[CIG-SHORT] Pylith for Post Glacial Rebound

[Charles Williams]

Hi Francisco,

The reason that people usually use springs for this sort of thing (as far as I know) is because they are using the infinitesimal strain approximation.  With this sort of approximation, vertical motion doesn't change the gravitational load, which means that any vertical motion due to gravitational variations will continue indefinitely.  To compensate for this, people put springs at the boundaries of density contrasts, where the spring constants are proportional to the density contrast.  This is also an approximation, but I think it usually does a reasonable job if you don't have complex density variations.

Our approach with PyLith has been to use a true large deformation formulation, which should accomplish the same thing with more generality and greater accuracy.  To use this, you will have to switch the problem type, and you will need to use the nonlinear solver, since there is geometric nonlinearity.

I haven't read the paper you mention, so there may be something I'm missing.  Let us know if the reason for using springs is what I've described above.  If so, you should be able to use the large deformation formulation for your problem.

Cheers,
Charles


On 23/07/2013, at 7:37 AM, Francisco Delgado De La Puente wrote:

> Hi, I was one of the atendees to the Pylith course about one month ago and I'm planning to use it to model post glacial rebound. However, as the PGR equation of motion is different than the usually equation of motion implemented in finite element packages, the boundary conditions must be modified in such a way that elastic springs ( Winkler foundation) must be attached to the free surface and the elastic-viscoelastic interface (Wu, P. (2004), Using commercial finite element packages for the study of earth deformations, sea levels and the state of stress, Geophys. J. Int., 158, 401–408.) So my question is the following, are does boundary conditions implemented in Pylith?? I have looked in the manual but the only thingg I've found springs are the for the physical analogy of the Maxwell viscoelastic model.
> 
> Best regards 
> 
> -- 
> --------------------------------------------------------
> Francisco Delgado
> PhD student in Geophysics
> Cornell University
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Charles A. Williams
Scientist
GNS Science
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C.Williams at gns.cri.nz

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