[CIG-SEISMO] [SPAM: 7.000] Re: get_attenuation_scale_factor error

[Robin Lee]

Hi Dimitri,

Thank you very much for your answer, and apologies for the (very) late reply, I have been busy with a few other things but am back to addressing this issue with attenuation now.

I'm afraid I'm a bit unsure about what this Q value specfem refers to represents. For our velocity model, the lowest Vs is 0.5km/s and we are using the correlations from Graves (2010), Qs = 50Vs and Qp = 2Qs, which for this case is Qs = 25 and Qp = 50. Is this attenuation too high for specfem3D? Or am I misinterpreting something?

Regards
Robin

________________________________________
From: Dimitri Komatitsch [komatitsch at lma.cnrs-mrs.fr]
Sent: Friday, July 29, 2016 7:48 PM
To: cig-seismo at geodynamics.org; Robin Lee
Subject: [SPAM: 7.000] Re: [CIG-SEISMO] get_attenuation_scale_factor error

Hi Robin,

Q = 4 means attenuation is extremely large. You maybe then need to
switch to the "SolvOpt()" routine that we put in the 2D code. See
http://komatitsch.free.fr/preprints/GJI_Lombard_2016.pdf and
https://github.com/geodynamics/specfem3d/issues/742

You should also check your reference frequency
(ATTENUATION_f0_REFERENCE) because the correction factor you get (0.37)
is extremely big (the reference value being 1.).

Are you sure the viscoelastic wave equation remains a valid model for
such a medium?

Best regards,
Dimitri.

On 29/07/2016 06:31, Robin Lee wrote:
> Hi all,
>
> I've been attempting to implement attenuation in a tomography model
> which I have been running. It seems to run fine without attenuation, but
> once I add in Qp and Qs, and set the attenuation to .true. in the
> Par_file, I get an error in the gen_databases step which states the
> following:
>
> error : in get_attenuation_scale_factor()
>    scale factor:   0.37110551337678144       should be between 0.7 and 1.3
>    Q value =    4.3168292045593262       central frequency =
> 5.3879655900887585E-002
>    please check your reference frequency ATTENUATION_f0_REFERENCE in
> constants.h
>  unreliable correction factor in attenuation model
>  Error detected, aborting MPI... proc            0
> --------------------------------------------------------------------------
> MPI_ABORT was invoked on rank 0 in communicator MPI_COMM_WORLD
> with errorcode 30.
>
> NOTE: invoking MPI_ABORT causes Open MPI to kill all MPI processes.
> You may or may not see output from other processes, depending on
> exactly when Open MPI kills them.
> --------------------------------------------------------------------------
>
> I am currently using a simple correlation of Qs=50Vs and Qp=2Qs where Vs
> is in km/s. I have looked in the constants.h file but cannot actually
> find the ATTENUATION_f0_REFERENCE parameter. Has anyone experienced this
> error before, know what is going wrong or know how to fix it?
>
> Regards
> Robin
>
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--
Dimitri Komatitsch
CNRS Research Director (DR CNRS), Laboratory of Mechanics and Acoustics,
UPR 7051, Marseille, France    http://komatitsch.free.fr

This email may be confidential and subject to legal privilege, it may
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please notify the sender immediately and erase all copies of the message
and any attachments.

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