Attenuation in SpecFEM3D and SpecFEM2D

Dear all,

I have a question regarding the differences in attenuation between the algorithms of SpecFEM3D and SpecFEM2D.

If I apply attenuation on my model in SpecFEM2D, it changes wave velocities and time periods heavily.
In SpecFEM3D, only the amplitudes are damped. Why is that?
I have attached an example, in SpecFEM3D I applied Q values of 30 which means a quite strong damping, in SpecFEM2D I applied Q values of 80 for both Q’s which is more moderate. Still, in SpecFEM2D I have a strong difference between both waveforms.

I would be very pleased about an answer,

Thanks in advance,