[CIG-SHORT] RELAX Question

[Austin Madson]

Prof. Barbot,

Thanks again for the response - you've been  very helpful thusfar.

Just to confirm:
Trying to get at displacement units (let's call them km). If my inputs are
the following, and I divide out the 1e3 from the displacement field - the
units are just that, km. Is that correct? Or, if I keep the Lamé parameters
(along with t3)  in GPa instead of kPa - does the Gamma value then = 8.33e2
[gamma=8.33e2 = (1-0.25)*3400*9.8/30 or gamma=8.33e4 =
(1-0.25)*3400*9.8/30000000 ],  and we still divide out the 1e3 from the
displacement to get the units in "km"?



Cheers and thanks!

Austin M




# grid dimension (sx1,sx2,sx3)
512 512 512
# sampling (dx1,dx2,dx3), smoothing (beta, nyquist)
0.9765625 0.9765625 0.9765625 0.2 0
# origin position (x0,y0) and rotation
0 0 0
# observation depth (displacement and stress)
0 0
# output directory
$WDIR
# lambda, mu, gamma (gamma = (1 - nu) rho g / mu)
30 30 8.33e-4
# time interval, (positive time step) or (negative skip, scaling)
1 1 1
# number of observation planes
0
# number of observation points
0
# number of stress observation segments
0
# number of prestress interfaces
0
# number of linear viscous interfaces
0
# number of nonlinear viscous interfaces
0
# number of fault creep interfaces
0
# number of inter-seismic strike-slip segments
0
# number of inter-seismic tensile segments
0
# number of events
1
# number of coseismic strike-slip segments
0
# number of coseismic tensile segments
0
# number of coseismic dilatation point sources
0
# number of surface loads
1
# nb x1 x2 length width t3 T phi
1 0 0 3.937 3.937 20 0 0
EOF


On Tue, Jan 19, 2016 at 11:20 PM, Sylvain Barbot <sylbar.vainbot at gmail.com>
wrote:

