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Earth electricity: A review of mechanisms which cause telluric currents in the lithosphere

January 2014
Annals of geophysics = Annali di geofisica 56(5):G0564

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Wofford College

Telluric currents are natural electrical phenomena in the Earth or its bodies of water. The strongest electric currents are related to lightning phenomena or space weather. Earth electricity can cause damage to structures, and may be useful for earthquake forecasting and other applications. Thirty-two distinct mechanisms that cause Earth electricity are described, and a broad selection of current research is highlighted. © 2013 by the Istituto Nazionale di Geofisica e Vulcanologia. All rights reserved.

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ANNALS OF GEOPHYSICS, 56, 5, 2013, G0564; doi:10.4401/ag-6184

G0564

Earth electricity: a review of mechanisms which cause telluric

currents in the lithosphere

Daniel S. Helman

California State University Long Beach, Department of Geological Sciences, Long Beach, CA, United States

ABSTRACT

Telluric currents are natural electrical phenomena in the Earth or its bod-

ies of water. The strongest electric currents are related to lightning phe-

nomena or space weather. Earth electricity can cause damage to

structures, and may be useful for earthquake forecasting and other appli-

cations. Thirty-two distinct mechanisms that cause Earth electricity are

described, and a broad selection of current research is highlighted.

1. Introduction

Several phenomena that can generate telluric cur-

rents have been described in scientiﬁc specializations

whose members may not communicate with each

other regularly. The study of this topic is both intrigu-

ing and challenging: Electrical signals do not carry

much of a marker to indicate how they are generated,

beyond magnitude, frequency, and polarization. At-

tenuation and new phenomena caused by transmission

complicate signal characteristics. A wide range of pos-

sible applications for telluric data exists in different

ﬁelds (seismology, hydrology, mineral prospecting,

geothermal prospecting, planetary science, etc.)

For example, seismic electric signals may occur in a pe-

riod leading to increased seismic risk, and understand-

ing the causes of purported seismic electric signals is

critical to characterizing any extant mechanism related

to electricity and earthquake phenomena [Varotsos et

al. 2011]. As another example, dissolved ions in

groundwater increase rock conductivity, and the mo-

tion of the groundwater itself creates an electrical sig-

nal [Corwin and Hoover 1979]. This text is a brief

selection of research in the subject, meant to be a re-

source for further study. Along with artiﬁcial signals,

Earth electrical phenomena are summarized in Table

1, and Table 2 lists telluric currents by frequency, mag-

nitude and signal duration. Thirty-two causes of Earth

electricity are described in the text that follows. Tel-

luric currents were originally deﬁned as natural elec-

tric currents passing through the Earth’s soil or rock

layers or bodies of water, as opposed to its atmosphere.

Artiﬁcial currents were not included. For the purposes

of this paper, any electric current in a planet or on it

may be classed as a telluric current.

2. Space phenomena

2.1. Geomagnetically-induced currents, GIC

The ionosphere is composed of charged particles

and located 85 to 600 km above the Earth’s surface. Elec-

trical phenomena are caused as the solar wind or space

weather impact the ionosphere. The solar wind and

space weather create ionospheric electromagnetic phe-

nomena in the radio spectrum, and these disrupt com-

munication. Eddies in the ionosphere also occur, and

these create electric current in situ, from the motion of

ions. This electric current affects the geomagnetic ﬁeld,

and the resulting geomagnetic anomalies induce telluric

currents in the ground [Boteler et al. 1998]. This is GIC.

Geomagnetically-induced currents cause corrosion in

pipes and pipelines, and are a problem at high latitudes,

where the Earth’s magnetic ﬂux lines point towards (or

away from) the surface of the Earth.

Ore, or other rock bodies, or human-made struc-

tures, such as pipes and cables, respond to electrical

changes in the ionosphere, so that a telluric current is

induced in the ground. Osella et al. [1998], Everett and

Martinec

[

2003], Constable and Constable [2004],

Pulkkinen et al. [2007], and others have studied this

phenomenon. Cycles are related to space weather, and

are dominated by the inﬂuence of the Sun’s eleven-year

sunspot cycle, whose period predicts emissions of gas

from the solar surface. Diurnal variations within this

larger cycle have been recorded [Diodati et al. 2001].

Article history

Received August 9, 2012; accepted June 27, 2013.

Subject classiﬁcation:

Magnetosphere, Magnetic storms, Mineral physics and properties of rocks, Exploration geophysics, Magnetic and electrical

methods, Geology, Space and planetary sciences, Solar-terrestrial interaction.

The ongoing diurnal currents are responsible for the

corrosion of pipelines and cables in some locations, es-

pecially at high latitudes, and have been studied exten-

sively in Scandinavia [Viljanen et al. 2006]. GIC typically

are on the order of 200 amperes (A) in man-made con-

ductors, with durations of approximately 10 seconds

[Kappenman et al. 1981, Viljanen et al. 1999, Pulkkinen

et al. 2008]. The oscillating frequency is typically 0.01

HELMAN

Name Cause Cycle Mechanism

Space Phenomena

GIC

Cosmic Particle Flux

Planetaty Magnetic Field Plasma

Solar

Cosmic

Cosmic Events

(Magnetotail)

11/24hr

Not Known

28d

Electromagnetic Induction

Charge Transmission

Atmospheric Phenomena

TID

Lightning Strikes

Lightning Strikes Induction

Whistler Induction

Whistler Plasma

Volcanic Lightning Strikes

Storm Charging

Atmospheric Disturbavce

Lightning

Volcanic Lightning

Weather

Not Known

Seasonal

Not Known

Seasonal

Electromagnetic Induction

Charge Transmission

Electromagnetic Induction

Charge Transmission

Electrostatic Induction

Oceanic Phenomena

Electrochemical Effects

Ocean Transport Induction

Oceanic Charging

Metabolic Electrochemistry

Ocean Currents

Ocean Electric Currents

Microbes and Algae

Seasonal

Not Known

Charge Transmission

Electromagnetic Induction

Charge Transmission

Surface Phenomena

Artificial Signals

Metabolic Electrochemistry

Exo-Electron Emission

Industry

Microbes and Plants

Primed Material

Various

24hr

Not Known

Electromagnetic Induction

Charge Transmission

Groundwater Phenomena

Electrochemical Effects

Electrokinetic Effects

Seismic Dynamo Induction

Radioactive Ionization

Fluid Flow

Fluid Flow in Porous Media

Seismic waves

Radioactive Decay

Seasonal

Various

Not Known

Charge Transmission

Electrostatic Induction

Charge Transmission

Other Terrestrial Phenomena

Volcanic EM Signals

Seismic EM Signals

Seismic Electric Signals

Fractoemission

Defect Charging

Piezoelectric Effects

Thermoelectric Effects

Pyroelectric Effects

Magma Electrochemistry

Radioactive Emission

Volcanism

Earthquakes

Fracture

Materiale Defects

Crystal Lattice Geometry

Temperature Gradient

Magma Processes

Radioactive Decay

Not Known

Charge Transmission

Domain Rearrangement

Charge Transmission

Domain Rearrangement

Charge Transmission

Deep Terrestrial Phenomena

Geomagnetic Jerk Geodynamo Not Known Electromagnetic Induction

Table 1. Causes and periods of Earth electricity. GIC are geomagnetically induced currents, TID are traveling ionospheric disturbances, and

EM is an abbreviation for the term electromagnetic.

to 0.001 Hz [Price 2002]. Peak current can be on the

order of 2000 A, and these occur about 10 to 100 times

in 100 years [Pulkkinen et al. 2008].

Diurnal ﬂux rates at the sub-auroral latitudes are on

the order of a few millivolts per kilometer (mV km-1)

[Mather et al. 1964]. The strongest oscillation frequency

of these diurnal signals is 0.4 Hz, and is widespread at

different latitudes [Mather et al. 1964]. At high latitudes,

the motion of charged particles also creates a distinct

radio signal, termed the polar chorus, with a charac-

teristic frequency of 300 Hz to 2 kHz [Barr et al. 2000].

Polar chorus is associated with the solar wind, and the

peak intensity is around 50 μV m-1 as recorded from

stations on the ground in Antarctica. It typically exhibits

a diurnal variation [Salvati et al. 2000]. Telluric currents

(and speciﬁcally GIC) were ﬁrst documented in the

1840s with the invention of the telegraph. Buried tele-

graph lines are electrical conductors, and susceptible to

electrical induction. Geomagnetically-induced currents

caused interference during telegraph transmission, so

that the telegraph needles hung frozen by the signals of

the GIC. At ﬁrst this phenomenon was attributed to

weather causes, but it was soon recognized that the

hung needles coincided with the occurrence of aurora

borealis and magnetic storms [Walker 1861].

2.2. Cosmic-particle ﬂux

Direct bombardment by high-energy charged par-

ticles and radiation coming from solar, stellar, and cos-

mic sources, act generally to form GIC. For example, a

gamma-ray ﬂare from a neutron star 23,000 light years

away was reported in 1999 as causing VLF amplitude

changes of more than 20 decibels from interaction with

the ionosphere. The Lyrid, delta-Aquarid and Perseid

metoer showers have caused phase variations in a 16

kHz signal due to GIC [Barr et al. 2000].

