Effective normal stress and a Coulomb slip threshold
In a compression-positive Coulomb model for a closed fault, effective normal traction is σ′_n=σ_n−p.
Key knowledge
In a compression-positive Coulomb model for a closed fault, effective normal traction is σ′_n=σ_n−p. The shear-resistance magnitude is τ_r=c+μ_fσ′_n; the ideal slip threshold is |τ|=τ_r. Increasing fluid pressure at fixed total tractions lowers this modeled resistance. The threshold does not decide whether ensuing slip is seismic or stable.
Values and equations
σ′_n=σ_n−p; τ_r=c+μ_fσ′_n; |τ|=τ_r at the ideal threshold
- σ_n,σ′_n,p,τ,τ_r,c
- total/effective normal traction, fluid pressure, signed shear traction, resistance and cohesion Pa
- μ_f
- model friction coefficient 1
Conditions and scope
- σ′_n≥0, cohesion c≥0 and friction coefficient μ_f≥0, with parameters and stress convention stated. For a cohesionless frictional interface set c=0; strength for intact-rock fracture is a different calibrated model.
- Opening/tensile failure, changing normal stress, rate/state evolution and dynamic weakening need further laws. Pore-pressure changes can also change total stress; a pressure increase alone does not guarantee a rupture or determine its time.
Sources · 2
References
Sources retain their recorded scope. A source link alone does not establish verification of every statement.
- Induced Seismicity Potential in Energy Technologies, AppendixG, printed221–222, Coulomb Criterion and Effective StressNational Research Council — National Academies Press (2013)Reference guide
- PSG&T Chapter3, Role of Fluids and Effect of Pore Pressure on Failure, equation3.9Ben A. van der Pluijm and Stephen Marshak — University of MichiganReference guide
Evidence and review
Read actual AppendixG absolute-shear criterion, compression/effective-stress definition and stable-versus-seismic slip caveat, plus Michigan equation3.9 and its bounded empirical failure discussion. Renamed source fluid-pressureρ to p and defined positive compression. Excluded a universal friction coefficient, tensile continuation and the defective sign/parenthesis equation in the separate MIT problem set.
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Entry details
Permanent link to this entry ↗- Record identity
- uni-earth-fault-effective-friction
- Revision
- core.1
- Structured reference record
- University core expansion