[CIG-SEISMO] simulation of seismic wave propagation excited by a force

[Yang Luo]

I think Daniel (or someone else) has already copied necessary lines from old package.

There is an option "USE_FORCE_POINT_SOURCE" in constant.h, which allows one to use a point force
(which Yingzi already figured out, or maybe it's already in the manual)
  logical, parameter :: USE_FORCE_POINT_SOURCE = .false.
  double precision, parameter :: FACTOR_FORCE_SOURCE = 1.d15
  integer, parameter :: COMPONENT_FORCE_SOURCE = 3  ! takes direction in comp E/N/Z = 1/2/3

Interpretation is included, if the point force is not located exactly on a GLL point.






________________________________________
From: Dimitri Komatitsch [komatitsch at lma.cnrs-mrs.fr]
Sent: Tuesday, September 11, 2012 12:01 PM
To: Yingzi Ying
Cc: cig-seismo at geodynamics.org; Joseph Charles; Paul Cristini; 谢志南; Yang Luo; Christina Morency
Subject: Re: [CIG-SEISMO] simulation of seismic wave propagation excited by a   force

Dear Yingzi,

You are right, in the current code there is no option in the Par_file to
use a point source, but we added this to the todo list right before the
summer and thus we should/will definitely do it. It is easy to do: just
add the Ricker wavelet to the accel() vector (which is in fact a force
vector before we divide it by the mass matrix), to the component you
want (vertical or horizontal) and you are all set.

Joseph, could you maybe do it? below are a few lines from one of my test
codes, in which I do just that; let us cut and paste these lines in
SPECFEM3D (it is just a matter of selecting the right grid point; which
we already do for a CMT source, thus we could add a force instead of a
CMT at that location; the only difference being that the CMT source is
added to all the points of a given spectral element, while a force
vector should be added to a single point).

Let me talk to Joseph tomorrow to see if we can release a patch of the
source code soon.

I also cc Yang to see if he has already done that in a local version at
Princeton maybe (for instance to model a force for some of his oil
industry simulations in foothill regions?).

Another difficulty is if the location of the force does not correspond
to a grid point; then there are two options:

- select the closest grid point; i.e. slightly change the location of
the source (can be done automatically by the code)

- use Christina Morency's way of adding a force source between grid
points; I think I remember she did that in the 2D code, but I am not
sure how; thus I cc her.

(that second option would be better, if Christina can confirm that it
works fine)

Best wishes,
Dimitri.

==================================================================

! ipoinsource is the global grid point at which we add the source
! "3" means a vertical force (i.e. we add the force to the vertical
! component of the force vector, which is later divided by the mass
! matrix to get the acceleration vector)
! factor_force is the norm of the force vector to add
! ricker(t) is the Ricker wavelet at time t = (it-1)*deltat

   accel(3,ipoinsource) = accel(3,ipoinsource) - factor_force * ricker(t)

==================================================================

On 09/11/2012 12:59 PM, Yingzi Ying wrote:
> Hi all,
>
> I am trying to use specfem3d to simulate waves excited by a vertical
> force with user-defined source forms such as ricker wavelet.
>
> I tried to do it through adjoint simulation by setting 'SIMULATION_TYPE
> = 2' and put source position at STATIONS_ADJOINT and receivers at
> CMTSOLUTION. But I failed.
>
> Does anyone have an idea or suggestion how to do active simulations with
> specfem3d?
>
> Thanks in advance.
>
> Best regards,
> Yingzi
>
>
> _______________________________________________
> CIG-SEISMO mailing list
> CIG-SEISMO at geodynamics.org
> http://geodynamics.org/cgi-bin/mailman/listinfo/cig-seismo

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