very different bedrock velocity using or not the ellipticity peak

[luigiV]

Hi Marc, welcome back to the forum.
I would like to submit this situation where the result of the joint inversion is very different using or not the ellipticity peak. This is evident both in the ellipticity plot and in that of the ground profiles where the bedrock speed ranges from 700m/s to 3000m/s. The ellipticity curve was obtained with HVTFA m = 8 nppm = 5. I tried to use the curve as if it were without singularity or with singularity (right side of the peak), but the result is identical.
The frequency gap between ellipticity and dispersion is approximately equal to 2 and I am aware that it is not optimal.
Can you help me understand why I get these different results?
Thank you
Luigi