Fundamental 2 layer analysis [SPECFEM2D]

Hi all,

I am running a forward simulation with SPECFEM2D on a very simple case: 2 horizontal layer model. The aim is to see the wiggle of the seismic trace itself and compare it with that one of a convolutional model. Both materials are acoustic with velocities 1000 m/s (top layer) and 2000 m/s (bottom layer). The interface is 1500 meters from the bottom and the Ricker wavelet is used (figure attached).

However, as exposed in the second figure, the SPECFEM seismic trace (in red) shows a bumpy area at the beginning whose origin I don’t get to see. It’s fair that the energy in the seismic trace seems to be conserved, but could someone shed some light on the initial bump?


PS: I am not able to upload, so the figures can be found in this link: zz_sharepost - Google Drive