[1] We present experimental results of a study of electromagnetic field generation during underground detonation of high explosive charges in holes bored in sandy loam and granite. Three components of electric field (vertical component in air and two horizontal components in the soil) and three components of the magnetic induction were recorded during the field experiments. Test conditions and physicomechanical properties of the soil exert significant influence on the parameters of electromagnetic signals generated by underground explosions with masses of 2-200 kg. The electric and magnetic field experimental data are satisfactorily described by an electric dipole model with the source embedded in layered media. We used the solution for a field produced by stationary vertical and horizontal electric dipoles placed near the interface between two layers with different conductivity. The magnitude of the field source was estimated on the basis of the records of electromagnetic signals obtained at different distances from the borehole. For an underground explosion of a TNT charge with a mass of 2 kg carried out in granite the maximum estimated value of the electric dipole component is about 10 À7 C m. This estimate is more than an order of magnitude greater than that obtained for an explosion of the same mass carried out in sandy loam.

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[1] Experimental results of a study of electromagnetic fields due to detonation of high explosive charges with mass of a few kilograms are presented in this paper. Data show that in the initial stage of explosion the fields decrease as the fourth power of distance. Such a quadrupolar type of field contradicts the concept that an explosion is characterized by an effective electric dipole. A theoretical analysis is given based on expansion of an electromagnetic field in multipole moments. The theory is used to make estimates of the quadrupolar and dipole moments of the electric charge system resulting from an explosion occurring at the Earth's surface; calculations of electric fields thus produced are similar to those observed.

A low‐frequency electric field is observed during crater formation by detonation of high explosive charges. The disturbance of the atmosphere's electric potential gradient at ground level was measured in the range of frequencies between 0 and 200 Hz. Our results indicate that explosions are capable of creating large electrical charge separations in the atmosphere. A simple model of field generation is proposed. Furthermore, a correlation between the magnitude of the explosion and the electric charge of the dust cloud is established. Using these results, estimates of the intensity of the electric field generated during meteorite impact crater formation is proposed.

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