[CIG-SEISMO] SPECFEM3d_Cartesian , using point force with gaussian stf

[Dimitri Komatitsch]

Dear Florian,

Thank you very much for your modification. I have just committed it to 
the official source code on GitHub ("devel" branch).

Thanks!
Best regards,

Dimitri.

On 09/03/2015 12:24 PM, Florian Schumacher wrote:
> Hello!
>
> I came accross the following problem with SPECFEM3d_Cartesian:
>
>
> Looking at the latest code on GitHub, I noticed that the flags
> USE_RICKER_TIME_FUNCTION and USE_FORCE_POINT_SOURCE can now be used
> independently of each other in any combination, which allows for point
> force and moment tensor sources using either, ricker or gaussian source
> time functions (or error function, in case of moment tensor) .
> This is great! (was strongly restricted before).
>
>
> However, there seem to be some remaining old code (in devel branch)
> which prevents this from working properly:
>
> 1) src/specfem3D/setup_sources_receivers.f90 , subroutine setup_sources() :
> t0 is (re)defined as
>    t0 = - 1.2d0 * minval(tshift_src(:) - 1.0d0/hdur(:))
> in case of (USE_FORCE_POINT_SOURCE .or. USE_RICKER_TIME_FUNCTION).
> This (re)definition makes sense if hdur contains dominant frequency, but
> should not happen if you want to use a gaussian for a point source
> (since then the array hdur should actually contain half durations).
>  From what I can conclude at this point, you can fix this simply by
> removing "USE_FORCE_POINT_SOURCE .or." from the if-clause, i.e. execute
> this (re)definition only in case of USE_RICKER_TIME_FUNCTION == .true.
>
> 2) src/specfem3D/compute_add_sources_viscoelastic.f90:
> the function comp_source_time_function_gauss() is always called with a
> fixed half duration value of 5.d0*DT instead of hdur_gaussian(isource).
> Changing this to hdur_gaussian(isource) would give the full
> functionality that I guess is intended here (please do correct me, if
> necessary).
>
>
> Making these two small corrections, the correct source time functions
> are created for all types of sources, having a correct time shift t0.
> I have attached the two relevant files to this email, correcting the
> code (see comments containing "FS FS"). However, in
> compute_add_sources_viscoelastic.f90 I am not entirely sure whether all
> calls to comp_source_time_function_gauss() should be modified as
> described above (though it looks like that to me), because I am not much
> familiar with adjoint or GPU simulations. So please look for all
> comments containing "FS FS". Thanks.
>
>
> There is one little thing though when using a point source and not a
> Ricker wavelet:
> The value of half duration is read from the f0 value in FORCESOLUTION,
> actually meaning a value of half duration and not frequency. In my
> opinion this should not be a problem, since in old SPECFEM3d versions
> this confusion was similar when reading the value of center frequency
> from the hdur line in file CMTSOLUTION.
> Also, when setting f0 = 0.0 in FORCESOLUTION, the variable hdur is set
> to TINYVAL and not to 5*DT which is done in the analogous case of using
> a Moment tensor source with a Heaviside. But the user could simply write
> f0=5*DT to FORCESOLUTION when he needs a steep gaussian.
>
>
> I hope this could help. I am happy about any feedback in case there is a
> better (more suited) solution to this. Thanks!
>
> Florian
>
>
>
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-- 
Dimitri Komatitsch
CNRS Research Director (DR CNRS), Laboratory of Mechanics and Acoustics,
UPR 7051, Marseille, France    http://komatitsch.free.fr