[CIG-SHORT] Rate and State and Initial Traction

[Romain Jolivet]

Hello Brad, Matt, Charles and the pylith team,

Following your advice from the other day, I am experimenting  how to create earthquakes on a frictional interface by applying a traction change history. It works fine with the SlipWeakening law in 2D. I'm trying to move on to the RateStateAgeing behavior and I have problems applying the initial traction conditions:

I use a SimpleDB to apply the frictional properties on the fault: one domain is rate-strengthening, the other is rate-weakening with a linear transition between the two domains. If I do not try to turn on any traction_perturbation option, the code runs great, and I have a slow slip all the along the fault at any time. 

As I want the rate-weakening domain to be stuck sometimes, I want to turn on traction_perturbation.db_initial. I use a SimpleDB to put a negative traction all along the fault, and a shear traction compatible with the friction coefficients I impose. However, when I run this, I have the following error message from PETSc (I attach the log):

 >> /Users/jolivetinsar/MYBIN/pylith/pylith-1.7.1-darwin-10.6.8/lib/python2.7/site-packages/pylith/problems/Implicit.py:215:step
 -- implicit(info)
 -- Solving equations.
  0 SNES Function norm 2.679589636063e+01 
    0 KSP Residual norm 9.637565795900e-01 
    1 KSP Residual norm 3.564937135471e-08 
    2 KSP Residual norm 4.313963401911e-16 
    3 KSP Residual norm 3.050427683646e-16 
    4 KSP Residual norm 2.490663081181e-16 
    5 KSP Residual norm 2.156976950523e-16 
    6 KSP Residual norm 1.929258577738e-16 
    7 KSP Residual norm 1.761163907914e-16 
    8 KSP Residual norm 1.630520838230e-16 
    9 KSP Residual norm 1.525212509706e-16 
   10 KSP Residual norm 1.833325155789e-11 
   11 KSP Residual norm 7.039784754868e-23 
  Linear solve converged due to CONVERGED_ATOL iterations 11
[0]PETSC ERROR: --------------------- Error Message ------------------------------------
[0]PETSC ERROR: Floating point exception!
[0]PETSC ERROR: Infinite or not-a-number generated in norm!

If anyone has an idea about that error message....

I think it has to do with some slip vector. If I set friction.min_slip_rate=1e-1, this problem does not happen (the nonlinear solver does not converge, but at least, no crash). If I set the normal traction to be positive, it does not crash as well (and it does not converge as well). I join to this message the cfg file I am using for that experiment. 

Thank you
Romain
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Romain Jolivet
Postdoctoral Scholar
Geological and Planetary Sciences
California Institute of Technology, Pasadena, CA 
rjolivet at caltech.edu
+1 (626) 560 6356