The TEM Method in Studies of Near-surface Magnetically Viscous Rocks

The paper discusses the effect of magnetically viscous near-surface rocks on the TEM response. In geological materials magnetic viscosity is caused predominantly by relaxation of magnetization of superparamagnetic mineral grains. Magnetic viscosity is shown to have a pronounced effect on the TEM data. More often than not it is regarded as a noise hampering the interpretation of TEM data in terms of conductivity. By contrast, we show, through forward calculation of TEM responses and inversion of the field TEM data in terms of time-dependant magnetic susceptibility, how magnetic viscosity effects can be used as a source of important information on the near-surface geology.