[CIG-SEISMO] get_attenuation_scale_factor error

Mon Sep 5 02:55:30 PDT 2016

Hi Robin,

Thanks!
The routine is in src/specfem2D/attenuation_model.f90 .

Best regards,
Dimitri.

On 05/09/2016 01:31, Robin Lee wrote:
> Hi Dmitri,
>
> Thank you, I have read the paper and this may very well be the issue I am facing. I have looked through specfem2D a bit but can't seem to find where the SolverOpt() is implemented. Would you be able to point me to where it is?
>
> Regards
> Robin
> ________________________________________
> From: Dimitri Komatitsch [komatitsch at lma.cnrs-mrs.fr]
> Sent: Sunday, August 28, 2016 9:01 AM
> To: Robin Lee; cig-seismo at geodynamics.org
> Subject: Re: [SPAM: 7.000] Re: [CIG-SEISMO] get_attenuation_scale_factor error
>
> Hi Robin,
>
> Q = 25 or above is classical and works fine, no problem.
> However there is likely an error in the routine you use to build your
> velocity model, since it gives you mesh points at which Q = 4, and in
> that case yes SPECFEM3D can become unstable (easy to fix, see
> http://komatitsch.free.fr/preprints/GJI_Lombard_2016.pdf , and already
> fixed in the 2D code; we never took the time to fix the 3D code as well
> because such very low Q values never occur in practice).
>
> It is likely your velocity model routine that gives fictitious very low
> Vs or Vp values at at least one location.
>
> Best regards,
> Dimitri.
>
> On 27/08/2016 18:10, Robin Lee wrote:
>> 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
>> not reflect the views of the University of Canterbury, and it is not
>> guaranteed to be virus free. If you are not an intended recipient,
>> please notify the sender immediately and erase all copies of the message
>> and any attachments.
>>
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>> information.
>>
>
> --
> 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
> not reflect the views of the University of Canterbury, and it is not
> guaranteed to be virus free. If you are not an intended recipient,
> please notify the sender immediately and erase all copies of the message
> and any attachments.
>
> Please refer to http://www.canterbury.ac.nz/emaildisclaimer for more
> information.
>

-- 
Dimitri Komatitsch
CNRS Research Director (DR CNRS), Laboratory of Mechanics and Acoustics,
UPR 7051, Marseille, France    http://komatitsch.free.fr