For planetary bodies with no atmosphere, this ﬂux

of cosmic particles creates telluric currents directly

[Madey et al. 2002]. Cosmic ray ions have an energy

ﬂux of about 6 × 109eV cm-2 s-1 for bodies in the Solar

System. For Mars, protons and neutrons strike the sur-

face with energy ﬂuxes of around 6000 and 1400 MeV

cm-2, respectively [Molina-Cuberos et al. 2001]. This

process is not occurring on the Earth’s surface at pres-

ent; the atmosphere intervenes.

2.3. Planetary magnetic-ﬁeld plasma

If ultraviolet and X-Ray emissions from a star en-

counter a magnetic ﬁeld, the interactions will create a

plasma of energetic electrons. Such a plasma is created

in the Earth’s magnetosphere from solar radiation, and

strikes the moon’s surface as it passes through the

Earth’s magnetotail. as described in Stubbs et al. [2007].

The magnitude of the charging can be several thousand

volts [Halekas and Fox 2012]. A magnetotail is the dis-

tal part of an oblong magnetic ﬁeld, caused in this case

by the solar wind.

3. Atmospheric phenomena

3.1. Traveling ionospheric disturbances, TID

Atmospheric compression (i.e. acoustic waves) from

a sudden event, such as an earthquake, tsunami, volcanic

eruption, severe weather or rocket launches can create

traveling ionospheric disturbances (TID) [Georges 1968,

Johnston 1997, Afraimovich et al. 2001], and these TID

can induce telluric currents in the ground via the geo-

magnetic ﬁeld. TID are themselves a category of GIC.

The ionosphere also has resonant electrical phe-

nomena, called Schumann resonances, at a fundamen-

tal frequency of 10.6 Hz, with overtones at 18.4, 26.0,

33.5 and 41.1 Hz [Barr et al. 2000]. The background am-

plitude of measured Shumann resonances is about 1.0

picoteslas [Schlegel and Füllekrug 1999]. In addition to

the above examples, TID can form as the result of grav-

ity waves at the troposphere-ionosphere interface

[Georges 1968]. A gravity wave is one where buoyancy

or gravity (or both) act to oppose the displacement. A

common example of a gravity wave is the wind-gener-

ated wave forms one sees at the ocean at the ocean-air

interface. Some TID are akin to these, occurring at the

troposphere-ionosphere interface. No quantitative re-

ports of the magnitudes of telluric currents resulting

from TID are extant, to the best of the author's knowl-

edge, though qualitative magnitudes are known. Space

weather events are the strongest TID, and then, in de-

scending order, daytime signals, atmospheric compres-

sion events, and gravity waves [Georges 1968].

The effect of TID within the ionosphere is for the

disturbance to develop a potential on the order of 1 mil-

livolt per meter [Shiokawa et al. 2003]. Frequency for

the ionospheric dynamo region is modeled to be on the

order of 10-6 to 10-7 Hz [Kaladze et al. 2003]. Higher fre-

quencies are also present [Munro 1958]. Short-term

changes (on the order of hours) to the Earth’s magnetic

ﬁeld may be caused by ionospheric activity. Kaladze et

al. [2003] have modeled ionospheric activity that

matches the magnitude and timing of ground observa-

tions of changes to the geomagnetic ﬁeld.

The ionosphere is studied with dedicated ground-

based facilities, such as the High Frequency Active Au-

roral Research Program (HAARP) and with satellites. A

network of satellites measuring ionospheric distur-

bances are in place. A 1996 space experiment with a

nearly 2 km long conducting line gathered electrical

data in the ionosphere, and then compared these with

EARTH ELECTRICITY: A REVIEW OF MECHANISMS

satellite data. The accuracy of modeled ionospheric ac-

tivity between satellites is low. Modeled electrical data

are off by as much 140% [Szuszczewicz et al. 1998].

On the ground, HAARP has been in operation in

Alaska since 1993 [Bailey and Worthington 1997]. That

facility is designed to transmit radio-frequency electro-

magnetic radiation into the ionosphere for communi-

cation with submarines, with the electrolytes in the

ocean acting as an antenna. HAARP is also suited for

ionospheric studies.

HAARP experiments are designed to study the

structure of the ionosphere, and for determining practi-

cal applications of wave propagation, such as radio sig-

naling. Results have included techniques to produce very

low frequency and extremely low frequency (VLF/ELF

- 30 Hz to 30 kHz) radio waves [Cohen et al. 2008]. Light-

ning channels broadcast electromagnetic radiation in the

VLF range, and HAARP can duplicate this VLF. HAARP

has also been used for magnetotelluric surveying.

In a magnetotelluric survey, both electrical and

magnetic ﬁelds are used for remote sensing, to deter-

mine the electrical resistivity of an area, and variations

within it, according to an empirical equation

(1)

where tis the resistivity in ohm meters (Ω m), f is fre-

quency in Hertz (Hz), E is the electric ﬁeld tensor in

volts per meter (V m-1), and B is the magnetic ﬁeld ten-

sor in nanoteslas (nT) [Wescott and Sentman 2002].

HAARP can generate magnetotelluric signals, and was

used as the transmitter for a proof-of-concept con-

trolled-source audio-magnetotelluric survey (CSAMT)

in Alaska in 1999 and 2000, prospecting for petroleum

[Wescott and Sentman 2002]. This is a new trend. Most

magnetotelluric surveys have historically used natural

ﬁelds [Simpson and Bahr 2005]. Simultaneous meas-

urements of the geomagnetic ﬁeld and of telluric cur-

rents are used to calculate a value for the electrical

impedence at depth, to explore subsurface features.

3.2. Lightning strikes

Electrical charge is transferred between the

ground and the atmosphere during lightning strikes,

and the tops of stormclouds close an electrical circuit

with the ionosphere. Lightning discharge is energetic

and creates plasma that we see. The ﬁrst pulse of light-

ning occurs as charges within the cloud consolidate to

form a strike leader, and plasma from the ground rises

up to meet the leader in that cloud. The next pulse

comes from the cloud to the ground. The process re-

peats, with alternating pulse initiations between

ground and cloud. A lightning strike is a combination

of about 30 pulse events, each lasting nanoseconds,

and its overall duration is on the order of milliseconds

[Uman 1994]. The bulk result is a negative charge given

to the ground. Peak electric current is 99 ± 7 kA, meas-

ured by quantifying remanent magnetization of the

ground and calculating the peak magnetic ﬁeld [Ver-

rier and Rochette 2002]. Oscillation signal frequencies

are on the order of 10-3 MHz to 103MHz, or higher

[Uman and Krider 1982]. The previous data have been

normalized to a 10 km distance, and higher frequency

signals are known to attenuate. With some dry light-

ning and strikes which ignite ﬁres, a positive charge is

given from the cloud to the ground. The magnitude

of charge carried by positive cloud to ground strikes is

increased by the presence of aerosols and smoke

[Nichitiu et al. 2009].

3.3. Lightning-strike induction

Lightning strikes can also cause transient changes

to the geomagnetic ﬁeld [Verrier and Rochette 2002].

Lightning can occur in various weather conditions, in-

cluding thunderstorms, dust storms and tornadoes

[Barr et al. 2000]. Telluric currents arising from this phe-

nomenon ought to have frequencies of 10-3 MHz to 103

MHz, based on the ns to ms variations recorded in

lightning phenomena. These are the same frequencies

that a direct ﬂash of lightning will display. Induction is

localized, and portions of large buildings and towers

are frequently subject to induction when they are

struck. Hussein et al. [2003] compare data from several

structures, and the average magnitudes are between 7

and 12 kA, with peak magnitudes from 20 to 100 kA.

3.4. Whistler induction

Lightning discharge heats the air and creates

plasma. The entire lightning channel radiates electro-

magnetic energy. If in the radio frequency, it is called a

radio atmospheric signal, or sferic. If the plasma from

lightning dishcarge travels along geomagnetic lines, the

resulting radio-frequency disturbances are termed

“whistlers” and are named for the sound which this in-

terference makes in telephone lines, as ﬁrst described in

1919 [Schlatter 2008]. The sound was attributed to light-

ning phenomena in 1953. Whistlers typically occur in

the ELF/VLF range of 3 Hz to 30 kHz [Barr et al. 2000].

For example, observations made from Antarctica at 22.3

kHz show common changes in amplitude of 3 decibels

to an artiﬁcially transmitted signal, with duration of

around 30 seconds. These changes were associated with

whistler activity [Helliwell et al. 1973]. The propogation

of whistlers along geomagnetic ﬂux lines can induce

changes to local magnetic ﬁelds, and these can cause in-

duction of human-made conductors and ore bodies.

HELMAN

1/5 f E/B ,t=2

3.5. Whistler plasma

Whistlers are caused when plasma from lightning

travels along the geomagnetic ﬂux lines. The magni-

tude of the electron density striking the Earth is on the

order of 104electrons per cm3during whistler events

at the equator. Poleward densities should be higher, as

the ﬂux lines there are more inclined to the Earth’s sur-

face [Schlatter 2008].

3.6. Volcanic lightning strikes

An electrical response in the ground as lightning

strikes during volcanic eruptions has been described in

[Aizawa et al. 2010]. They describe magnetotelluric data

from Sakurajima volcano in Kyushu, Japan, from May

2008 to July 2009. Magnetotelluric pulses were recorded

coincident with several strikes.

Generally, volcanic plume heights where volcanic

lightning has been observed are distributed bimodally:

plume heights 1 to 4 km, and plume heights 7 to 12 km.

