After a few tests to check the likelihood of our measurements on the length and distribution of the reflections, we can show that the study of the reflectors in the layered lower crust recorded on SWAT seismic sections, may help to understand the Permian crumbling of the variscan orogen. The creeping of the variscan root towards the Hercynian front was responsible for the extension of the mafic reflectors during Permian time. This regional extension was contemporaneous with a more local stretching recorded beneath the variscan thrusts.