ISSN 1990�7931, Russian Journal of Physical Chemistry B, 2013, Vol. 7, No. 5, pp. 589–593. © Pleiades Publishing, Ltd., 2013.Original Russian Text © A.A. Namgaladze, 2013, published in Khimicheskaya Fizika, 2013, Vol. 32, No. 9, pp. 9–13.

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INTRODUCTION

According to well�established concepts [1–26], theglobal electric circuit (GEC) consists of the highlyconducting Earth and ionosphere and the poorly con�ducting (but still conducting due to ionization by cos�mic rays and radioactive gases) air space between them(atmosphere), through which weak electric currentsflows, connecting the circuit sections with high conduc�tivity. These currents are directed upwards in areas ofthunderstorm activity, from the Earth to the thunder�clouds and further to the ionosphere, and downwards,from the ionosphere to the Earth in other places, so�called fair weather currents (figure). Thunderstorm cur�rents charge the ionosphere positively relative to theEarth and create a potential difference between the Earthand the ionosphere of about (250 ± 50) kV. The total cur�rent in the circuit is about 1 kA. The density of fairweather currents is usually ~2–3 pA/m2. The densityof thunderstorm currents is higher (10–1000 pA/m2)as many times as the area of thunderstorm activityareas is smaller than that of fair weather, varying sub�

stantially from place to place (depending on the orog�raphy, such currents are more intense over moun�tains). Magnetospheric currents represent the outersection of the GEC, coupled with the ionosphere bymeans of so�called field�aligned (along the geomag�netic field) currents, with a density of the order of frac�tions µA/m2, which create an ionospheric electricfield across the polar caps with a potential difference of30–150 kV between their morning and evening edges.

The aforementioned GEC currents are consideredto be reliably detected. Besides these, there are ideasabout so�called hypothetical seismogenic electric fieldsand currents associated with earthquakes and processesof their preparation, which give rise to various effects inthe Earth’s ionosphere. It is these currents and theirionospheric effects with emphasis on the effects thatmanifest themselves before, not after or during earth�quakes, will be discussed in the present article. Also tobe considered is whether there are GEC disturbancesprior to an earthquake, which could be interpreted asearthquake precursors of and used for prognosis.

Earthquakes and Global Electrical CircuitA. A. Namgaladze

Murmansk State Technical University, Murmansk, Russiae�mail: namgaladze@yandex.ru

Received November 15, 2012

Abstract—Based on recent experimental and theoretical model results, the role of earthquakes and processesof their preparation as electricity sources in the global electric circuit (GEC) is discussed. In addition to thetraditional elements of the GEC, such as thunderstorm currents, ionosphere currents, fair weather currents,and telluric currents, hypothetical seismogenic currents flowing between the faults and the ionosphere areconsidered. The ionization sources for these currents are presumably the radiation of radioactive gases andthe ionization by the electric field of so�called “positive holes” created by the compression of tectonic plates,whereas transportation of electric charges between the Earth and the ionosphere occurs under the action ofelectric fields and turbulent diffusion (for heavy charged species). Seismogenic currents deliver electriccharges into the ionosphere, which give rise to electric fields in it and in the magnetically conjugated region.The drift of magnetized plasma in the ionosphere F2�region and plasmasphere plasma under the action ofthese fields causes disturbances in the electron density and total electron content (TEC) of the ionosphere,which are observed by GPS satellites before strong earthquakes. The typical features of these disturbances(magnitudes, dimensions, stability, nighttime predominance of the relative TEC disturbances, geomagneticconjugacy) are well reproduced in theoretical model calculations based on the solution of the equation for theelectric ionosphere potential with specified seismogenic electric current at the lower boundary of the iono�sphere if this current is strong enough (comparable with thunderstorm currents). The feasibility of such seis�mogenic currents is discussed. It is argued that the TEC disturbances observed before strong earthquakes can�not be explained by neutral atmosphere disturbances. These TEC disturbances can be treated as ionosphericearthquake precursors created by seismogenic GEC disturbances.

