HIGH ELECTRIC FIELDS IN THE EARTH’S INTERIOR AND THEIR POSSIBLE ROLE IN GEOLOGICAL AND GEOCHEMICAL PROCESSES AND IN MINING

A. A. VOROB’EV

Many physical processes in the Earth’s geospheres, in the atmosphere, and in near-Earth space are considered in their mutual interrelation [1].

In the known theoretical schemes, the case of a lightning strike into the ground or into a grounded object is considered, as well as the spreading of the direct-strike current, the occurrence of step voltages in the ground, etc. The formation of high electric fields at the ends of grounded objects and cases of discharge propagation from grounded objects into the atmosphere are considered. Until now, the occurrence of high electric fields in the lithosphere and the possibility of various processes in the Earth’s interior under the action of high electric fields have not yet been considered. The Earth’s surface has usually been regarded as the boundary of the region in which high electric fields exist in the atmosphere. In dielectric rocks, both those exposed at the surface and those located in the interior, high electric fields and discharges in them may arise. The causes of the occurrence of high fields in dielectric rocks under conditions of occurrence may be a direct lightning strike into the ground, the phenomenon of electric induction during the passage of a charged cloud, electromagnetic induction caused by large currents in the ionosphere, frictional phenomena, rock destruction, irradiation, and other physical processes occurring outside the Earth’s interior. Some of the processes named are a means of transferring energy from near-Earth space into the Earth’s interior and of replenishing the planet’s energy reserves. The formation of a crack in a dielectric mineral or rock is accompanied by electrification of its sides and by the formation of a high-intensity field in the crack. Thus, crack formation appears as a means of converting mechanical energy into the energy of an electric field, and the crack is an electrostatic generator.

We have advanced a hypothesis concerning the possibility of electrical discharges in the Earth’s crust, which has been substantiated experimentally and theoretically [2, 3]. Under terrestrial conditions, various physical transformations of certain kinds of energy into the energy of an electrostatic field are possible, accumulating charges up to a value at which the field strength reaches the magnitude of the electric strength of rocks, and electrical discharges occur in the medium [4]. High electric fields in the Earth’s interior and their manifestation above the surface—the high atmospheric electric field—may be formed at a high density

electric charges in dielectric rocks of high resistance. A state of high concentration of charges is not characteristic of a system in stable equilibrium. It is characteristic of a system in a state with a large excess of free energy. For example, when rock masses are close to failure, and an area is close to an earthquake.

High electric fields should be sought in areas of deep faults, in rock masses in which large reserves of elastic energy have accumulated.

It has been noted many times that in the area of the future epicenter of an earthquake there have been observed luminescence of the atmosphere, electrical storm discharges, glowing of luminescent lamps and screens, anomalies of the atmospheric electric field, breakdown of insulation in cables lowered into boreholes, anomalies of the magnetic field and the presence of a large vertical component of the field, and many other phenomena whose cause can only be a high electric field in the region of the focus of the future earthquake. All the listed phenomena disappeared after the first underground shock.

The consequence of powerful electrical discharges in the Earth’s crust may be seismic and various other geoelectric phenomena associated with changes in the characteristics of the electromagnetic field in the interior and above the Earth’s surface, which are observed before an earthquake. A change in the electric field in the atmosphere owing to the accumulation of a local charge in the interior may influence electrical processes in the atmosphere and the course of pre-thunderstorm phenomena, as well as currents in the Earth.

In the plasma of electrical discharges in the Earth’s interior, just as in discharges in the atmosphere, plasmochemical reactions of combination and decomposition may occur, as a result of which chemical compounds and elements are formed: hydrogen, oxygen, carbon, metals that are constituents of rocks, including oil and natural combustible gases. Compounds could have formed in plasmochemical reactions in cavities that had previously existed in rocks and could have filled them. For example, in limestones containing water, decomposition reactions could have proceeded in the discharge plasma, accompanied by the production of hydrogen and carbon. In subsequent discharges, methane was formed from carbon and hydrogen, and later still heavier hydrocarbons, which are constituents of oil and natural combustible gas.

The examples given show that processes of formation of chemical compounds or production of chemical elements, their migration and redistribution in the Earth’s crust may occur at the expense of the energy of the electric field.

With a large value of the energy released in a discharge in the Earth’s crust, and with small losses, the plasma can be heated to a temperature at which nuclear processes may be possible, the formation of radioactive atomic nuclei, and replenishment of the stock of radioactive materials in the Earth’s crust. In addition to processes of transformation of forms of energy into the energy of an electrostatic field, known from laboratory and industrial practice, as well as from observations of natural phenomena in the Earth’s interior, other specific transformation processes are also possible, determined by metamorphism, tectonic and other geophysical phenomena specifically inherent only to the Earth’s interior. The consequences of the occurrence and propagation of electrical discharges in the Earth’s crust are observed when lightning discharges onto the Earth’s surface. Fused materials in the discharge channel in sandy-clayey rocks, called fulgurites, are often found in the surface layers of soil. In some cases fulgurites up to 10 meters long have been observed. If for porous rocks the discharge volta—

