# Patchiness in initial composition from GWB in spherical shell

**URL:** <https://community.geodynamics.org/t/patchiness-in-initial-composition-from-gwb-in-spherical-shell/2748>\
**Category:** ASPECT\
**Created:** [January 3, 2023, 4:55am UTC](https://community.geodynamics.org/t/patchiness-in-initial-composition-from-gwb-in-spherical-shell/2748 "2023-01-03T04:55:33Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![Mainak](https://avatars.discourse-cdn.com/v4/letter/m/b77776/32.png) [@Mainak](https://community.geodynamics.org/u/Mainak)\
**Post date:** [January 3, 2023, 4:55am UTC](https://community.geodynamics.org/t/patchiness-in-initial-composition-from-gwb-in-spherical-shell/2748/1 "2023-01-03T04:55:33Z")

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I am trying to use GWB to create initial conditions in a spherical shell geometry. When visualizing in GWB it is ok, but some patchy behavior is observed at the surface for the compositions of ASPECT output.

This is from visualization

 ![Screenshot from 2023-01-03 10-03-11](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/2X/e/e471475baadece603d323075c16e45c6d59ebc65.png)

This is from the output

 ![Screenshot from 2023-01-03 10-08-05](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/2X/8/8c8117ae91aeb40adb7e6bef0bb78428b7ac8825.jpeg)

I ran this model in debug mode. For mesh generation this was the script

```auto
subsection Mesh refinement
  set Initial global refinement = 3
  set Initial adaptive refinement = 3
  set Time steps between mesh refinement = 5
  set Strategy = temperature, composition, topography
  set Refinement criteria merge operation = plus
end

```

Increasing or decreasing the refinement level only affects the resolution of the patches but they remain regardless. What can be done for this?

Thanks,  
Mainak

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**Author:** ![mibillen](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/mibillen/32/169_2.png) [@mibillen](https://community.geodynamics.org/u/mibillen)\
**Post date:** [January 4, 2023, 5:43pm UTC](https://community.geodynamics.org/t/patchiness-in-initial-composition-from-gwb-in-spherical-shell/2748/2 "2023-01-04T17:43:22Z")

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Hello Mainak,

Do you set the parameter “min depth” for this region? In spherical geometry it might be necessary to set the min depth to a negative value so the region that is “inside” the region does not just miss the nodes at the surface. Try setting “min depth”:-10e3, like in this example:

“composition models”:[  
{“model”:“uniform”, “compositions”:[0], "min depth”:-10e3, “max depth”:10e3}]},

Magali

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<div class="post-metadata">

**Author:** ![Mainak](https://avatars.discourse-cdn.com/v4/letter/m/b77776/32.png) [@Mainak](https://community.geodynamics.org/u/Mainak)\
**Post date:** [January 5, 2023, 1:01pm UTC](https://community.geodynamics.org/t/patchiness-in-initial-composition-from-gwb-in-spherical-shell/2748/3 "2023-01-05T13:01:12Z")

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Hi Magali,

Many thanks for the suggestion, it has worked. When declaring the “min depth” it had to be done both in general description as well as in “composition models” then it worked. Like this

```auto
   {"model":"continental plate", "name":"continental plate", "min depth":-15e3,
     "composition models":[{"model":"uniform","compositions":[0], "min depth":-15e3}]}

```

Thank you!

Mainak

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<div class="post-metadata">

**Author:** ![mibillen](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/mibillen/32/169_2.png) [@mibillen](https://community.geodynamics.org/u/mibillen)\
**Post date:** [January 5, 2023, 9:31pm UTC](https://community.geodynamics.org/t/patchiness-in-initial-composition-from-gwb-in-spherical-shell/2748/4 "2023-01-05T21:31:28Z")

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So happy to hear that its fixed!  
Cheers,  
Magali