[CIG-SEISMO] get_attenuation_scale_factor error / PS

Mon Oct 17 09:00:35 PDT 2016

Hi Robin,

Thanks! Very strange though, I am pretty sure their analysis is wrong 
because calling SolvOpt() is used to compute the relaxation times 
tau_sigma and tau_epsilon and nothing else, and that does not depend on 
the spatial dimension of the problem.
As you can see in 
http://komatitsch.free.fr/preprints/GJI_Lombard_2016.pdf we developed it 
in the 1D case and it then took 10 minutes to plug it into the 2D code.

Best wishes,
Dimitri.

On 17/10/2016 00:47, Robin Lee wrote:
> Hi Dimitri,
>
> I've attempted to implement the SolvOpt() routine in the specfem3d code but unfortunately was not successful. I followed up on this by talking with some programmers in our research group but they said that it looked quite difficult and seemed like it would require a lot of work to change from 2D to 3D. At the end of the day it seems I am unable to help out with this, my sincerest apologies.
>
> Regards
> Robin
> ________________________________________
> From: Dimitri Komatitsch [komatitsch at lma.cnrs-mrs.fr]
> Sent: Wednesday, September 07, 2016 9:08 AM
> To: cig-seismo at geodynamics.org; Robin Lee
> Subject: Re: [CIG-SEISMO] get_attenuation_scale_factor error / PS
>
> Hi again Robin,
>
> PS: if you implement it please let us know and email us the modified
> version and we will make it the official version on our Git server (see
> https://github.com/geodynamics/specfem3d/issues/742 ).
>
> Thanks,
> Best regards,
> Dimitri.
>
> On 05/09/2016 11:55, Dimitri Komatitsch wrote:
>>
>> 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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>>>>>
>>>>> _______________________________________________
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>>>>> CIG-SEISMO at geodynamics.org
>>>>> http://lists.geodynamics.org/cgi-bin/mailman/listinfo/cig-seismo
>>>>>
>>>>
>>>> --
>>>> 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
>>>
>>> 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
>
> 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