[CIG-SEISMO] get_attenuation_scale_factor error / PS

Tue Sep 6 14:08:17 PDT 2016

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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>>>>
>>>> _______________________________________________
>>>> CIG-SEISMO mailing list
>>>> 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