[CIG-SEISMO] Issue with material properties in SW4 (Shahar Shani-Kadmiel)

[Petersson, Anders]

Dear Shahar,
SW4 currently outputs the zero frequency limit of (Cp, Cs) and that is
what you see in your image files. When the material model is
visco-elastic, the material is dispersive and the phase velocities depend
on frequency. Unless the attenuation parameters (Qp, Qs) are very small,
the values of (Cp, Cs) you see in the image file will be close to the
specified values. In your model, you use Qp=3 and Qs=2 at the surface.
Such low values lead to a significant frequency dependency of (Cp, Cs).
Note that Cp(f) and Cs(f) also depends on the phasefreq and maxfreq
parameters as well as the number of mechanism in the attenuation command.
See the SW4 user's guide for further details.
/Anders

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>   1. Issue with material properties in SW4 (Shahar Shani-Kadmiel)
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>----------------------------------------------------------------------
>
>Message: 1
>Date: Tue, 22 Mar 2016 15:50:07 +0200
>From: Shahar Shani-Kadmiel <kadmiel at post.bgu.ac.il>
>To: cig-seismo at geodynamics.org
>Subject: [CIG-SEISMO] Issue with material properties in SW4
>Message-ID: <2836CC82-5ED7-494D-98C1-0A68A0C4C56D at post.bgu.ac.il>
>Content-Type: text/plain; charset="utf-8"
>
>I am trying to prescribe a custom gradient to material properties as the
>builtin gradient option in SW4 does not apply to Qp and Qs and also
>because I am interested in a slightly more complex gradient than a simple
>linear one. When checking the material properties stored in the images
>written by SW4 I noticed that the values are off by quite a bit.
>
>I have created a sample input file which produces the issue that can be
>downloaded here 
><https://www.dropbox.com/s/eoao8l6wdxtmfyg/material_test.sw4?dl=1>.
>
>I don't really understand where the issue originates. It might be just
>wrong data in the SW4 image file(I hope that is the case) because SW4
>reports the correct values in stdout (full stdout here
><https://www.dropbox.com/s/0mycmrfi66tr2p4/stdout.txt?dl=1>):
>
>       ----------- Material properties ranges ---------------
>       1.61000000e+03 kg/m^3 <=  Density <= 1.99000000e+03 kg/m^3
>       6.50000000e+02 m/s    <=  Vp      <= 9.64000000e+02 m/s
>       3.50000000e+02 m/s    <=  Vs      <= 6.66000000e+02 m/s
>       1.44736842e+00        <=  Vp/Vs   <= 1.85714286e+00
>       1.97225000e+08 Pa     <=  mu      <= 8.82676440e+08 Pa
>       5.95263090e+07 Pa     <=  lambda  <= 2.85775000e+08 Pa
>       Using attenuation
>       2.00000000e+00        <=  Qs      <= 5.20000000e+01
>       3.00000000e+00        <=  Qp      <= 1.03000000e+02
>       ------------------------------------------------------
>Below is a workflow to demonstrate the issue: (viewable as a static
>notebook here 
><http://nbviewer.jupyter.org/urls/dl.dropbox.com/s/gakmdsneom6kesu/SW4_Mat
>erialModel_Issue.ipynb>)
>
>First I parse the input file
><https://www.dropbox.com/s/eoao8l6wdxtmfyg/material_test.sw4?dl=1> and
>plot the desired material properties as they are specified in the block
>commands.
>I then read the Vp, Vs, and rho, cross section images created by SW4 and
>plot the images
>I then plot a sample column from the center of each image array to
>present the resulting material properties.
>Finally I compare the desired and resulting properties side by side and
>report the min, max, values.
>I guess I would like to know if this issue is reproducible on other
>machines and if so if it is a real issue? That is: Does the SW4
>computation actually runs with wrong material properties or does it
>simply report the wrong values in the image files.
>
>Thanks for your help,
>
>Shahar
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