ANNALS OF GEOPHYSICS, 56, 5, 2013, G0564; doi:10.4401/ag-6184
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
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.
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. , Everett and
2003], Constable and Constable ,
Pulkkinen et al. , 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].
Received August 9, 2012; accepted June 27, 2013.
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
Name Cause Cycle Mechanism
Cosmic Particle Flux
Planetaty Magnetic Field Plasma
Lightning Strikes Induction
Volcanic Lightning Strikes
Ocean Transport Induction
Ocean Electric Currents
Microbes and Algae
Microbes and Plants
Seismic Dynamo Induction
Fluid Flow in Porous Media
Other Terrestrial Phenomena
Volcanic EM Signals
Seismic EM Signals
Seismic Electric Signals
Crystal Lattice Geometry
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. .
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.  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
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
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.  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.
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.  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-
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.  describes how ﬁsh
are attracted to electric signals; this phenomenon
might be related either to physiology or to food sens-
ing. Brahic  describes how an extensive network
of microbial electric currents may exist in oceanic
mud. Atekwana and Slater  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.  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. 
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-
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
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.  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.  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.  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].
Fractoemission, in which electrons escape from a
freshly cleaved surface, has been described in James et
al. . 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  demonstrate an electro-
motive force of 80 mV in gabbro with 50 MPa of load.
Freund  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
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 . 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
For a more in depth treatment of the following de-
scriptions of piezoelectricity, see Cady . 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. .
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
 describes measurements of thermoelectricity
from rock samples in a laboratory setting. Leinov et al.
 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 , 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-
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 , 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. . 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 . 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 .
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
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
EARTH ELECTRICITY: A REVIEW OF MECHANISMS
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 Strike Induction
Volcanic Lightning Strikes
GIC (Space Weather)
> 3kA (peak)
200 A (metal)
50 μV m-1 (chorus)
Not reported (γ-rays)
Not reported (meteors)
10-3 to 103MHz
10-3 to 103MHz
10-3 to 10-2 Hz
300 Hz to 2 kHz
Planetary Magnetic Field Plasma
Ocean Transport Induction
Cosmic Particle Flux
Seismic EM Signals
Seismic Electric Signals
Seismic Dynamo Induction
Volcanic EM Signals
TID (Schumann Resonances)
5000 V (Lunar surface)
10-2 A m-2
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)
≤ 108e- cm-2
1 to 5 pT
≈ 1 week
hrs to days
≈ 1 d
≈ 1 μs
< 300 kHz (ocean)
0.1 to 0.5 Hz
Some from 10-7.0 to 10-3.8 hz
103to 105Hz (ice)
≤ 1 Hz
10 to 50 Hz
10.6, 18.4, 26.0, 33.5, and 41.1 Hz
TID (Compressive Event)
TID (Gravity Wave)
≈ 30 s
Not reported (Hypothetical)
10-7 to 10-6 Hz
10 Hz to 30 kHz
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
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
– 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
– 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
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
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*Corresponding author: Daniel S. Helman,
California State University Long Beach, Department of Geological
Sciences, Long Beach, CA, United States;
© 2013 by the Istituto Nazionale di Geoﬁsica e Vulcanologia. All
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