Dynamic weakening during earthquakes controlled by fluid thermodynamics

Area of Science:

• Geophysics
• Rock Mechanics
• Earthquake Science

Background:

• Earthquakes are caused by fault weakening during slip.
• Dry faults weaken via frictional heating (flash heating).
• Fluid-rich faults are theoretically predicted to weaken by thermal pressurization.

Purpose of the Study:

• To experimentally investigate rock/fluid interactions during dynamic rupture.
• To determine how fluid thermodynamic properties influence fault weakening mechanisms.
• To understand the interplay between flash heating and thermal pressurization under varying fluid pressures.

Main Methods:

• Dynamic laboratory earthquake rupture experiments.
• Recording rock friction and slip under controlled stress and fluid pressure.
• Analysis of frictional heat generation and fluid pressure evolution.

Main Results:

• Flash heating drives fault weakening under dry and low fluid pressure (1 MPa).
• At high fluid pressure (25 MPa), flash heating is suppressed due to heat buffering by water's liquid-supercritical phase transition.
• Thermal pressurization becomes more dominant in inhibiting flash heating at elevated fluid pressures.

Conclusions:

• Fault weakening mechanisms are critically dependent on fluid thermodynamic properties and pressure.
• The heat buffering effect is most efficient at mid-crustal depths (2-5 km), relevant to anthropogenic earthquake nucleation.
• These findings refine our understanding of earthquake rupture dynamics and the role of fluids in fault mechanics.