[aspect-devel] internal velocity boundary conditions

Jonathan Perry-Houts jperryh2 at uoregon.edu
Tue May 12 17:49:53 PDT 2015

I actually had this on my list of hackathon items as well. It would be
very useful.

On 05/12/2015 05:46 PM, Thorsten Becker wrote:
> Likewise not at the hackathon myself, but this exact application (for
> the Tohoku setting) would be of great interest to my group as well...
> Thanks!
> Thorsten W Becker
> geodynamics.usc.edu <http://geodynamics.usc.edu/~becker>
> On Tue, May 12, 2015 at 5:43 PM, Magali Billen <mibillen at ucdavis.edu
> <mailto:mibillen at ucdavis.edu>> wrote:
>     Hello Everyone,
>     Unfortunately I’m not going to make it to Hackathon to ask this
>     question in person, but this way everyone
>     can read (ignore?) and hear or contribute to the response.
>     The short form of my question is: Is it possible to define
>     “internal” velocity boundary conditions in Aspect: that is
>     can I fix the velocity at nodes inside the model domain? If the
>     answer is yes, can someone comment on the basic steps 
>     that would be needed (e.g., need to flag these nodes as “boundary
>     conditions” so they get handled properly during assembly of the
>     solution matrices, then assign velocities,…). 
>     Here is the background for why I ask this question:
>     One of the projects we are starting to develop in Aspect in my group
>     is instantaneous models for a specific 
>     subduction zones. The key issue with these models is that we need to
>     define a starting thermal structure
>     that is based on the observed geometry of the subducted plate (e.g.,
>     from seismicity). There are different
>     was to do this, and I’ve done several of them for previous models
>     completed using Citcom. 
>     Based on that experience, and given the AMR capabilities of Aspect,
>     I think the best (most accurate and easiest) way to
>     define the starting thermal structure is to run model in which you
>     have defined the surface of the plate
>     INSIDE the model (going down into the mantle) and then define fixed
>     velocities associated with this surface.
>     Note it is not necessary for the elements to conform to this surface
>     (no distortion of the grid), we can use refinement of the grid to
>     get accurate enough for our purposes. 
>     Once the velocity conditions inside the mesh are defined together
>     with the normal external boundary conditions and an initial
>     temperature structure for the plates at the actual top of the mesh,
>     then we would run this model forward in time to kinematically
>     “subduct” the plate. This will allow us to create a smooth 3D
>     starting temperature models for our instantaneous dynamically-driven
>     models that follows the observed shape of the slab.
>     In addition to using this capability for the purpose describe above,
>     this would allow Aspect to also run what is commonly referred to as
>     “mantle wedge thermal models”, in which the subducted plate and
>     overriding plates are really used as boundary conditions on the
>     flow/temperature in the mantle between them. These models are
>     commonly used to look at the detailed thermal structure and melting
>     in the mantle wedge.
>     Cheers,
>     Magali
>     --------------------------------------------------
>     Professor of Geophysics & UCD Chancellor Fellow
>     Chair, Geology Graduate Program
>     Earth & Planetary Sciences Dept., UC Davis
>     Davis, CA 95616
>     2129 Earth & Physical Sciences Bldg.
>     Office Phone: (530) 752-4169 <tel:%28530%29%20752-4169>
>     http://mygeologypage.ucdavis.edu/billen/
>     --------------------------------------------------
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