> Hi Austin,
>
> I often get questions about units. There are no formal choice of units
> in Relax, except that S.I. units, or more precisely, their
> inter-relationships, is assumed. The expected input of the current
> version of Relax is
>
> n x1 x2 length width t3 T phi
>
> where n is the index, x1 and x2 and north and east, length and width
> are the dimension of the source patch, t3 is the traction (force per
> unit area), and T and phi is the period and phase assuming the
> following model
>
> p(t)=t3*sin(2*pi*t/period+phi)
>
> t3 is the load in units of stress. If you prescribed your Lamé
> parameters in units of MPa, you need to describe the load in MPa.
>
> I apologise that the examples I sent you correspond to an old version
> of Relax. The current version assumes stress units. (The previous
> version expected t3/G.) The factor of 1,000 comes in depending on your
> choice of length units. If you use km, it introduces a factor of 1,000
> in the displacement field. You can compensate this effect by dividing
> the rigidity by the same factor.
>
> Cheers,
> Sylvain
>
>
> On Wed, Jan 20, 2016 at 2:03 PM, Austin Madson <amadson at ucla.edu> wrote:
> > Prof. Barbot,
> >
> > Thanks for the response and the example data. I am working out my
> parameters
> > (and units now). I think I have a lock on the elastic and viscoelastic
> > params. However, I am having trouble with the load parameters.
> >
> > I see that on some of your input files the surface load/traction
> parameters
> > are;
> > nb x1 x2 length width t3 T phi
> >
> > and another has;
> > nb x1 x2 t3 length width T phi
> >
> > I assume the former is correct, yes?
> >
> > Also, I'm trying to wrap my head around the units for force(t3). In the
> > GRACE example (the _km.xyz file), the z is used in the following
> calculation
> > ($3*9.8/3e10) in order to get force(t3). What are the initial units in
> the
> > _km.xyz file for the third column, z? And what are the units after the
> > calculation ($3*9.8/3e10) in order to derive force(t3)?
> >
> > Also, it appears that the output vertical (z) displacement units are in
> mm,
> > may I assume that is correct?
> >
> > Cheers and thanks A LOT for your responses!
> > Austin M
> >
> > On Tue, Jan 19, 2016 at 9:29 AM, Sylvain Barbot <
> sylbar.vainbot at gmail.com>
> > wrote:
> >>
> >> Hi Austin,
> >>
> >> The Tibet lakes have a great loading signal. You can use Relax to
> >> simulate the deformation, but you need to be careful about how
> >> important the elastic stratification is. If your data are close to the
> >> source, you're fine. I presume you are using paleo-shoreline data. If
> >> so, use the shallow rigidity for the entire domain. If you are
> >> modeling far-field data, you should use a code that have a layered
> >> elastic structure, i.e., (Farrell, 1972).
> >>
> >> The example attached models the deformation from the Indian monsoon
> >> using Grace data. The example cycleload.sh creates a periodic surface
> >> load.
> >>
> >> Best wishes,
> >> Sylvain
> >>
> >>
> >>
> >> On Tue, Jan 19, 2016 at 10:51 AM, Austin Madson <amadson at ucla.edu>
> wrote:
> >> > Professor Barbot,
> >> >
> >> > Thanks for the prompt response. I looked at the documentation and the
> >> > man
> >> > page (as well as the examples on the PDF on the geodynamics website)
> and
> >> > have made progress.
> >> >
> >> > As an fyi, we plan on modeling several hundred years of surface
> loading
> >> > from
> >> > very large lakes (i.e. time dependent loads). Are there any RELAX
> >> > surface
> >> > load examples laying around (they can just be single/multiple point
> and
> >> > even
> >> > instantaneous (no time function)? The GRACE example on the example pdf
> >> > "hides" the data in various dat files (which makes sense if you're
> using
> >> > a
> >> > lot of data, but it's hard to see their example inputs).
> >> >
> >> > I expect to see only millimeters of deformation throughout the run -
> >> > will
> >> > the outputs be precise enough if I use the correct SI units
> throughout?
> >> >
> >> > Cheers,
> >> > Austin Madson
> >> >
> >> > On Sun, Jan 17, 2016 at 4:06 PM, Sylvain Barbot
> >> > <sylbar.vainbot at gmail.com>
> >> > wrote:
> >> >>
> >> >> Hi Austin,
> >> >>
> >> >> The details of the input file for surface loads are in the
> >> >> documentation
> >> >> and in the man page. There are some pdf files on the geodynamics
> >> >> website
> >> >> that show examples of surface loads for the Himalayan region if I
> >> >> recall
> >> >> well.
> >> >>
> >> >> But the input file simply expects a list of squares with their
> >> >> associated
> >> >> traction. So depending on your project, this can be a single point,
> say
> >> >> to
> >> >> represent the loading of a dam, or a complicated function of space
> and
> >> >> time.
> >> >> If your change of load is instantaneous, you need only one event. Of
> >> >> your
> >> >> load is time dependent, you need as many events as you have time
> steps.
> >> >> I
> >> >> can be more specific, but I need more information about your
> practical
> >> >> goals.
> >> >>
> >> >> Cheers,
> >> >> Sylvain
> >> >>
> >> >>
> >> >> On Monday, January 18, 2016, Austin Madson <amadson at ucla.edu> wrote:
> >> >>>
> >> >>> Professor Barbot,
> >> >>>
> >> >>> I have a quick question re: RELAX - Is there any more information
> out
> >> >>> there with respect to utilizing RELAX for deformation responses to
> >> >>> surface
> >> >>> loading? I have looked through all of the examples as well as the
> >> >>> slides/tutorials on the geodynamics.org website.
> >> >>>
> >> >>> Can you provide any further information? Or can you point me in a
> >> >>> better
> >> >>> direction?
> >> >>>
> >> >>> Cheers,
> >> >>> Austin Madson
> >> >
> >> >
> >
> >
>
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