Microphysical Modeling of Carbonate Fault Friction at Slip Rates Spanning the Full Seismic Cycle

Area of Science:

• * Geophysics and rock mechanics
• * Fault gouge frictional behavior

Background:

• * Seismogenic rupture in carbonate faults is linked to friction changes with slip velocity.
• * Previous models explained low-velocity behavior but lacked high-velocity consensus.
• * The Chen-Niemeijer-Spiers (CNS) model previously addressed low-velocity frictional behavior.

Purpose of the Study:

• * To extend the Chen-Niemeijer-Spiers (CNS) model to high slip velocities (1 mm/s to 10 m/s).
• * To incorporate grain-scale deformation mechanisms activated by frictional heating.
• * To explain the transition in frictional behavior from low to seismic slip rates.

Main Methods:

• * Microphysically based modeling of carbonate fault gouges.
• * Inclusion of multiple grain-scale deformation mechanisms (plasticity, diffusion).
• * Simulation of localized shear bands with velocity-dependent grain size reduction.

Main Results:

• * The extended CNS model predicts a continuous transition in dominant deformation mechanisms with increasing velocity and temperature.
• * At low velocities, frictional granular flow with plasticity dominates.
• * At high velocities, grain boundary sliding with solid-state diffusion becomes significant.
• * Model results align with experimental data for calcite-rich rocks without invoking thermal decomposition or fluid pressurization.
• * The model captures steady-state and transient frictional aspects.

Conclusions:

• * The extended CNS model successfully explains carbonate fault friction across the full spectrum of slip velocities.
• * The model provides a physically based framework for understanding earthquake nucleation and seismic slip.
• * It offers a potential improvement for extrapolating laboratory friction data to natural fault conditions.