Mechanical behaviour of fluid-lubricated faults

Area of Science:

• Geophysics
• Rock Mechanics
• Tribology

Background:

• Fluids are common in Earth's fault zones, but their influence on fault mechanics is largely theoretical.
• Previous research has primarily relied on theoretical models to understand fluid viscosity effects on faults.

Purpose of the Study:

• To experimentally investigate the effect of fluid viscosity on the frictional properties of rocks.
• To determine how varying fluid viscosities influence static and dynamic friction coefficients during fault slip.

Main Methods:

• Conducted friction experiments on silicate and carbonate rocks under varying normal effective stresses (up to 20 MPa).
• Tested a range of slip rates (10 μm/s to 1 m/s) with four different fluid viscosities.
• Analyzed friction data in relation to the dimensionless Sommerfeld number (S) and elastohydrodynamic-lubrication (EHD) theory.

Main Results:

• Both static and dynamic friction coefficients decreased as fluid viscosity increased.
• Dynamic friction showed a dependence on the Sommerfeld number (S), aligning with EHD predictions.
• Slip weakening distance (Dc) increased significantly with viscosity at seismic slip rates.

Conclusions:

• Elastohydrodynamic-lubrication (EHD) can act as a weakening mechanism in fault zones under specific conditions.
• Fluid viscosity plays a critical role in determining fault behavior, potentially favoring slow-slip events for certain viscosity ranges at seismic slip rates.