[CIG-SEISMO] SPECFEM2D absorbing condition with internal mesher

[giuseppe.digiulio at ingv.it]

Dear specfem developers

I am an Italian researcher and I am using the specfem2D code aimed to  
simulate vey simple 2D topographic irregularities.

My doubt now is on how to select the absorbing boundaries layers when  
the internal meshing of the code is used.

In my simple 2D P-SV model based on two layers I have three  
interfaces: i) the superficial topography, ii) the interface  
separating between first and second layer, iii) and the bottom  
interface.
Note that the first and second layer in my example have exactly the  
same properties (Vs, Vp, Q etc) and therefore the internal interface  
is ficticious (and should be in my will transparent).

My source was placed in the second layer.

I want that the uppermost topographic interface and the internal  
interface (the one separating layer #1 and #2) are not absorbing, on  
the contrary I want that the bottom, the left/right interfaces are  
absorbing.

But my 2D simulations seem to show that also the internal interface  
(the one separating layer #1 and #2) is perfectly absorbing too. This  
of course produces nearly null X and Z output at the receivers  
situated just along the surface topography.


Is it correct? or I wrong in some other point? How can I have the  
internal interface not absorbing at all?
Suggestions are of course very welcome.

Follow details on the parameters used in my 2D model:

In Par file my selection concerning absorbing conditions was

# external mesh or not
read_external_mesh              = .false.

# absorbing boundary active or not
absorbing_conditions            = .true.
# absorbing boundary active or not
PML_BOUNDARY_CONDITIONS         = .true.
NELEM_PML_THICKNESS             = 4
STACEY_ABSORBING_CONDITIONS     = .true.
ADD_SPRING_TO_STACEY            = .false.


   # PARAMETERS FOR INTERNAL MESHING

# absorbing boundaries parameters
absorbbottom                    = .true.
absorbright                     = .true.
absorbtop                       = .false.
absorbleft                      = .true.



For clarity I provide in the attachment the Par_file, interface,  
SOURCE and  a logmessage file following my 2D test. I am using the  
7.0.0 release.

Thanks in advance
Giuseppe Di Giulio

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