[aspect-devel] Using seismic tomography as an input

Bremner,Paul M pbremner at ufl.edu
Fri Oct 20 06:52:15 PDT 2017 

Hi John, Phil,


Something I've had on my back burner is to add functionality to the S40RTS plug-in (maybe ascii too?) to optionally use the initial density distribution obtained when mapping the seismic velocities to temperature. But perhaps there is a different way of doing this, or maybe the density mapping wasn't used for a reason. Thoughts?


- Paul


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Today's Topics:

   1. Re: Using seismic tomography as an input (John Naliboff)
   2. Re: Using seismic tomography as an input (Bremner,Paul M)
   3. Re: Dynamic topography (Lev Karatun)


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Message: 1
Date: Thu, 19 Oct 2017 12:53:26 -0700
From: John Naliboff <jbnaliboff at ucdavis.edu>
To: aspect-devel at geodynamics.org
Subject: Re: [aspect-devel] Using seismic tomography as an input
Message-ID: <85b6b133-5ac6-36bb-f708-2ae5287c8934 at ucdavis.edu>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"

Hi Phil,

It certainly is possible. The plugin for S40RTS maps seismic velocity
variations to temperature, which are provided as the initial condition.
While it make sense to map S40RTS into a spherical coordinate system, it
is straightforward to map a seismic velocity model in cartesian
coordinates. One simply needs to specify how the geographic coordinates
map to a cartesian grid.

One can also read in the initial temperature field through the ascii
input option (e.g., velocity->temperature are done externally). The user
simply has to take into account the formatting requirements for each
coordinate system (specified in the documentation) when reading in the
ascii data. One can also specify the initial compositional field
structure via ascii text files. I've used this method for reading in
CRUST1.0 in various coordinate systems. So, lots of options!

If one of your colleagues has specific questions or needs to help
getting started, please have them contact us!

Cheers,
John

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

On 10/19/2017 12:37 PM, HERON, PHILIP J. wrote:
>
> Hi all,
>
>
> I've had a number of people asking me about using ASPECT with
> available seismic tomography data - to input seismic data and obtain
> density and possibly gravity models. I know this is possible for
> global spherical models (as shown the S20RTS), but is it possible for
> a 3D cartesian seismic input? Or would this require working on a plug in?
>
>
> Cheers,
>
>
> Phil
>
>
>
>
>
>
> _______________________________________________
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Message: 2
Date: Thu, 19 Oct 2017 21:04:30 +0000
From: "Bremner,Paul M" <pbremner at ufl.edu>
To: "aspect-devel at geodynamics.org" <aspect-devel at geodynamics.org>
Subject: Re: [aspect-devel] Using seismic tomography as an input
Message-ID:
        <BN6PR08MB26765B955B49910B06C98AB4CE420 at BN6PR08MB2676.namprd08.prod.outlook.com>

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Hi Phil,


I believe a 3D Cartesian model can be input into the ascii plug-in.


I also just want to make sure I understand your purpose correctly, are you hoping to input seismic tomography models for the express purpose of obtaining a density and gravity model? Or are you wanting to simply use the tomography models to feed a density model to ASPECT?


I believe that both the S40RTS and ascii plug-ins assign the temperature field in ASPECT, and not the density. For example, in S40RTS the velocity perturbation at a particular point is converted to density perturbation by multiplying a constant scale factor. That value is then multiplied by 1/alpha to get temperature perturbation, which is added to a background temperature for that point.

Cheers,
Paul
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Message: 3
Date: Thu, 19 Oct 2017 23:41:07 -0400
From: Lev Karatun <lev.karatun at gmail.com>
To: "aspect-devel at geodynamics.org" <aspect-devel at geodynamics.org>
Subject: Re: [aspect-devel] Dynamic topography
Message-ID:
        <CAPGyz25nfsEu1JPpYPhZjAqn2KiVBFQBppBjwzN=ff28O7D3VA at mail.gmail.com>
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Thank you everyone for the responses!

I kind of realized dynamic topography should be around zero when free
surface in enabled, but in reality in some of my models it was not
(reaching hundreds and even thousands of meters). I assume it means the
errors were high when the surface displacements were calculated? Should I
be worried about it? Is there a way to fight it? I tried decreasing the
free surface solver tolerance, but it didn't help.

Best regards,
Lev Karatun.

2017-10-19 15:23 GMT-04:00 Rene Gassmoeller <rene.gassmoeller at mailbox.org>:

> As Ian mentioned, unfortunately there is currently no option to do this.
>
> There is an open issue for this fact: https://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_geodynamics&d=DwIGaQ&c=pZJPUDQ3SB9JplYbifm4nt2lEVG5pWx2KikqINpWlZM&r=Wl19MSBMb4DZXdORUmp5jA&m=LL9fug0ZE7qJZzKQjUMkIsvL0aLvN-x7mpaYSYowf0A&s=5TaO9E57deZ5NcMMBpIje94EhzplkyR6wWQPaLXtzOE&e=
> /aspect/issues/1270, and it is on the list of things that 'should be
> done', but never get done, because there are always more important things
> to do. If anyone wants to go ahead with this issue, we would be grateful
> for it :-).
>
> Best,
>
> Rene
>
> On 10/19/2017 11:18 AM, Ian Rose wrote:
>
> A bit of context: I agree that the naming of the "topography" and "dynamic
> topography" postprocessors are a bit confusing (the distinction is
> described in the manual, section A.114). They are that way largely for
> historical reasons, as Jacky and I were working on those at roughly the
> same time and did not coordinate naming efforts. But yes, what Wolfgang and
> Timo say is correct: they are measuring different things. With a free
> surface, you expect the dynamic topgraphy to be near zero, since we are
> enforcing no-stress boundary conditions there!
>
> As to your other question, Lev: the "topography" postprocessor should
> provide an option to output the full topography, rather than just min/max
> values. It's just that nobody has put in the work to do the parallel I/O
> for it.
>
> Cheers,
> Ian
>
>
>
> On Thu, Oct 19, 2017 at 9:50 AM, Timo Heister <heister at clemson.edu> wrote:
>
>> > Or are you saying that the topography you output is due to the moving
>> > boundary? In that case, if the boundary would move in perfect response
>> to
>> > the fluid stress underneath, then the "dynamic topography" computed in
>> each
>> > time step would actually be zero, because there are no excess stresses
>> that
>> > aren't already accommodated by the displaced surface!
>>
>> To add to Wolfgang's reply:
>> This is basically how the free surface implementation works, we
>> compute how much fluid wants to move through the surface and move the
>> surface accordingly.
>>
>>
>>
>> --
>> Timo Heister
>> https://urldefense.proofpoint.com/v2/url?u=http-3A__www.math.clemson.edu_-7Eheister_&d=DwIGaQ&c=pZJPUDQ3SB9JplYbifm4nt2lEVG5pWx2KikqINpWlZM&r=Wl19MSBMb4DZXdORUmp5jA&m=LL9fug0ZE7qJZzKQjUMkIsvL0aLvN-x7mpaYSYowf0A&s=8itYzocifGA6w2VjgGfIUF8ggCVaEbTpKqY9aKKwCfc&e=
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>
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>
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>
> --
> Rene Gassmoellerhttp://www.math.colostate.edu/~gassmoel/
>
>
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