if the field strength is taken to be equal to \(10^3\) V/cm, then a discharge over the length of such a fulgurite occurs at a voltage of \(10^6\) V. Electric voltages of such magnitude and higher during lightning discharges have been recorded. Under laboratory conditions, the accumulation of electric charges in minerals, glasses, and polymers, and the formation of discharges in charged dielectrics, have been observed. Pieces of various sizes were taken for the experiments [4]. A mathematical and physical theory has been developed for dielectrics charged by streams of charged particles—electrons, protons, or high-energy photons [1]. On the basis of the phenomena of charging of dielectrics with a volume of several tens of cubic centimeters and of discharges in them observed in laboratories, the phenomena of charging of minerals and rocks in the Earth’s interior and of discharges in them, likewise in small volumes, are described. In our hypothesis, the regularities obtained are extended to the phenomena of charging and discharges in rocks with volumes of several tens of cubic kilometers. Accumulation of charges is also possible in rock voids filled with liquid and gas. In the latter case, electrification may occur as a result of the same processes that cause electrification in the atmosphere. Using detailed data characterizing the Tashkent earthquake of magnitude eight on April 26, 1966, we calculated the electrical parameters of the earthquake focus. It turned out that the seismic, electrical, and light phenomena observed before the Tashkent earthquake can be explained by assuming that an electric charge of \(10^4\) C was concentrated in the earthquake focus with a volume of \(68\ \text{km}^3\).

The electrical calculation of the earthquake-focus parameters on the basis of the initial instrumental data was carried out in three variants. Values were obtained for the charge, field strength, charge density, and other quantities, all of a reasonable order of magnitude.

In an electric field directed along the radius of the Earth, in the presence of gradients of temperature, pressure, and density of materials, slow growth of an initiated discharge, melting of rocks, and the formation of a through channel connecting the surface of the Earth’s crust with its base are possible. Under such conditions, melting of mantle material will occur at the mouth of the channel under consideration, and a volcanic or mud eruption will take place.

The time until breakdown of rocks in the Earth’s interior decreases as the value of the field strength increases. At a certain depth, under the simultaneous action of petrostatic pressure and the geothermal gradient, the time until breakdown reaches a minimum value. As the field strength increases, the depth of occurrence of rocks for which the time until breakdown will be minimal shifts toward the center of the Earth. Under these conditions, breakdown of rocks will begin in the region where the time until breakdown is maximal and will propagate radially both into the depths and toward the Earth’s surface. As the discharge grows in the dielectric toward the surface, the field strength at its head will increase and the rate of its advance will grow. Propagation of the discharge toward the center of the Earth will be hindered by the increase in conductivity and the decrease in the value of the field strength at the head of the discharge channel. The course of these phenomena explains the growth of a discharge channel toward the daytime surface and the phenomenon of volcanism.

The thickness of the oceanic Earth’s crust is \(8\)—\(10\ \text{km}\). Calculations show that at a depth of \(6\)—\(8\ \text{km}\), with a field strength of \(3 \cdot 10^5\) V/m, which corresponds to the electrostatic strength of porous dielectrics at high temperatures, the number of breakdowns reaches 1,000 per year. Some of them may grow through the full depth of the Earth’s crust [5]. The phenomenon of electric discharges in the atmosphere, which has important

is of practical importance for the life of our planet Earth, and is being studied widely and successfully. Until now, attention has not been paid to the existing gap in the description of the course of geoelectric phenomena, which consists in the following: in the Earth’s atmosphere, which has not very high dielectric properties, there occurs the conversion of forms of energy into electrostatic energy and the electric charging of comparatively large volumes of clouds in the atmosphere, as well as the occurrence of electric discharges. In the Earth’s crust, in the lithosphere, there are also volumes filled with dielectrics with high dielectric properties, higher than in the air atmosphere; however, the possibility of electric discharges occurring in the lithosphere has not been considered. In our hypothesis of discharges in the Earth’s interior, a description of geoelectric phenomena is given and a hypothesis is proposed that eliminates this logical gap. It is shown that discharges in the Earth’s interior can also play a large and varied role in the life of the planet. Discharges in rocks may also be the cause of explosions and fires occurring in mine workings, damage to instruments in electrical prospecting during geological exploration work, the causes of which remain unexplained, and so on.

We conducted experiments on the charging of rocks and observations of discharges in them both in the laboratory and in deep boreholes. These investigations demonstrated the possibility of charging rocks and of the formation of electric discharges in rocks, including in the Earth’s interior, under various charging conditions. Owing to the high strength of rocks in the Earth’s interior, a discharge length of several centimeters was achieved.

The hypothesis considered here, concerning geoelectric phenomena occurring in strong electric fields, appears important for creating a unified scientific description of the processes of transformation of forms of energy and accumulation of electric discharges in the atmosphere and lithosphere. In this way the logical gap in the doctrine of geoelectric processes may be eliminated—a gap that arose because geoelectric processes in the Earth’s interior and in the atmosphere were considered differently, with the loss of continuity and integrity in the description of these processes.

LITERATURE

1. A. A. Vorob'ev. Physical Properties of Matter in the Earth’s Interior. In press.
2. A. A. Vorob'ev. Geology and Geophysics. 1, (1971), No. 12.
3. A. A. Vorob'ev. Electrophysical Apparatus and Electrical Insulation. Moscow, “Energiya,” 1970.
4. Yu. S. Deev et al. Atomic Energy. 29, issue 4, 303, 1970.
5. A. A. Vorob'ev, V. S. Dmitrievskii. Proceedings of Higher Educational Institutions, “Geophysics.” In press.