[CIG-SHORT] Benchmark Pylith with viscoelastic analytic solution for a pressurized sphere

[Charles Williams]

Hi Francisco,

Does the analytical solution include the initial elastic solution, and are you also using this in PyLith (I believe it is the default)?  Another possible issue is to make sure that your definition of viscosity is the same for the analytical and numerical solutions.  There is a factor of two that sometimes appears (look at the viscosity definitions in the PyLith manual and Paul’s book).

Cheers,
Charles

p.s.  Also, what are the dimensions of the cavity compared to the depth?  If this ratio is large, you will probably need a very refined mesh to accurately capture the solution.


> On 27/09/2016, at 9:52 AM, Francisco Delgado <fjd49 at cornell.edu> wrote:
> 
> Dear Pylith developers,
> 
> I'm trying to simulate the ground displacement produced by a small pressurised cavity surrounded by a viscoelastic shell (equation 7.105 from Segall's Earthquake and Volcano Deformation book) and Pylith does a good job within a few mm of uncertainty. The difference between the analytic and the numerical solution is at most 0.6 mm for a signal with a maximum amplitude of 2.49 cm, however I've noticed that this last figure increases as time goes forward, very small but in the end negligible variations (evident in the attached plot, the profiles are calculated for the point of maximum uplift).
> 
> <sphere_visco.png>. Is this a typical issue of numerical viscoelastic models or is it related to the relatively low resolution of the finite element mesh?? 
> 
> Thanks 
> 
> -- 
> --------------------------------------------------------
> Francisco Delgado
> PhD student in Geological Sciences
> Cornell University
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Charles A. Williams
Scientist
GNS Science
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