In the former, volcanic lightning is due to vent

processes, and in the latter volcanic lightning is due to

stratospheric processes [McNutt and Williams 2010].

Occurrence of volcanic lightning increases with height

in the stratospheric plumes, and peak currents greater

than three thousand amperes have been observed [Ben-

nett et al. 2010]. Ash erupted from a volcano is electri-

cally charged. Whether a circuit is made between

charged ash and the ionosphere has not yet been re-

ported. Low frequency (30 kHz to 300 kHz) sferics are

reported, as with meteoroligical lightning events, but

the emission spectra of the ﬂash itself has not been.

Likewise, the author has not found reports of the mag-

nitude of electrical discharge during volcanic lightning.

James et al. [2000] have described a mechanism for

ash charging. In a series of experiments, ash-sized par-

ticles were ground from several crustal rock samples in

a non-conducting sample holder. The materials devel-

oped charges of both polarities, generally based on the

chemical composition of the particles, with the net

charge of ≈10-5 to 10-6 coulombs per kilogram (C kg-1).

Their data are consistent with measurements taken

previously within ash fall plumes [James et al. 2000].

They attribute the charge in the ash to fracture-charg-

ing, also called fractoemission, where electrical charge

is caused in a fracture as electrons are distributed un-

evenly during fracture processes.

Lightning in volcanic plumes is controlled by to-

pography and wind direction, with negative strikes

(negative charge carried to the ground) and positive

strikes (positive charge carried to the ground) evolving

over the course of an eruption [Hoblitt 1994] or occur-

ring simultaneously. The role of water in the magma

and its inﬂuence in volcanic lightning is still an open

question, though the occurrence of volcanic light-

ning is not related to latitude, and, hence, is likely

not related to the ability of the air to hold water

[McNutt and Williams 2010].

3.7. Storm charging

Terrestrial electrical fields occur during storm

activity. A vertical field on the order of 100 V m-1

and a current density at the surface of roughly 2 ×

10-2 A m-2 has been measured during thunderstorm

activity, with water droplet interactions in clouds

perhaps serving as the source of the initial (nega-

tive) charge buildup. These may induce a positive

charge in the ground.

In thunderstorm clouds, the negative charge at

the bottom of the cloud is offset by a positive

charge in the top portion, that together form a con-

ductive circuit flowing upward through the strato-

sphere, also called a thundercloud cell. In reality,

negative charge is flowing downward. The current

has been experimentally determined to be around

0.7 A per thundercloud cell [Troshichev et al. 2004].

Current flow in a thundercloud cell accounts for

about 96% of the electrical activity of a storm,

while lightning discharges account for a minority (≈

4%). Electrical charging of storm clouds is offset by

charging of the ocean surface, where daily electrical

ocean surface variations are consistent with the

daily change of the total area occupied by thunder-

storms [Troshichev et al. 2004]. Electrical frequency

spectra in the ground from electrostatic storm

charging are not reported, to the author's knowl-

edge.

4. Oceanic phenomena

4.1. Electrochemical effects in the ocean

In the oceans, different layers of water will be

stratified by temperature and salinity, and each in-

fluences density. Both of these gradients influence

electrical conductivity, and create variations in elec-

tric currents in the oceans [Chave and Luther 1990].

The signals are low-frequency (30 kHz to 300 kHz)

or lower, typically. Voltages from temperature and

salinity variations in the ocean are less than a few

mV (silver/silver-chloride electrodes were used)

and the differences in salinity and temperature were

less than a few parts per thousand and a few degrees

Celsius, respectively, between electrodes [Larsen

1992]. The electrode material affects the observed

voltage. Internal waves (within the stratified ocean)

are measurable electrically in their vertical compo-

nent as gradients are crossed [Chave 1984].

EARTH ELECTRICITY: A REVIEW OF MECHANISMS

4.2. Ocean transport induction

Electrical induction in the oceans occurs by three

processes: transport of seawater across the geomagnetic

ﬁeld (treated in this subsection); the inﬂuence of GIC

on saltwater, a conductor (treated in the subsections

above dealing with GIC and TID); and variations in sea

water due to variations in salinity and temperature

(treated above.) Bulk water transport was ﬁrst measured

electrically by Faraday in 1832, at the Waterloo Bridge

with electrodes placed in the Thames River, but sunspot

activity (unfortunately) masked the periodic inﬂuence

of the Gulf Stream [Larsen 1992]. Induced voltage due

to transport of saline water has been observed success-

fully, with a magnitude on the order of 25 mV per kilo-

meter, measured on a cable ﬁtted with electrodes in the

Straits of Florida [Larsen 1992]. The GIC (with peaks up

to about 50 mV km-1 but with typical values of 10 to 20

mV km-1) had been subtracted out of the data by hand.

The voltages occur at frequencies from 10-3.8 to 10-7.0

Hz and are incomplete, and tidal variation and other

outliers create peaks around 10-5 Hz.

4.3. Oceanic charging

Two sources of electric currents in the ocean al-

ready described in this text are: storm clouds charging

the ocean surface (above); and processes to charge

water strata in the ocean itself. Electricity from both of

these may be transmitted to the rock with which it is

in contact via electrostatic induction [Cox 1981]. The

oceanic lithosphere receives a quasi-static charge from

the ocean. Due to the high metal content of the rock,

both electrostatic and electromagnetic induction will

occur if major changes to electric current in the oceans

or to the geomagnetic ﬁeld also occur.

4.4. Metabolic electrochemistry in the ocean

The metabolic action of micro- and macrobiota

in the oceans may contribute to an electrical signal that

is measurable. Bohlin et al. [1989] describes how ﬁsh

are attracted to electric signals; this phenomenon

might be related either to physiology or to food sens-

ing. Brahic [2010] describes how an extensive network

of microbial electric currents may exist in oceanic

mud. Atekwana and Slater [2009] introduce the study

of microbial geophysical signatures in a comprehen-

sive manner; biogeophysics is an emerging ﬁeld, and

more research is warranted.

5. Surface phenomena

5.1. Artiﬁcial signals

Earth electric currents may come from the trans-

mission of electricity or electromagnetic radiation em-

anating from human-made sources [Keller 1968, Pham

et al. 1998] and also from on-ground activity, such as

from electric trains. Telluric currents may come from

electrical ﬁelds set up intentionally as, for example,

from a direct-current (DC) electrical ﬁeld designed to

remove contaminants from soils [Probstein and Hicks

1993]. Electroremediation can be accomplished with a

ﬁeld strength of about 150 V m-1. A complexing agent

is added to the groundwater, and contaminants are at-

tracted to wells for removal [Wong et al. 1997].

The magnitude of artiﬁcial telluric currents de-

pends directly upon the generation process. Extremely

low frequency radio waves are generated by heating the

ionosphere, and are used by the US military to commu-

nicate with submarines, for example. Nuclear explosions

above ground also create ionospheric VLF radiation,

with frequencies of 10 kHz to 15 kHz [Barr et al. 2000].

5.2. Metabolic electrochemistry in soil

The daily action of plants, fungi, bacteria, lichen or

algae that inhabit soil and rock ﬁssures may produce

electrical signals from electrochemical processes related

to metabolism. Some evidence exists that soil microbes

respond to changes in the geomagnetic ﬁeld [Jie Li et al.

2009], though the converse has not been shown. Abdel

Aal et al. [2010] report that the imaginary component

of measured conductivity in sand is increased linearly

as Pseudomonas aeruginosa are introduced to the grains.

The imaginary component of conductivity is a measure

of its dissipation, part of the ﬁeld equations that model

oscillating or alternating current. Abdel Aal et al. [2010]

used low frequency (0.1 to 1000 Hz) signals for their

study. No change to the real component of the conduc-

tivity was observed.

Regarding plants: despite the existence of diurnal

electrical variations measured in sapwood [Gilbert et

al. 2006], and in leaves and leaf stems [Gil et al. 2008],

and also despite the invention of functional electrical

circuitry powered by plants and trees [Himes et al. 2010,

Yamaguchi and Hashimoto 2012], no diurnal soil-root

signal from plants has been detected [Love et al. 2008].

A new sensor for these signals has recently been devel-

oped [Gurovich 2009], but no evidence of diurnal sig-

nals has been published yet.

5.3. Exo-electron emission

The process of stress relaxation may release elec-

trons after an initial priming, as can the addition of heat

or photons to a previously stressed sample [Oster et al.

1999]. These and related processes are termed exo-elec-

tron emission if the energy of the electrons is low (less

than or equal to one electron volt), to distinguish it from

high-energy electron emission phenomena, such as frac-

HELMAN

toemission. Exo-electron emission functions by means

of traps and defects and requires a solid-gas or solid-vac-

uum interface for its action: it acts at a surface. Exo-elec-

tron emission may occur in the vadose zone or on the

surface of the crust [Oster et al. 1999, Freund 2011]. Exo-

electron ﬂux is observed as less than or equal to 108elec-

trons (e-) per square centimeter [Oster et al. 1999].

6. Groundwater phenomena

6.1. Electrochemical effects in groundwater

As ionically-charged ﬂuids travel in porous rock, an

electric current is created by the motion of the sus-

pended ions [Corwin and Hoover 1979]. This is the prin-

ciple behind household chemical batteries, and is

common in nature. The electrochemical effect found in

ore bodies, for example, is akin to commercial electro-

chemical batteries in magnitude (a few volts) [Lile 1996].

While the chemistry of the ﬂuid determines the volt-

age, the signal frequencies are controlled by the motion.

