of rocks. The brittle-to-flow transition at the bottom of the seismogenic zone is caused by the thermobaric activation of semi-brittle deformation mechanisms. The model unifies and extends previous formulations, providing a single framework to explain rock deformation in Earth’s brittle and ductile layers. Understanding the mechanics of faulting is crucial for the prediction of natural and induced earthquakes. However, rock failure depends critically on many physical factors and remains elusive. Although laboratory experiments describe the temperature, pore-fluid and confining pressure, and composition controls on frictional strength, a physical model explaining these effects from first principles is still missing. Here, we present a constitutive law that captures the slip-rate-, state-, temperature-, and normal-stress-dependence of frictional strength applicable to rock types from various tectonic settings. The frictional resistance is proportional to the real area of contact at the interface. The seismic cycle is enabled by the competition between healing and contact rejuvenation that modulates the size and number of contact junctions. The resulting friction coefficient retains a sensitivity to normal stress, even at steady state. The model accurately predicts the direct and transient effects of temperature, slip-rate, and normal stress perturbations. Frictional instabilities can occur due to velocity-weakening or temperature-softening behavior. Invoking the competition of multiple healing and deformation mechanisms explains the slip-rate, temperature, and effective normal stress range of unstable behavior based on rock type. The brittle-ductile transition, associated with the thermal activation of a rate-dependent deformation process, is favored by low slip-rates, high temperatures, and high effective normal stress. Although the physical model incorporates many controlling factors, the effects of pore-fluid pressure, fluid chemistry, and mineral composition remain poorly understood. [ABSTRACT FROM AUTHOR] |
| Database: | Energy & Power Source |
| Abstract: | The mechanics of slow-slip events and earthquakes is controlled by the constitutive behavior of rocks in active fault zones, which is sensitive to many factors encompassing lithology, temperature, confining and pore-fluid pressure, and slip-rate, among others. Understanding the frictional properties of faults is crucial to predicting many aspects of the seismic cycle, from the source characteristics and recurrence patterns of earthquakes to the mechanics of remote triggering. Here, we describe a constitutive model that explains the slip-rate-, state-, temperature-, and normal-stress-dependence of fault friction for a wide variety of rock types, explaining the evolution of frictional stability under various barometric and hydrothermal conditions relevant to natural and induced seismicity, encompassing the brittle-ductile transition. The frictional strength is controlled by the area of contact junctions that form along a rough interface or by grain-to-grain contact in fault gouge and follows a nonlinear function of normal stress. The physical model explains the direct and evolutionary effects following perturbations in temperature, normal stress, and slip-rate, and the dependence of the frictional parameters on ambient physical conditions. The competition among healing and deformation mechanisms explains the dependence of fault stability on temperature, slip-rate, and effective normal stress for a wide range of rocks. The brittle-to-flow transition at the bottom of the seismogenic zone is caused by the thermobaric activation of semi-brittle deformation mechanisms. The model unifies and extends previous formulations, providing a single framework to explain rock deformation in Earth’s brittle and ductile layers. Understanding the mechanics of faulting is crucial for the prediction of natural and induced earthquakes. However, rock failure depends critically on many physical factors and remains elusive. Although laboratory experiments describe the temperature, pore-fluid and confining pressure, and composition controls on frictional strength, a physical model explaining these effects from first principles is still missing. Here, we present a constitutive law that captures the slip-rate-, state-, temperature-, and normal-stress-dependence of frictional strength applicable to rock types from various tectonic settings. The frictional resistance is proportional to the real area of contact at the interface. The seismic cycle is enabled by the competition between healing and contact rejuvenation that modulates the size and number of contact junctions. The resulting friction coefficient retains a sensitivity to normal stress, even at steady state. The model accurately predicts the direct and transient effects of temperature, slip-rate, and normal stress perturbations. Frictional instabilities can occur due to velocity-weakening or temperature-softening behavior. Invoking the competition of multiple healing and deformation mechanisms explains the slip-rate, temperature, and effective normal stress range of unstable behavior based on rock type. The brittle-ductile transition, associated with the thermal activation of a rate-dependent deformation process, is favored by low slip-rates, high temperatures, and high effective normal stress. Although the physical model incorporates many controlling factors, the effects of pore-fluid pressure, fluid chemistry, and mineral composition remain poorly understood. [ABSTRACT FROM AUTHOR] |
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| ISSN: | 16744519 |
| DOI: | 10.1016/j.eqs.2025.03.005 |
