[CIG-SHORT] Stress issue with spherical model

[Demian Gomez]

Dear all,

I think I found the problem with the lithostatic stress in my spherical
model. I'm not sure if it's a bug or not. I am specifying the stress using
a SpatialGridDB in lat lon h, where I declare my coordinate system as:

  cs-data = geographic {
  to-meters = 1
  space-dim = 3
  ellipsoid = sphere
  datum-vert = ellipsoid
  is-geocentric = false
}

In pylithapp.cfg I declare my coordinate system as:

[pylithapp.mesh_generator.reader]
coordsys = spatialdata.geocoords.CSGeo
coordsys.ellipsoid = sphere
coordsys.datum_vert = ellipsoid
coordsys.is_geocentric = true

The problem seems to be that Pylith is still using an ellipsoid instead of
using ellipsoid = sphere for the SpatialGridDB (I think). I verified this
by doing the following two experiments (see attached PDF):

1) I've created the spatialdb by calculating the lithostatic stress on a
lat lon h grid.
2) Same as before but this time I added a stress "offset" of 10 m (offset =
10*g*rho). This is equivalent to radially scaling the spatialdb.

>From the attached figure, you'll notice that in experiment 1, the
displacements are 0 at the center of the domain (the picture shows the
domain cut by a plane). In experiment 2, which has the stress offset, the
center of the domain shows displacements pointing towards the geocenter
(stress defect) and a zero displacement ring around the center of the
domain. Moving away from this ring (towards the edge of the domain), there
is a region where the displacements point up, showing an excess of stress.
I've depicted each experiment schematically in the figure.

Would it be possible to verify if what I found is correct? Or maybe there's
something wrong with my configuration.

Thanks!
Demián

--
*Dr. Demián D. Gómez*
Postdoctoral Researcher
The Ohio State University - School of Earth Sciences
275 Mendenhall Laboratory
125 South Oval Mall
Columbus, Ohio 43210
Cell: +1 (901) 900-7324
email: gomez.124 at osu.edu
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