Dear Pylith team,
I have some questions. I am sorry if this is a basic question. I would like to ask why there are changes in a defined power-law parameter when calculating effective viscosity with PowerLawPlaneStrain viscoelastic materials in a 2D model. Laboratory experiments suggest a power-law rheology: η=Cσ^(1-n) or ε ̇=σ^n/2C, where σ is differential stress, n is the power-law exponent, C is the power-law parameter associated with temperature and rock composition (C=e^((Q/RT) )/2A), and ε ̇ is strain rate. If Q, R, T, and A are constants, C is a constant, is this correct?
I calculate the effective viscosity in postseismic periods as follows: (1) I have preseismic strain rate ε ̇_pre, viscosity η_pre, and power-law-exponent n. I determine the preseismic differential stress by σ_pre=2η_pre ε ̇_pre. (2) I solve for C_pre by using C_pre=η_pre σ_pre^(n-1). Then, I calculate A_T by A_T=√3^(n+1)/4C. Using an assumed reference-strain-rate e ̇ (10-16 s-1), I calculate reference-stress S_0 by S_0=(e ̇/A_T )^(1/n). By now, I have specified the three parameters for the PowerLawPlaneStrain viscoelastic material. (3) I obtain stress and total_strain after an earthquake from the Pylith modeling results. Now, the problem comes.
I use the inferred stress and total_strain to calculate C_post by C_post=σ_post^n/2ε ̇_post, where σ_post=|σ_xx-σ_yy | and ε ̇_post= ε/dt. But I find C_post is unequal to C_pre. I am very confused about this, why does C change? Isn’t it a constant?
Thank you in advance.