Modeling of non-stationary electrokinetic effect in a conductive crust

The magnetic field, generated by the electrokinetic effect is calculated for a spherical, time-varying pressure source in a layered half-space chosen due to its exact solvability. In addition to a widely discussed steady-state phase, electromagnetic signals of electrokinetic origin have a transient phase which corresponds to their propagation through a conductive crust. The duration of the transient phase depends on a distance from there pressure gradient source and on the crustal conductivity. For characteristic conductivities of 0.1-10-3 S/m and distances of several kilometers the transient phase lasts for 10-100 sec. Although in the layered model both transient and steady state external magnetic fields are zero, this is not so in the general case. Therefore, if the electrokinetic effect occurs in a water filled fault, the transient magnetic field can appear at the surface as an ULF pulse.