6.2. The electrokinetic effect

Just as the motion of ionically-charged ﬂuids in

porous rock creates an electrochemical current, so too

the interaction of the charged ﬂuid with the bounding

rock creates a complementary charging in the rock it-

self. At the ﬂuid-rock interface, a single layer of ad-

sorbed ions attracts a second layer of the opposite sign,

and these are sufﬁcient to create an electrical potential

over a distance. This so-called streaming potential,

caused by an electrokinetic effect, involves electrostatic

induction by moving ions. Self potential is a combina-

tion of streaming potential (based on the electrokinetic

effect) and of the diffusion of the ions themselves.

Typically, self potential is present in groundwa-

ter flows [ Aubert and Atangana 1996, Birch 1998,

Revil et al. 2003, Jardani et al. 2006], but can also be

found in many geologic settings, such as sulphide ore

bodies [Lile 1996] and other mineral deposits, includ-

ing graphitic deposits [Stoll et al. 1995], and on volca-

noes, where the phenomenon is due to hydrothermal

activity, changes in groundwater flow, and magma dis-

placement [Zlotnicki and Nishida 2003]. In hy-

drothermal settings, streaming potential from

electrokinetic effects is much stronger than associated

thermoelectric effects [Corwin and Hoover 1979]. A

streaming potential of up to 30 mV can be generated

from a groundwater change of 50 cm, if the fluid re-

sistivity is 102Ω m and the rock permeability is 10-12

m2[Jouniaux and Pozzi 1995]. Streaming potential

variations occur, with pulses in amplitude of 15 to 40

mV, and a frequency of 0.1 to 0.5 Hz [Jouniaux and

Pozzi 1997].

6.3. Seismic-dynamo induction

Rock is displaced as seismic waves pass through.

Groundwater in the pore space is displaced as well, as

are ions in the groundwater. The motion of ions rela-

tive to the geomagnetic ﬁeld creates circularly or ellipti-

cally polarized electric ﬁelds, with opposite orientations

for positive and negative ions. This effect was reported

in 2009, and was observed both for artiﬁcial seismic

waves from blasting and for natural seismic waves

[Honkura et al. 2009]. The magnitude of the seismic-dy-

namo effect is on the order of μV to mV, and frequency

depends upon the ions in the groundwater, with ob-

served values between approximately 10 and 50 Hz.

Cyclotron frequency is the name given for charged

particles moving in circular motion perpendicular to a

magnetic ﬁeld. Each charged particle has a cyclotron

frequency based on its charge, mass and velocity rela-

tive to the magnetic ﬁeld. The observed seismic-dy-

namo effect reported in Honkura et al. [2009] shows

electric frequencies that may be interpreted as reso-

nances of the cyclotron frequency of particles and the

geomagnetic ﬁeld, with bicarbonate, chloride, sodium

and calcium taken as constituents. These vary in abun-

dance by location, and account for differences of ori-

entation in the observed electric ﬁelds.

6.4. Radioactive ionization

Radionuclides release energy as they decay, and

that energy can ionize surrounding material. Radon gas

is one example. The most common isotope of radon

(222Ra) has a half-life of 3.8 days [Jordan et al. 2011]. Sev-

eral thousand scientiﬁc publications have described the

presence of radon as co-seismic with major events.

Radon at the Earth's surface ionizes particles in the air,

and the motion of these ions creates atmospheric elec-

trical phenomena linking the surface to the ionosphere

[Pulinets 2007]. Co-seismic ionospheric anomalies

might be attributed to the action of ions created as

radon is released. Studies of radon occurrence as an

earthquake precursor often look for radon concentra-

tions in groundwater [Jordan et al. 2011]. It is plausible

to assume that radon ionizes other atoms in ground-

water, and that the motion of these ions can create an

electric signal. Other radionuclides could do the same.

7. Other terrestrial phenomena

7.1. Volcanic electromagnetic signals

Hata et al. [2001] report detection of consistent

electromagnetic signals during the Izu-Miyake volcanic

eruption of 2000 in Japan. The signals preceded the

eruption by a week, and were associated with changes

to the surface of the Earth from magma dike growth.

EARTH ELECTRICITY: A REVIEW OF MECHANISMS

The exact mechanism of the signal generation is un-

known. The observational apparatus was set to detect

extremely low frequency radio waves (between 10 Hz

and 300 Hz). Below 10 Hz, ionospheric and other geo-

magnetic signals predominate, and above 300 Hz, light-

ning noise predominates. The full spectrum of the

occuring radiation is not known.

7.2. Seismic electromagnetic signals

Matsumoto et al. [1998] report television signal in-

terference associated with the 1995 Kobe earthquake in

Japan. The electromagnetic radiation preceded the

earthquake by 6.5 hours, and was characterized as hav-

ing a magnitude of a few tens of mV m-1, a frequency in

the 217 MHz range with microsecond duration. Other

reports of electromagnetic phenomena during earth-

quakes are common, typically involving ionospheric dis-

turbances [Davies and Baker 1965, Pulinets and

Boyarchuk 2004, Popov et al. 2004, Singh and Singh

2007, Pulinets 2007, Perrone et al. 2010, Heki 2011,

Zolotov et al. 2012].

7.3. Seismic electric signals

Three types of signals have been reported from a

network of monitoring stations in Greece [Varotsos et

al. 1993]. First, a gradual variation in the electric ﬁeld of

the Earth (GVEF) has been recorded, on the order of

weeks or more before an earthquake, and with voltage

an order of magnitude higher than other purported pre-

cursory SES. These occur rarely. Second, presumed seis-

mic electric signals, on the order of hours to 11 days

before an earthquake, with an order of magnitude in

the millivolt range, occur commonly. Third, a short du-

ration pulse, 1 to 4 minutes precedent to seismic waves,

with an order of magnitude in the volt range, occur

rarely [Ralshovsky and Komarov 1993, Varotsos et al.

1993]. All three are low-frequency signals, less than or

equal to 1 Hz [Varotsos et al. 2011]. Similar seismic sig-

nal data have been reported in Japan using the same

method [Uyeda et al. 2009].

7.4. Fractoemission

Fractoemission, in which electrons escape from a

freshly cleaved surface, has been described in James et

al. [2000]. Their observations show electrical charging

of about 10-5 coulombs per kilogram for volcanic ash.

Fracture experiments have recorded up to 10 parts per

million (ppm) ozone production from the crushing of

typical terrestrial crustal rock, with the ozone being

generated by electricity from physical charge separa-

tion during fracture [Baragiola et al. 2011] The energy

of the emitted electrons can be very high, up to tens of

thousands of electron volts (10 keV) or higher. The elec-

trons are produced as the surface attains and maintains

a charge, often pulling electrons from deep inside,

termed the Malter effect [Oster et al. 1999]. Electro-

magnetic emission resulting from a single crack in ice

under various stress regimes has a frequency of 103to

105Hz, with a change in potential of about 2 mV

[Shibkov et al. 2005].

7.5. Defect charging

Pressure can cause defects in materials. Defects can

both liberate charge carriers, such as ions or electrons,

and create charge acceptors, such as holes or lattice va-

cancies. Pressure changes can also result in the reorien-

tation and charging of lattice defects, called defect

charging. These processes have characteristic electro-

magnetic emissions, with frequencies in the range 102

to 106Hz for crystals with predominantly ionic bonds

[Shibkov et al. 2005].

Defect charging has been studied as a candidate for

the cause of electrical signals associated with earth-

quake phenomena [Varotsos et al. 1998, Freund 2011].

Takeuchi and Nagao [2013] demonstrate an electro-

motive force of 80 mV in gabbro with 50 MPa of load.

Freund [2011] proposes that peroxy defects present in

silicate rocks, where the tetrahedral silicate bonds are

O3Si-OO-SiO3instead of O3Si-O-SiO3, can be a source

of mobile charge carriers. Peroxy bonds commonly

break under pressure. The new structure can accept an

electron from a neighboring silica-oxygen tetrahedron.

That transfer, in turn, creates a positive hole in the elec-

tron donor. Positive holes can also interact with nega-

tive ions liberated from the lattice by changes in

pressure, e.g. from seismic waves. This condition may

form paths for electric current to ﬂow.

Such defect phenomena are fundamental to how

semiconducting materials work, and are probably wide-

spread in nature. General terms for the process de-

scribed above are "charge-vacancy coupling" or "defect

and charge transport" [Raymond and Smyth 1996]. Per-

oxy bonds exist in silicate rocks in enough numbers to

create measurable electricity. The process of charge-va-

cancy coupling is nontrivial in all rocks, given the right

conditions. Typical electric currents from defect charg-

ing in rock are on the order of 1 nanoampere at 20

megapascals of pressure [Freund 2011].

7.6. The piezoelectric effect

The piezoelectric effect (electric ﬁeld or charge

caused by applied pressure) has been modeled as a crys-

tal lattice effect, as deformation from stress or strain dis-

places the positions of shared electrical bonds [Cady

1946, Mason 1950]. This is the mechanism ﬁrst de-

scribed by Voigt [Voigt 1910, Katzir 2006]. Stress is an

HELMAN

internal pressure of particles acting on each other,

caused by external load. Strain is a change to the shape

of a material, caused by stress. Piezoelectricity is based

on the symmetry of a crystal.

