Home – Home – Jornals – Russian Geology and Geophysics 2022 number 3

Magnetic viscosity is one of the aftereffects inherent in geologic materials. This phenomenon consists in the time lag of changes in the magnetic characteristics of ferromagnetic materials relative to changes in the external magnetic field. Magnetic viscosity in rocks is associated mainly with the magnetization of superparamagnetic particles of ferrimagnetic minerals. In the transient electromagnetic method, magnetic viscosity is manifested as a slowly decreasing voltage induced in a receiving loop or, in some cases, as a nonmonotone transient voltage response. Eddy currents and viscous magnetization arise and decay independently of each other; therefore, the induction transient response measured with a fixed-geometry TEM array gives no way of finding the vertical distribution of magnetic viscosity. To find this distribution requires geometric soundings. At late times, the voltage induced in the receiving loop due to the magnetization decay is vastly larger than that induced by the eddy currents. Therefore, the contribution of magnetic viscosity to the total transient response limits the sounding depth of the transient electromagnetic method.