ИСТИНА

Much emphasis has been put in the past into studies of the ultra low frequency (ULF) electromagnetic (EM) effects possibly related to the impending earthquakes. Knowledge of the source mechanisms of ULF EM field is of paramount importance when discussing possible candidate of earthquake precursors. This report focuses on the overview of modern models and underlying physical mechanisms explaining generation of the ULF EM fields in the Earth’s crust. These models can be split into two general classes, depending on whether they deal with electric- or magnetic-type dipole as an underground sources of the ULF fields. The first class of the models includes electrokinetic effect arising from underground fluid migration under the influence of tectonic stress, and stress-produced electric current caused by variations of the rock conductivity due to changes in mobility of point and linear defects of atomic lattice. Energization of crack formation in the vicinity of fault zone brings the electric charges accumulate at the crack surface thereby exciting random electric fields and currents in the rock. The second class of theoretical models based on perturbations of the Earth’s magnetic field is considered. This kind of perturbations can be associated with the acoustic emission of the cracks, which results in excitation of electric current due to motion of the conductive ground in the Earth’s magnetic field. In the case of tensile cracks the effective magnetic moments of the crack-produced currents are co-directed since all the moments are pointed oppositely to the vector of Earth magnetic field. Rough estimates of these effects are derived in this report to compare the amplitudes produced by the underground EN sources in the atmosphere. It follows from these estimates that further experiments are necessary to sort out this interesting problem in ULF fields and to distinguish between the various competing theories.