A more in-depth treatment of the ideas in the fol-

lowing paragraph can be found in Sands [1994]. Crys-

tals can have three types of symmetry. If the coordinates

of a crystal lattice are hypothetically reﬂected through

a point, a new inverse lattice with new inverse coordi-

nates is created. If the inverse lattice is identical to the

original crystal lattice, the crystal is centrosymmetric.

If the inverse lattice is not identical to the original crys-

tal lattice, but the inverse lattice can be rotated to match

the original lattice, then the crystal is non-centrosym-

metric. If the inverse lattice is not identical to the origi-

nal crystal lattice, and the inverse lattice cannot be

rotated to match the original lattice, then the crystal is

chiral, also called enantiomorphic. The terms “chiral”

and “enantiomorphic” are synonyms and refer to hand-

edness. These crystals occur in both left-handed and

right-handed forms.

For a more in depth treatment of the following de-

scriptions of piezoelectricity, see Cady [1946]. A cen-

trosymmetric crystal lattice ought not allow for any

electrical charge to build up under pressure. Every bond

displaced will be countered by another bond whose dis-

placement can cancel the charge of the ﬁrst. However,

some minerals with centrosymmetric crystal lattices,

such as zeolites and topaz, express electricity under

stress and strain. No explanation has yet been proposed

for this anomaly.

Many chiral and non-centrosymmetric minerals

display the piezoelectric effect. The most well-known is

quartz, and the most intuitive application at one time

was in record needles or microphones, to change varia-

tions in pressure into an electrical signal. The electrical

signals in these devices are very small, on the order of

10-12 coulombs per newton (C N-1) for a single crystal.

Piezoelectric data for some minerals can be found in

SpringerMaterials, an online version of the Landolt-

Börnstein Database [SPRINGER 2012].

7.7. The thermoelectric effect

A homogeneous conductor expresses a voltage

when there is a temperature gradient, with electrons

(the more negative) at the cold end. This is called the

Seebeck effect (or the thermoelectric effect), and is di-

rectly observable as electric current when two dissimi-

lar conductors are connected to each other under a

thermal gradient [Goupil et al. 2011]. Thermocouples

are based on this effect. For more information on the

following discussion, see von Baeckmann et al. [1997].

Corrosion of bridges and other metal structures where

dissimilar metals are found is caused by this phenome-

non. In the crustal materials of the Earth, the thermo-

electric effect is important in ore bodies, and in regions

with high heat ﬂux. The magnitude is on the order of

10-5 volts per degree Kelvin [SPRINGER 2012].

Geologic case studies are abundant. Shankland

[1975] describes measurements of thermoelectricity

from rock samples in a laboratory setting. Leinov et al.

[2010] describe thermoelectric effects in brine-saturated

sandstone in situ. The thermoelectric effect from ore

minerals, for example from pyrite during computer-

aided resistivity surveys for gold (called pyrite-thermo-

electric surveying), has also been described [Cao Ye et

al. 2008, Zhang Yun-qiang et al. 2010], as has thermo-

electricity from magnetite grains in the Earth’s crust,

and especially in the middle-lower crust [Junfeng Shen

et al. 2010]. This widespread effect is similar to defect

charging (described in the Defect charging subsection,

above) in that both processes mobilize charge carriers

and holes (acceptors), the one with a temperature gra-

dient, the other with pressure.

Note that both of the temperature effects listed in

this section (i.e. the thermo-and pyroelectric effects)

have sometimes been lumped together as the thermo-

electric effect. They have been described as such by Cor-

win and Hoover [1979], who treat temperature effects

as unwanted signal noise in self potential surveying.

They are unwanted if one is looking for electrical indi-

cations of water ﬂow (from the motion of ion-rich

water, and from the electrokinetic effect) for geother-

mal use.

7.8. The pyroelectric effect

Water is a polar molecule. Any material whose

structure has an axis with dissimilar ends, and whose

ends are of uneven electrical charge, is a polar mate-

rial. The dissimilar ends are called a permanent elec-

tric dipole. In polar minerals, electric charges located at

the ends of the permanent electric dipole are rapidly

neutralized by the environment under normal condi-

tions. During heating or cooling, however, the charges

do not have time to dissipate, and are detectable. This

phenomenon is called pyroelectricity, or the pyroelec-

tric effect [Bhalla et al. 1993]. It is sensitive to both the

change in temperature and the rate of change in tem-

perature of a polar material. Tourmalines are common

minerals that exhibit this effect [Hawkins et al. 1995].

Typical magnitudes are on the order of 10-6 coulombs

per square meter per Kelvin for single crystal samples.

7.9. Magma electrochemistry

The motion of magma during volcanic processes

and also of volatiles can hypothetically create an elec-

EARTH ELECTRICITY: A REVIEW OF MECHANISMS

tric signal. Volatiles can in some instances ionize sur-

rounding materials, and magma itself can be rich with

ions. No study of these natural electrical phenomena is

found in the literature, to the author's knowledge. Tora-

maru and Yamauchi [2012], in trying to create an analog

to layered dikes and sills, used an externally applied elec-

tric ﬁeld to create cyclically-layered structure in an arti-

ﬁcial material, PbI2.

7.10. Radioactive emission

Electric current can hypothetically be caused di-

rectly by the motion of charged particles released by

the breakdown of radionuclides. For example, α-parti-

cle emission is a steady source of charged particles, and

therefore creates an electric signal. Signiﬁcant radioac-

tive decay has been reported in natural ﬁssion reactors

as having occurred in the past [Gauthier-Lafaye 1997,

Jensen and Ewing 2001, Stille et al. 2003]. Electrical ob-

servations of this phenomenon are not in the published

literature, to the author’s knowledge.

8. Deep terrestrial phenomena

8.1. Geomagnetic jerk

Short-term changes to the second derivative of the

geomagnetic ﬁeld are termed geomagnetic jerks, and

arise from electrical signals traveling through the man-

tle during deep (core) events [Nagao et al. 2003]. Trans-

mission of electricity from the upper mantle to the

lower crust is likely, but has not been observed. Separate

geomagnetic jerks of limited extent have been modeled

as having been caused by single events originating in and

traveling through Earth’s core, as described in Chulliat

et al. [2009]. The physical models suggest that quantify-

ing mantle conductivity is still an open question [Malin

and Hodder 1982].

The electrical conductivity of the deep mantle is

two orders of magnitude higher than that of the shal-

low mantle, with a transition depth of 670 km. An-

other region of higher conductivity transition occurs

at 2700 km, the D’’ layer, so named as part of Keith

Bullen’s Earth taxonomy from the 1940s [Chao 2000,

Constable and Constable 2004, Duffy 2008, Ohta et al.

2008]. The increased conductivity has been modeled

using a combination of proton conduction if hydrogen

is present and polaron conduction, which is electron

hole hopping between Fe2+ and Fe3+ ions in minerals

that contain iron [Yoshino 2010]. Both of these are

semiconductor phenomena. A wet mantle is not gen-

erally required to ﬁt the observations [Yoshino et al.

2008]. The increase at the D’’ layer is also related to the

transition from perovskite, an orthorhombic mineral,

to post-perovskite, a sheet mineral, that occurs at this

depth [Duffy 2008].

Bulk rock responses to local changes in the geo-

magnetic ﬁeld caused by changes in the Earth’s core

ought to affect ore bodies or other rock with high con-

ductivity. No articles are apparently available that report

long-term telluric currents caused by ﬂuctuations in the

geomagnetic ﬁeld originating in the Earth’s core.

9. Producing electricity

Several models depict electricity-generation

processes. Four of these are useful in conjunction with

the study of telluric currents. These are listed in Table 3,

with a brief explanation for each.

Charged particles, if they change location, transfer

charge. Charged particles, such as electrons or ions, are

termed charge carriers. The motions of ions or electrons

are examples of the direct transfer of electric charge.

A deeper treatment of the ideas in the following de-

scription may be found in Jonassen [2002]. Electrostatic

induction is a special case of charged particle transfer.

An external charge elicits an electrical response from a

second material containing mobile charge carriers. The

charge carriers move to neutralize the applied ﬁeld. If

the external charge is positive, for example, then nega-

tive charge carriers will migrate within the second ma-

terial to the site of the external charge. This model is

termed electrostatic induction because the charge trans-

fer is induced within one of the materials, but no charge

is transferred between them.

A more thorough treatment of the ideas in the fol-

lowing description may be found in Schieber [1986].

Electromagnetic induction occurs in any electrical con-

ductor where a change in a magnetic ﬁeld occurs, so

that the magnetic ﬂux lines pass through the conduc-

tor. The combination of mobile charge carriers and

magnetic ﬂux creates an electromotive force. This is the

principle behind electrical power generation, for exam-

ple. A coil of wire moves through a magnetic ﬁeld, and

the motion creates electric current in the wire. Elec-

tricity is generated.

If the charge carriers in a material are not mobile,

electricity can be generated by deformation of the ma-

terial, or some other process that changes the config-

uration of the domains carrying electric charge. The

rearrangement of electrical domains can generate

electricity.

10. Monitoring telluric currents

The geomagnetic ﬁeld is currently monitored by

an extensive network of government-run observatories

and includes a near-real-time international data reposi-

tory [Kerridge 2001, INTERMAGNET 2012]. The same

is not the case for Earth’s telluric phenomena, but some

HELMAN

EARTH ELECTRICITY: A REVIEW OF MECHANISMS

Model Explanation

Direct Transfer of Charge Charge carriers such as ions or electrons change location, and

their motion transfers electric charge

Electrostatic Induction External electric charge creates an electromotive force within

a material as particles move to neutralize the external charge

Electromagnetic Induction Relative motion of a magnetic ﬁeld creates an electromotive

force on electric charge carriers within it

Rearrangement of Electrical Domains Deformation creates electricity as it changes the position of

immobile charge carriers in a material

Table 3. Electricity-generation models.

