A method for mapping geological structures of a formation on a side of a surface, includes: generating a magnetic moment using at least one magnetic moment generator to build up a magnetic field in the formation in an on-period, wherein the magnetic moment has a moment strength, and wherein the magnetic moment is positioned on another side of the surface; changing the magnetic moment to change the magnetic field; and making at least one record in a recording device at a recording time trecord in an off-period, wherein the record includes at least a representation of the change in the magnetic field and/or a representation of the magnetic field obtained by a B/E-measuring unit; wherein the on-period is separated from the off-period by the act of changing the magnetic moment.