Keywords: earthquake, global electric circuit, ionosphere, epicenter, seismogenic electric fields and currents,total electron content, tectonic fault, mathematical simulation

DOI: 10.1134/S1990793113050229

CHEMICAL PHYSICS OF ATMOSPHERIC PHENOMENA

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IONOSPHERIC PRECURSORS TO EARTHQUAKES: OBSERVATIONS

The search for earthquake precursors in iono�spheric and magnetic data has been going on for along time in different frequency bands, with positiveresults, although the forecast of earthquakesremains out of reach. In recent years, thanks to thedevelopment of global navigation satellites (GPS,GLONASS), earthquake precursors are commonlysought for using data on the total electron content(TEC) of the ionosphere obtained with a much higherspatial and temporal resolution than conventionalion�probe data.

An analysis of works on earthquake precursors inthe TEC [27–40] makes it possible to formulate thefollowing set of their manifestations:

(1) relative (defined as percentages with respect tothe undisturbed background values) TEC disturbances(increase (more often) or decrease) are as high as sev�eral tens of percent;

(2) cover an area of about ~1000 × 3000 km (lati�tude × longitude);

(3) persist for 4–10 h or longer;

(4) maintain their shape (isolines in maps) and donot move during the time of existence;

(5) are attached to the epicenter region and often toregions magnetically conjugated with it, but are notstrictly identical to them (occur nearby);

(6) exist mainly during nighttime, being weakened,until complete disappearance upon arrival of themorning terminator, and renewed with the arrival ofthe evening terminator;

(7) change the shape of the F2�region anomaly inthe equatorial ionosphere.

IONOSPHERIC PRECURSORS TO EARTHQUAKES: THE PHYSICAL

INTERPRETATION AND MATHEMATICAL MODELING

The literature discusses two main mechanisms ofseismic�ionospheric coupling: hydrodynamic andelectromagnetic. The first involves the transmission ofseismic effects into the ionosphere through hydrody�namic disturbances of the neutral atmosphere, morespecifically, internal gravity waves. The second mecha�nism considers an electromagnetic seismic�ionosphericcoupling by means of so�called hypothetical seis�mogenic electric fields and currents associated withearthquakes and the processes of their preparation.

The first mechanism is obviously unsuitable toexplain the above properties of the ionospheric TECdisturbances before strong earthquakes, since neutralatmosphere disturbances cannot be localized(“locked”) near the epicenter. They will propagatefrom the source with known characteristics of travel�ing ionospheric disturbances caused by large�scaleinternal gravity waves. The horizontal velocity of suchperturbations is ~700 m/s, whereas the oscillationperiods range of from ~30 min to ~3 h [41]. These fea�tures are absent in stable large�scale ionospheric TECdisturbances observed before strong earthquakes,which are localized near the epicenter and often nearthe magnetically conjugated region.

The electromagnetic mechanism presumes thatseismogenic�origin electric fields influence the iono�sphere. The author of the present paper elaborated onthis influence [42], by explaining it by the transporta�tion of a magnetized ionospheric plasma in the F2�region by the electromagnetic [ЕВ]�drift in crossedelectric (Е) and magnetic (В) fields. The upward verti�cal component of the drift, created by the zonal elec�tric field directed to the east, transfers plasma to alti�tudes with a low concentration of N2 and О2 mole�cules, a factor that slows down the loss of О+ ions(dominant in the F2�region) in the ion–moleculereactions with N2 and О2 molecules and leads to anincrease in the electron density and TEC relative to theundisturbed state. The downward drift of plasmacaused by the electric field directed to the west, on thecontrary, transfers (lowers) plasma into a region with ahigh content of molecules and with high losses of О+

ions, which leads to a decrease in the electron concen�tration and TEC relative their values in the undisturbedstate. The meridional and zonal (along the parallel)components of the drift redistribute the electron densityperturbation and TEC produced by vertical drift alonghorizontal directions.

The model calculations performed in [43–49] haveshown that the formation of the observed perturba�tions of TEC through this mechanism requires electricfields in the ionosphere of the order of a few mV/m.However, it is necessary to understand how these fields

Ionospherehigh conductivity

Atmospherelow conductivity

Groundhigh conductivity

j � 2–3 pА/m2j � 10–100 pА/m2

j � 1000 pА/m2

Thunderstorms Fair weather regions

Scheme of the global electric circuit.

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EARTHQUAKES AND GLOBAL ELECTRICAL CIRCUIT 591

are generated and how the mechanisms of their gener�ation are related to seismic activity.