Name Magnitude Duration Frequency

Lightning Strikes

Lightning Strike Induction

Volcanic Lightning Strikes

Artificial Signals

GIC (Space Weather)

105A (peak)

105A (peak)/104A

> 3kA (peak)

Various

200 A (metal)

50 μV m-1 (chorus)

Not reported (γ-rays)

Not reported (meteors)

1 ms

Not reported

Various

≈ 10s

Various

10-3 to 103MHz

Not reported

Various

10-3 to 10-2 Hz

300 Hz to 2 kHz

VLF

16 kHz

Planetary Magnetic Field Plasma

Storm Charging

Electrochemical Effetcs

Electrokinetic Effects

Ocean Transport Induction

GIC (Diurnal)

Cosmic Particle Flux

Whistler Plasma

Seismic EM Signals

Fractoemission

Seismic Electric Signals

Seismic Dynamo Induction

Thermoelectric Effects

Pyroelectric Effects

Defect Charging

Exo-Electron Emission

Volcanic EM Signals

TID (Schumann Resonances)

Geomagnetic Jerk

Magma Electrochemistry

Radiaoctive Emission

Radioactive Ionization

5000 V (Lunar surface)

10-2 A m-2

5 V

100 mV km-1

25 mV km-1 (metal)

1 mV km-1 (ionosphere)

6000 MeV cm-2 (Mars)

104 e- cm-3 (surface)

≈ 20 to 50 mV m-1

10-5 C kg-1 (ash)

1 to 10 mV

μV to mV

10-5 V K-1

10-6 C m-2 K-1 (single crystal)

10-9 A

≤ 108e- cm-2

1 to 5 pT

1.0 pT

Not reported

≈ 1 week

hrs to days

Various

Ongoing

≈ 1 d

Various

Not reported

≈ 1 μs

Various

Ongoing

Various

Ongoing

Not reported

< 300 kHz (ocean)

0.1 to 0.5 Hz

Some from 10-7.0 to 10-3.8 hz

0.4 Hz

Not reported

217 MHz

103to 105Hz (ice)

≤ 1 Hz

10 to 50 Hz

Not reported

102to 106Hz

Not reported

Radio frequencies

10.6, 18.4, 26.0, 33.5, and 41.1 Hz

Not reported

Oceanic Charging

TID (Compressive Event)

TID (Gravity Wave)

Whistler Induction

Metabolic Electrochemistry

Not reported

Ongoing

Various

Ongoing

≈ 30 s

Not reported (Hypothetical)

Not reported

10-7 to 10-6 Hz

10 Hz to 30 kHz

Not reported

Table 2. Magnitude, duration and transmission frequency of Earth electricity, arranged by magnitude. GIC are geomagnetically induced

currents, TID are traveling ionospheric disturbances and e- is electrons.

national institutions and systems are in place and usu-

ally produce freely-available data. China, Russia, South

Africa, Japan, Greece, the United States and Canada, for

example, all have networks of magnetotelluric stations

to monitor seismic events as they sometimes correlate

with electrical and magnetic signals. References or web-

sites exist for China [Xuhui Shen et al. 2011], Russia

[ISTP SB RAS 2012], South Africa [Fourie 2011, FACE-

BOOK 2012], Japan [Kawase et al. 1993, Uyeshima et

al. 2001, Geospatial Information Authority of Japan

2010], Greece [Varotsos et al. 1993], and the U.S. and

Canada [Zhdanov et al. 2011, Incorporated Research

Institutions for Seismology 2012]. No global correlation

network of electric signal data exists in real time,

though the MTNet, maintained by a working group of

the International Association of Geomagnetism and

Aeronomy will perhaps assume this role [MTNET

2012]. This association houses research results and data,

acts as an international forum, and hosts workshops

and conferences. Likewise, a working group of the In-

ternational Union of Geodesy and Geophysics (IUGG)

hosts conferences and workshops on Electromagnetic

Studies of Earthquakes and Volcanoes [EMSEV 2013],

and they may have a strong interest in creating this type

of network.

11. Discussion

Thirty-two distinct causes of telluric currents have

been listed above. Here are some highlights that might

serve to promote further research. These have been se-

lected as affecting either public health, the economy, or

human progress.

– Lightning phenomena, GIC, TID and the ther-

moelectric effect are mechanisms that have been of the

greatest interest to society, since these can disrupt com-

munications or destroy structures and equipment. Ex-

cept for lightning, these act via corrosion, and are slow.

– The references to self-potential and the electro-

kinetic effect may deserve more interest, especially the

work out of China, looking at sulﬁde ores and gold.

Rare earth elements also seem to be of strategic eco-

nomic and political importance.

– Seismic electric phenomena may have immense

practical applications for public safety. Distinguishing

between purported seismic electric signals and other

electrical events might allow for successful earthquake

forecasting.

– The papers on using plant metabolism to power

circuits and batteries may be of interest for alternative

energy research. Harnessing plants directly for electric-

ity would attack anthropogenic climate change on two

levels: by providing carbon sequestration and energy

production.

It is hoped that there will be more progress in these

areas, and that Tables 1 and 2 will be critically assessed

and added to. Electrical energy is one of the hallmarks

of life, and of space. It is critical for the transfer of in-

formation, as well. As more of human culture takes ad-

vantage of electronic media, it seems logical and benign

to extend human knowledge of electricity in the Earth

itself. For example, remote sensing is now available for

our homes, and we can turn on lights in a room just by

moving towards it. How much more important is it,

now, to build a more complete system of remote sens-

ing for our global home, the Earth, and its environs?

Missing from this study is a thorough review of

data related to the electrical conductivity of the various

features of the lithosphere, and the connection between

resistivity and rock types, tectonic regimes, seismic ac-

tivity, geochemistry, and similar geologic parameters.

Such a review would likely be fruitful.

Acknowledgements. No funding was received for this proj-

ect, which was completed as part of a Masters thesis on metamor-

phism and electrical phenomena in the Earth’s crust at California

State University Long Beach. Thank you Oleg Zolotov of EMSEV

for constructive criticism related to storm charging, and to

Roswitha Grannell, Andreas Bill, Jack Green and Ewa Burchard of

CSULB for editorial comments. Love always to my parents.

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M. Green (2011). Three-dimensional inversion of

large-scale EarthScope magnetotelluric data based

on the integral equation method: Geoelectrical im-

aging of the Yellostone conductive mantle plume,

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GL046953.

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phological insights of self-potential anomalies on

volcanoes, Surv. Geophys., 24, 291-338.

Zolotov, O.V., A.A. Mangaladze, I.E. Zakharenkova,

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*Corresponding author: Daniel S. Helman,

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email: danielhelmanteaching@yahoo.com.

rights reserved.

EARTH ELECTRICITY: A REVIEW OF MECHANISMS

On the long term drifts in baselines of Ground Magnetic Observatories

Conference Paper

Oct 2014

The stability of baseline is the most important criterions for evaluating the data quality of a ground magnetic observatory. Theoretically, a baseline should be a straight line, provided, there are no error factors affecting the absolute instruments, the variometer and the observational procedure. But in practice, we observe that the baselines are affected by some errors in the form of random errors and long term baseline drifts. It is known that temperature, pier tilts, aging of electronic components etc. can affect the long term stability of baselines, but in this paper we discuss a new type of error which affects the baseline in the form of long term drifts due to the variation in the gradient field between the absolute room and the variometer room. Even though, a site is selected with the least magnetic gradient for the establishment of an observatory, in many cases, it is found that the magnetic gradient patterns are not permanent and changes over the time. This paper deals with the issue of long term baseline instability caused by the temporal changes in the F gradient. We have derived the correction factor which can overcome this problem. Finally we present how far the data quality can be improved by applying this correction.

Electro telluric resonance logging

Article

Full-text available

Dec 2018

Electro telluric resonance logging (ETR-Logging) uses the naturally-occurring electric currents flowing through the rock strata within the body of the Earth to obtain information in regard with the electrical structure of the rock layers. An orthogonal configuration of ground antenna oriented NS and WE and the corresponding electronic circuitry are used for capturing the telluric signals. The position of the logging point is located at the centre of the orthogonal ground antenna. Deep bore holes are not required. The workings of the ETR-Logging follow the principle of the resonance between two signals and the skin-depth effects. The operating mechanisms of the ETR-Logging also conform with the Ohm's Law. A stratum with high resistivity characteristics, such as a saturated oil-bearing formation, gives high amplitude of resonance response and a wide range of phase angle variation of telluric energy. A stratum with low resistivity characteristics such as saline-water-filled sands, gives low amplitude resonance response and wide range phase angle variation. ETR-Logging at three locations in North Kalimantan and one location South Kalimantan, demonstrate the results of this technique. It is effective in predicting the present and the abundance of the deposits as well as verifying the quality of the seals.

