[aspect-devel] Continental extension model

[John Naliboff]

Hi Mohamed,

The value is indeed related to the fact that there is inflow at the 
base.  Many months ago, I was seeing odd behavior in the compositional 
fields and I suspected not having the mantle layer extend well past the 
model base might be one of the reasons.

However, at the moment I can't recall if this alone fixed the issue.  In 
theory, the simulation should work fine as long as the mantle layer is 
defined as extending exactly to the model base.

Aside, one way to improve the accuracy of the compositional field 
advection is by using the DG method option for the compositional 
discretization.  In the input file I sent you, add the following lines:
     subsection Discretization
       set Use discontinuous composition discretization = true
       subsection Stabilization parameters
           set Use limiter for discontinuous composition solution = true 
# apply the limiter to the DG solutions
           set Global composition maximum = 1.0, 1.0, 1.0, 1.0
           set Global composition minimum =  0.0, 0.0, 0.0, 0.0
       end
     end

To use this option you will need to work of the development version of 
both ASPECT and deal.ii.  Let us know if you have any issues getting 
things installed on this front or with using the DG method.  If you see 
anything odd in the models, please do not hesitate to email the list!

Last, I just opened a pull request for a cookbook related to this input 
file.  You can check out my forked copy ASPECT (branch 
continental_extension_cookbook) if you want to take a look at it before 
it gets merged.  Even better, make some comments on the pull request!

Cheers,
John

*************************************************
John Naliboff
Assistant Project Scientist, CIG
Earth & Planetary Sciences Dept., UC Davis

On 10/20/2016 08:02 AM, Mohamed Gouiza wrote:
>
> Hi John,
>
> In the continental extension input file that you sent me, the mantle 
> compositional field is defined as 70.e3 && y>*-100.e3*
>
> Is the -100.e3 a typo or is it because of the prescribed inflow at the 
> base of the model?
>
> Mohamed
>
> *From:*Aspect-devel [mailto:aspect-devel-bounces at geodynamics.org] *On 
> Behalf Of *John Naliboff
> *Sent:* 10 October 2016 17:12
> *To:* aspect-devel at geodynamics.org
> *Subject:* Re: [aspect-devel] Continental extension model
>
> Hi Mohamed,
>
> An example continental extension input file is attached, which will be 
> submitted as a cookbook example in the next few days.
>
> In this example, extension is driven by prescribed outflow on the 
> sides and inflow at the base.  The rheology is dislocation creep with 
> different flow laws for the upper/lower crust and mantle.  Internal 
> friction angle (20 degrees) (20 MPa) are within the range of commonly 
> used values.  No strain-weakening, but I have a pull request open that 
> implements this.
>
> Most extension problems include the asthenosphere, while this model 
> only goes down to 100 km.  As such, I would only use this type of 
> setup for studying early stage extension. Any problems examining 
> extension from start to breakup should extend to at least 150 km. In 
> this case, one might alter the simple boundary conditions I've prescribed.
>
> Hope this helps and let me know you if you have any questions about 
> the input file.
>
> Cheers,
> John
>
>
>
>
>
> *************************************************
> John Naliboff
> Assistant Project Scientist, CIG
> Earth & Planetary Sciences Dept., UC Davis
>
> On 10/10/2016 12:59 AM, Mohamed Gouiza wrote:
>
>     Hi John,
>
>     I looked for the continental extension model that you showed in
>     the online workshop last month, but couldn’t find it in tests/ folder.
>
>     I’ve been running several extension models with the visco-plastic
>     material model and I am interested in knowing the visco-plastic
>     law parameters that you used and how do you prescribe the boundary
>     conditions: is the extension rate defined the same way as in the
>     crustal deformation example in the cookbook by Cedric?
>
>     Thank you
>
>     -------------------------------------------------
>     Mohamed Gouiza, Research Fellow
>     Basin Structure Group, Institute of Applied Geosciences
>     University of Leeds, School of Earth and Environment
>
>     Leeds,  LS2 9JT, UK
>
>     M.Gouiza at leeds.ac.uk <mailto:M.Gouiza at leeds.ac.uk>
>     +44 7985 782073
>     -------------------------------------------------
>
>
>
>
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