[aspect-devel] internal velocity boundary conditions

Thorsten Becker twb at usc.edu
Tue May 12 17:46:48 PDT 2015

Likewise not at the hackathon myself, but this exact application (for the
Tohoku setting) would be of great interest to my group as well...


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> 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
> http://mygeologypage.ucdavis.edu/billen/
> --------------------------------------------------
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