Fracture Electric Field: A Synthetic Model for Seismogenic Process and its Relationship with Preseismic Electric Anomalies and Earthquakes

Preprint

Full-text available

Jul 2020

Unobservability of the seismogenic process in a causative fault that makes earthquake (EQ) prediction difficult. Although the relationship between the preseismic electric anomaly (PSEA) and the mainshock indicates that both the PSEA and EQ may originate from same course proceeding in the seismogenic zone, as evidenced by experiments on stressed granite, geological interpretation of those observations, and experiments was limited by the traditional granite formation theory. Based on new information from studies of granite genesis and geotransects, we present a synthetic model, the fracture electric field (FEF), to elucidate the seismogenic process on a causative fault and its logical linkage with the PSEA and EQ. The model is constrained with various data from the 1975 Haicheng EQ and verified by survey data from an FEF monitor station constructed in 2012 in Guangzhou, China. The main conclusions are as follows: (1) An uneven or undulant fault-plane is the prerequisite for stress-accumulation in the locality of the plane to form a seismogenic zone; (2) The position of the continental seismic layer corresponds to that of the crustal granite layer, suggesting that the seismogenic process of any causative fault in continents may produce the PSEA; (3) A normal FEF exists in a causative fault and can be measured beyond the preseismic situation. Thus, it is possible to detect the seismogenic process of a fracture through monitoring the variation of its FEF when the fracture enters a preseismic situation.

Challenges in coupling atmospheric electricity with biological systems

Article

Full-text available

Jul 2020

The atmosphere is host to a complex electric environment, ranging from a global electric circuit generating fluctuating atmospheric electric fields to local lightning strikes and ions. While research on interactions of organisms with their electrical environment is deeply rooted in the aquatic environment, it has hitherto been confined to interactions with local electrical phenomena and organismal perception of electric fields. However, there is emerging evidence of coupling between large- and small-scale atmospheric electrical phenomena and various biological processes in terrestrial environments that even appear to be tied to continental waters. Here, we synthesize our current understanding of this connectivity, discussing how atmospheric electricity can affect various levels of biological organization across multiple ecosystems. We identify opportunities for research, highlighting its complexity and interdisciplinary nature and draw attention to both conceptual and technical challenges lying ahead of our future understanding of the relationship between atmospheric electricity and the organization and functioning of biological systems.

Possible Tectonic Impact of Biosphere

Preprint

Full-text available

Sep 2019

Eugene Bagashov

This paper explores the possibility of existence of ultra-deep biosphere (deeper than 10 km under the surface) and the biogenic earthquake hypothesis -- the idea that subsurface microorganisms might be directly related to earthquake activity. The importance of electroautotrophic type of metabolism is underlined, and the role of telluric currents in this process is explored in some detail, as well as the role of subsurface and atmospheric microorganisms in the global electric circuit.It seems that the existing estimates of the adaptability of biological organisms are inconsistent with empirical evidence, and theoretical concepts predict key biochemical processes to fail long before the onset of the temperatures and pressures, at which microorganisms are actually observed. This implies that life might exist much deeper beneath the surface than previously assumed. At the same time the estimates of energy radiated during the strongest earthquakes are consistent with the biochemical energy available to the subsurface biosphere.Some additional evidence is examined. It is proposed that the ultra-deep biosphere might represent an important factor in resolving the debate on the nature of hydrocarbons. At the same time the deep subsurface microorganisms might play a significant evolutionary role, not only providing seismically induced genetic variation and a "seed bank" for quick recovery after a mass extinction, but also by modulating longer climatic cycles through planetary-wide bio-geo-electrochemistry.

Exploratory Study On The Natural Ground Electric Current That Flows Through Human Body As A Possible Pathway For The Therapeutic Effects Of Beach Going

Article

Full-text available

Sep 2018
COMPLEMENT THER MED

Seong Lee Neoh

This paper explores the electrical nature of sandy beach and proposes a pathway for the therapeutic effects of beach going. The electric potential and current generated on the ground across the human body and resistors were measured. The ground was found to have a non-homogenous electric potential which generated a potential difference between any two points on the ground. A power curve, similar to a battery, in the nanowatt range was obtained. This power appeared to be stable across time but varies across ground location. Standing on the beach with dry feet did not allow any current in the micro-ampere range to conduct. But upon moistening the feet, the body electrical resistance was reduced by 94% and the ground potential difference across the two feet was sufficient to drive a micro-ampere range current through the body. This may be one reason for the therapeutic effects of being on the beach.

Long term drifts in baselines of Ground Magnetic Observatories.

Article

Feb 2017

The stability of baseline is the most important criterion for evaluating the data quality of a ground magnetic observatory. Theoretically, a baseline should be a straight line, provided, there are no error factors affecting the absolute instruments, the variometer and the observational procedure. But in practice, we observe that the baselines are affected by some errors in the form of random errors and long term baseline drifts. It is known that temperature, pier tilts, aging of electronic components, etc. can affect the long term stability of baselines, but in this paper we discuss a new type of error which affects the baseline in the form of long term drifts due to the variation in the gradient field between the absolute room and the variometer room. Even though, a site is selected with the least magnetic gradient for the establishment of an observatory, in many cases, it is found that the magnetic gradient patterns are not permanent and changes over the time. This slow gradient changes can distort the actual temporal magnetic variations and thus affecting the purity of data recorded at a geomagnetic observatory. We have analytically shown that an ideal baseline has to be a horizontal straight line and the RHS of the fundamental equation of an observatory should be a constant. We have further shown that baseline instabilities are caused by variation in gradient field between the absolute and variometer pillars in addition to the measurement errors from absolute observations and variometer recording. This variation in the gradient field causes long term drifts in baselines. We have derived the correction factor which can filter out the signals arising out of variation in the gradient field. Finally we present how far the data quality can be improved by applying this correction.

Identification de Précurseurs de Séismes Majeurs. Le rôle des orages géomagnétiques

Conference Paper

Full-text available

Mar 2015

Depuis la fin des années 1980 des recherches ont été initiées sur l’identification de signaux précurseurs de séismes. Mais ce n’est que depuis quelques années que l’on commence à les identifier plus clairement. Dans une première partie, une synthèse est présentée sur les principales techniques utilisées pour définir des précurseurs. La seconde partie est centrée sur les effets potentiels d’orages géomagnétiques dans le déclenchement de tremblements de Terre. Elle fait appel à plusieurs disciplines scientifiques. Une nouvelle piste de recherche est proposée.

Magnetic Methods, Principles

Chapter

May 2021

Kusumita Arora

Modelling of ULF Pc4 - Pc5 Pulsations with solar winds and geomagnetic storm for ULF earthquake precursor

Article

Oct 2023
ADV SPACE RES

Operational Earthquake Forecasting: State of Knowledge and Guidelines for Utilization

Article

Full-text available

Aug 2011
ANN GEOPHYS-ITALY

Following the 2009 L'Aquila earthquake, the Dipartimento della Protezione Civile Italiana (DPC), appointed an International Commission on Earthquake Forecasting for Civil Protection (ICEF) to report on the current state of knowledge of short-term prediction and forecasting of tectonic earthquakes and indicate guidelines for utilization of possible forerunners of large earthquakes to drive civil protection actions, including the use of probabilistic seismic hazard analysis in the wake of a large earthquake. The ICEF reviewed research on earthquake prediction and forecasting, drawing from developments in seismically active regions worldwide. A prediction is defined as a deterministic statement that a future earthquake will or will not occur in a particular geographic region, time window, and magnitude range, whereas a forecast gives a probability (greater than zero but less than one) that such an event will occur. Earthquake predictability, the degree to which the future occurrence of earthquakes can be determined from the observable behavior of earthquake systems, is poorly understood. This lack of understanding is reflected in the inability to reliably predict large earthquakes in seismically active regions on short time scales. Most proposed prediction methods rely on the concept of a diagnostic precursor; i.e., some kind of signal observable before earthquakes that indicates with high probability the location, time, and magnitude of an impending event. Precursor methods reviewed here include changes in strain rates, seismic wave speeds, and electrical conductivity; variations of radon concentrations in groundwater, soil, and air; fluctuations in groundwater levels; electromagnetic variations near and above Earth's surface; thermal anomalies; anomalous animal behavior; and seismicity patterns. The search for diagnostic precursors has not yet produced a successful short-term prediction scheme. Therefore, this report focuses on operational earthquake forecasting as the principle means for gathering and disseminating authoritative information about time-dependent seismic hazards to help communities prepare for potentially destructive earthquakes. On short time scales of days and weeks, earthquake sequences show clustering in space and time, as indicated by the aftershocks triggered by large events. Statistical descriptions of clustering explain many features observed in seismicity catalogs, and they can be used to construct forecasts that indicate how earthquake probabilities change over the short term. Properly applied, short-term forecasts have operational utility; for example, in anticipating aftershocks that follow large earthquakes. Although the value of long-term forecasts for ensuring seismic safety is clear, the interpretation of short-term forecasts is problematic, because earthquake probabilities may vary over orders of magnitude but typically remain low in an absolute sense (< 1% per day). Translating such low-probability forecasts into effective decision-making is a difficult challenge. Reports on the current utilization operational forecasting in earthquake risk management were compiled for six countries with high seismic risk: China, Greece, Italy, Japan, Russia, United States. Long-term models are currently the most important forecasting tools for civil protection against earthquake damage, because they guide earthquake safety provisions of building codes, performance-based seismic design, and other risk-reducing engineering practices, such as retrofitting to correct design flaws in older buildings. Short-term forecastingof aftershocks is practiced by several countries among those surveyed, but operational earthquake forecasting has not been fully implemented (i.e., regularly updated and on a national scale) in any of them. Based on the experience accumulated in seismically active regions, the ICEF has provided to DPC a set of recommendations on the utilization of operational forecasting in Italy, which may also be useful in other countries. The public should be provided with open sources of information about the short-term probabilities of future earthquakes that are authoritative, scientific, consistent, and timely. Advisories should be based on operationally qualified, regularly updated seismicity forecasting systems that have been rigorously reviewed and updated by experts in the creation, delivery, and utility of earthquake information. The quality of all operational models should be evaluated for reliability and skill by retrospective testing, and they should be under continuous prospective testing against established long-term forecasts and alternative time-dependent models. Alert procedures should be standardized to facilitate decisions at different levels of government and among the public. Earthquake probability thresholds should be established to guide alert levels based on objective analysis of costs and benefits, as well as the less tangible aspects of value-of-information, such as gains in psychological preparedness and resilience. The principles of effective public communication established by social science research should be applied to the delivery of seismic hazard information.