It is clear that the primary source of these fieldsmust be some kind of processes near tectonic faultsinvolving the generation of electric charges, i.e., theionization of neutral atoms and molecules. Further,these charges must be delivered to the ionosphere,where they would create a so�called seismogenic elec�tric field.

In the literature, two possible sources of air ioniza�tion near the tectonic faults are considered: by(1) radiation from radioactive elements, primarilyradon emitted from the faults [50–55] and (2) theelectric field produced by the accumulation of so�called “positive holes” near the boundaries of faults,which are created by the compression of rocks duringthe collision of tectonic plates [56–62].

Electrons arising during ionization (free andattached to heavy species) and positive ions can movedifferently in the vertical direction, depending on thebalance of forces acting on them. These forces are cre�ated by the electric fields (background field, directedfrom the ionosphere to the Earth, and the field of pos�itive holes, directed oppositely) and the pressure gra�dients that provide turbulent transport of heavy spe�cies, such as aerosols, water vapor, etc. The resultingcharge transport, an electric current, can generally bedirected upwards, into the ionosphere, or downwards,toward the ground, creating in the ionosphere fields ofopposite signs (the background electric field and theturbulent transport of negatively charged heavy speciesproduce a downward current, whereas the near�ground field of “positive holes”, an upward current).

What should be the strength of the vertical currentsflowing between the ionosphere and the Earth thatthey would be able to create electric fields in the iono�sphere of the order of several mV/m, required to pro�duce measurable TEC perturbations? The answer tothis question is provided by a number of studies [47–49, 63–69], in which the equation for the potential ofthe ionospheric electric field with variable�intensityvertical currents at the lower boundary of the iono�sphere was solved. The density of these currents mustbe at least not less, if not greater, than the density oflightning currents, i.e., 1–10 nA/m2, which is 1000–10000 times higher than the fair weather current den�sity. The total current over the faults must not be lessthan the total current in the GEC, i.e., less than 1 kA.

Are there any such current values in reality?According to [70–72], yes, there are. However, unlikethe situation with the TEC, their relation to seismicactivity remains unproved due to the lack of directmeasurements of currents, rather than their magnetic�ionospheric effects, at specific places and times ofearthquake preparation, which, alas, are unknown inadvance. Thus, variations of the ionospheric TECderived from navigation satellites observations with a

high spatial and temporal resolution, are today themain contender for the position of data capable ofproviding information on ionospheric precursors ofpreparing earthquakes.

CONCLUSIONS

TEC variations observed before strong earthquakesof the ionosphere cannot be explained by anythingother than the influence of electric fields. Unlike per�turbations of neutral atmosphere, quasistationaryelectric fields can be “attached” to their source andthe magnetically conjugated region (due to a high con�ductivity of geomagnetic field lines). In this case, theequality of the electric fields at both ends of the geo�magnetic field line does not mean identity of theeffects they create in the electron concentration andTEC because of differences of the background states ofthe ionosphere and neutral atmosphere in the differenthemispheres. This explains the magnetic conjugationof TEC perturbations and their asymmetry withrespect to the geomagnetic equator.

The ionospheric effects of the electric fields signif�icantly weaken during the daytime because of the con�ductivity of the illuminated ionosphere is higher thanthat of the nighttime ionosphere. This explains thepredominant occurrence of relative TEC perturba�tions in the evening, which disappear in the morning.

The structure of seismogenic origin electric fields issuch that, just above the source, the field changes itsdirection (as the field of a point charge), so TEC per�turbations should be located not exactly above thesource, but nearby, as is observed. The equatorialanomaly of the F2�region is primarily controlled by anelectric field, so that its variations before earthquakesare indicate of electric field perturbations.

Lastly, seismogenic perturbations of the electrondensity in the ionosphere give rise to disturbances inthe variations of magnetic fields and electromagneticradiation in various bands through perturbations ofcurrents and refraction indices for electromagneticwaves, thereby creating ensembles of earthquake pre�cursors of electromagnetic origin. The electric currentbetween the tectonic fault and the ionosphere requiredfor creating such disturbances should be comparableto or even exceed the thunderstorm current, so that therole of seismogenic currents in the global electric cir�cuit is no less important than the role of thunderstormelectricity.

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Translated by V. Smirnov