A surface evidenee of rupture inside the upper levels of the Aube river alluvial terrace has been detected. The geophysical context is difficult because the accident is of weak amplitude and located just in the subsurface of heterogeneous alluvial materials. Two electromagnetic methods have been implemented and results are presented hereunder. The radio-magnetotelluric method, in which traditionally Ihe only information analysed is the apparent resistivity. is here fully applied wilh a study of the spatial variations of the magnetic field. The GPR method provides a more detailed image of the accident, once detected.