The electrical response of fruit trees to soil water availability and diurnal light-dark cycles

Article

Full-text available

Oct 2008
Plant Signal Behav

Recent studies have associated the effect of water stress, irrigation, and light cycles with electrical signaling in fruit tree species including avocado, blueberry, lemon and olive. In those studies, changes in the electrical potential (EP) difference were detected between the base of the stem and leaf in response to drought, irrigation, and diurnal changes in light and dark. In avocado, the changes in EP between the base of the stem and leaf petiole (ΔVL-S) observed in response to decreased soil water content have been associated with a decrease in stomatal conductance, indicating that stomatal closure might be associated with an electrical signal. New experiments were conducted to determine the effects of short- and long-term drought on root to leaf electrical signaling in avocado confirming that in both situations significant changes in EP differences can be detected and that an extra-cellular electrical signal appears to be involved in root to leaf communication initiating stomatal closure. Day-to-night fluctuations in EP observed in fruit trees appeared to correspond to the time of day and were therefore presumably affected by diurnal changes in ambient light and vapor pressure deficit.

The science and technology train: A support for geoscience training, research and service delivery in South Africa

Article

Full-text available

Jan 2012

Stoffel C.J. S. Fourie

Plans are well advanced for converting disused railway carriages into travelling science classrooms, laboratories, and an exhibition centre in the form of a Science and Technology (S&T) Train that will travel to the deep rural areas of South Africa. This multimillion rand educational resource will focus initially on promoting the geosciences and their applications, providing onboard expertise in teaching and in the conduct of research, supported by the necessary technical equipment and the experts on board. It is also intended to reach out to and create science awareness among the young and their parents who live on its route; for undergraduate and postgraduate training; as a source of advice on social services; as a contributor to economic development; and as an adjunct to international research programmes. The S&T Train is also to be a vehicle for training first-degree students at technical universities in particular, allowing them to obtain the experiential learning that is a prerequisite for them to graduate. Also featuring on the train’s agenda is problem-solving associated with rural daily life, such as the provision of clean drinking water, the search for sources of local building materials and assistance with appropriate placement of waste sites. Redundant rolling stock donated by Transnet Freight Rail is currently being refurbished for its new role, and the project will be managed by the Tshwane Institute for Advanced Studies at Tshwane University of Technology in Pretoria, with support from the Department of Science and Technology and other government departments.

Electromagnetic Induction Phenomena

Book

Jan 1986

David Schieber

On magnetic storms and Earthcurrents

Article

C.V. Walker

Research on the typomorphisms of compositions and thermoelectric characteristics of pyrite from zhaodaoshan gold geposit in the eastern shandong province

Article

Sep 2010

Pyrite is one of the most important gold bearing minerals in eastern Shandong gold province. The compositions,crystal form,thermoelectric characteristics and cell parameters and so on were studied to unravel the mechanism of hydrothermal gold deposits. It was showed that the composition of pyrite is characterized by poor in S, rich in As. The typical trace elements same as other places in the eastern Shandong province are comprised by As, Co, Ni, Mo, Se, Au, Ag, Sb, Pb and Te. Average contents of trace elements in pyrites of different mineralizing stages indicated that the crystallizing temperature gradually became low from the early stage to the main metallogenic stages, and the precipitation and concentration of Au occurred during quartz-pyrite stage and polymetal minerals stage. The electric conduct assemblage for the pyrite is characterized by P>N →P<N→-P N→P N, from stage I toV. Gold minerals are closely related to As in the pyrite and the P/(P+N) value and the electric conduct assemblage are closely correlated to the composition of As and (Co+Ni). Based on the crystallizing temperature of pyrite, the changes of thermoelectrical coefficient with depth, the distribution of pyrite type and the mean of thermoelectric coefficient , it is considered that the genesis of Zhaodaoshan gold deposit belongs to the hydrothermal gold ore deposit of middle-low temperature. The denudation rate is lower and the deep part of ore body has not been exhumed until now. The higher region of the value of a p and P% often indicates the rich ore segment. By means of pyrite-thermoelectricity mapping, it shows that there are two high-value areas of ap and P% below 200 m level from line 8 to line 16 and near the line 120. It is suggest that good exploring prospect of the two favorable positions of gold mineralization are proposed on the basis of above study.

Application of thermoelectric properties of pyrite in gold exploration in the Shihu gold deposit, western Hebei

Article

Aug 2008

This paper introduces the application of the pyrite thermoelectric property measurements in gold exploration of the Shihu gold deposit. Pyrite is the main gold-carrying mineral. Four gold mineralization stages may be distinguished. The thermoelectric type assemblage of pyrite is P<N⇒P≥N⇒P>N⇒P≤N from mineralization stages I to IV. In the mineralization area, from the top downward when (P and P% decrease, (N and N% increase, which in the main coincides with the results of mineralogical mapping by using the distribution of pyrite type (P%) and the mean of the thermoelectric coefficient (P. Some typomorphic information such as formation temperatures of pyrite, relative burial depths of orebodies, characteristics of orebodies and prospects of the deep part may be obtained according to thermoelectric properties of pyrite.

The Kluwer International Series in Engineering and Computer Science

Chapter

Jan 1996

To correlate gas adsorption equilibria data many different adsorption isotherms (AIs) are used in today’s literature [1, 2], To extend their range of applicability often characteristic exponents αi ≠ 1 of Freundlich type are introduced. However, in this case the limiting slope of the AI at low pressure is either infinite or zero, contrary to experimental data of adsorption equilibria indicating a finite nonzero slope. The object of this work is to overcome this difficulty by introducing pressure (and temperature) dependent exponents to ensure the existence of the classical Henry region. Using these exponents in the classical Langmuir-Freundlich AI, it is possible to correlate experimental adsorption data in a wide range of pressure and temperature. The temperature dependences of other parameters in a class of generalized Langmuir-Freundlich AIs is also discussed.

Ionospheric Precursors of Earthquakes

Book

Jan 2004

The book aims to explain the variations of near-Earth plasma observed over seismically active areas several days/hours before strong seismic shocks. It demonstrates how seismo-ionospheric coupling is part of the global electric circuit and shows that the anomalous electric field appearing in active seismic areas is the main carrier of information from the earth into the ionosphere. The discussion of physical mechanisms is based on experimental data. The results can be regarded as the basis for future applications such as short-term earthquake prediction. It proceeds to describe existing complex systems of space-born and ground-based monitoring for electromagnetic and ionospheric precursors of earthquakes, as well as those still under construction. It is an excellent text for courses and contains a wealth of information for those scientists working in the field of natural disaster reduction. © Springer-Verlag Berlin Heidelberg 2004. All rights are reserved.

Real-Time Plant Water Potential Assessment Based on Electrical Signalling In Higher Plants

Conference Paper

Jan 2009

Luis A Gurovich

Real - time plant water potential assessment is postulated as an efficient tool for irrigation scheduling and automated irrigation system operation in precision agriculture. We have developed an Ag/AgCl micro-electrode enabling the continuous measurement of plant electric potential differences between roots, shoots and leaves, in response to changes in micro - environmental conditions related to light, temperature and soil water availability. Electric action (EAP) and variation (EVP) potentials have been detected in several plant organs; most EAP ranged -50 to -250 mV, and lasted from a few miliseconds up to 1 minute, with a very short lag time after the stimuli is imposed. In most cases, AP were followed by long term (1 to 10 hours) distinct EVP. Our results indicate that there is a clear, fast and accurate electrical signalling mechanism within the plant, which is positively correlated to the intensity and duration of micro-environmental stimuli modifying plant water potential. In several fruit trees, placed in a Faraday cage in an environmentally-controlled greenhouse, changes in EP between the base of the stem and leaf petiole (ΔV L-s) observed in response to short-and long-term drought, have been associated with a decrease in stomata conductance (gs), indicating that stomata closure might be associated with an extra-cellular electrical signal, that travels through the phloem at a speed of 2.4 cm min-1. In our experiments, the onset of irrigation (watering) has been associated with changes in EP in avocado, blueberry, lemon and olive. Even greater changes in ΔVL-s have been detected in response to drought as compared to watering; these drought-induced electrical signals were also related to changes in gs. Applications of this signalling mechanism as an early detector of plant water stress are discussed and many questions with regard to the role of electrical signals in eliciting physiological responses in fruit tree species are proposed.

Earth electricity: A review of mechanisms which cause telluric currents in the lithosphere

Abstract

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