[CIG-SHORT] CIG-SHORT Digest, Vol 53, Issue 2

[Surendra Nadh Somala]

On Jan 26, 2011, at 8:02 AM, cig-short-request at geodynamics.org wrote:

> I am struggling in a very simple 2D simulation SCEC-TPV11 simulation.
> A 50m spacial resolution on fault meshing works fine, but when i try
> to use a mesh with 25m resolution on fault, I don't get a proper
> initiation as nodes outside the nucleation patch start to move (see
> joined figure). Lowering up to 1e-5s time step didn't work, I also
> increased the maximum iterations with still no success, I wish to know
> if I am overlooking important parameters or should i continue to
> increase the pre-conditioners till I get my result? I put the setup
> files in
> ftp://ftp-lgit.obs.ujf-grenoble.fr/pub/lgit/moussatn/

Changing the maximum number of iterations of pre-conditioners will not  
make any difference for the TPV11 because you are using ExplicitLumped  
solver.

Your friction.spatialdb file has 3 entries but you are use num-locs =2!

It doesn't appear to me that your initial tractions are set properly.   
I made this simple Matlab script (please see attached ) to set  
tractions, when I was working on TPV10.  Changing the static friction  
coefficient in my script could give you initial tractions for TPV11.   
You are using the same locations but there is a mismatch in values.   
This might have been the issue in your case although I am not sure how  
50m resolution worked.

Any chance you were plotting slip-rate instead of slip for the blue  
curve?

> On another matter, I don't understand in the manual how the file
> mat_prop.spatial.db can specify 2 different material properties for a
> volume on one side of the fault. Do I need to introduce 3 bodies
> instead, with 2 contact interface with cohesive cells? (one stick-slip
> for the fault and one stick for the heterogeneity)

You don't require a third body.  For a bi-material problem, you will  
have two entries in mat_props.spatialdb; one for the upper material  
and one for lower.  For instance if you have a 3D problem in a 45km x  
30 km x 15 km box with -15 <=z<=0 and there is a change of material  
properties at depth of 7.5km, you can use

0	0	-7.4		rho1	vs1		vp1
0	0	-7.6		rho2	vs2		vp2

The above settings should work well with 100m resolution.  For more  
finer resolution you can adjust z-coordinates accordingly.  Make sure  
data_dim=1 in the spatialdb file and num-locs=2.  You can double-check  
whether you are setting the parameters as required by opening the  
info.vtk file paraview.  I am positive that this should work.  If not,  
try two more values one each for upper and lower material by adding an  
entry at z=0 and z = -15km and change num-locs accordingly.

--Surendra

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