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

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

Abstract

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.
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
2
Name Cause Cycle Mechanism
Space Phenomena
GIC
Cosmic Particle Flux
Planetaty Magnetic Field Plasma
Solar
Cosmic
Cosmic Events
(Magnetotail)
11/24hr
Not Known
Not Known
28d
Electromagnetic Induction
Charge Transmission
Charge Transmission
Atmospheric Phenomena
TID
Lightning Strikes
Lightning Strikes Induction
Whistler Induction
Whistler Plasma
Volcanic Lightning Strikes
Storm Charging
Atmospheric Disturbavce
Lightning
Lightning
Lightning
Lightning
Volcanic Lightning
Weather
Not Known
Seasonal
Seasonal
Seasonal
Seasonal
Not Known
Seasonal
Electromagnetic Induction
Charge Transmission
Electromagnetic Induction
Electromagnetic Induction
Charge Transmission
Charge Transmission
Electrostatic Induction
Oceanic Phenomena
Electrochemical Effects
Ocean Transport Induction
Oceanic Charging
Metabolic Electrochemistry
Ocean Currents
Ocean Currents
Ocean Electric Currents
Microbes and Algae
Seasonal
Seasonal
Seasonal
Not Known
Charge Transmission
Electromagnetic Induction
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
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
Not Known
Charge Transmission
Electrostatic Induction
Charge Transmission
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
Earthquakes
Fracture
Materiale Defects
Crystal Lattice Geometry
Temperature Gradient
Temperature Gradient
Magma Processes
Radioactive Decay
Not Known
Not Known
Not Known
Not Known
Not Known
Not Known
Not Known
Not Known
Not Known
Not Known
Not Known
Not Known
Not Known
Charge Transmission
Charge Transmission
Domain Rearrangement
Charge Transmission
Domain Rearrangement
Charge Transmission
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.
3
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
4
1/5 f E/B ,t=2
6
@
5
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
6
7
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
8
9
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
10
11
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
1 ms
Not reported
Various
10s
Various
Various
Various
10-3 to 103MHz
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
Not reported
Not reported
Not reported
1 week
hrs to days
Various
Ongoing
Ongoing
1 d
Various
Not reported
1 μs
Various
Various
Various
Ongoing
Ongoing
Various
Various
Various
Ongoing
Ongoing
Ongoing
Not reported
Not reported
Not reported
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
Not reported
217 MHz
103to 105Hz (ice)
1 Hz
10 to 50 Hz
Not reported
Not reported
102to 106Hz
Not reported
Radio frequencies
10.6, 18.4, 26.0, 33.5, and 41.1 Hz
Not reported
Not reported
Not reported
Not reported
Oceanic Charging
TID (Compressive Event)
TID (Gravity Wave)
Whistler Induction
Metabolic Electrochemistry
Not reported
Not reported
Not reported
Not reported
Not reported
Ongoing
Various
Ongoing
30 s
Not reported (Hypothetical)
Not reported
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.
References
Abdel Aal, G.Z., E.A. Atekwana, S. Rossbach and D.D.
Werkema (2010). Sensitivity of geolelectrical meas-
urements to the presence of bacteria in porous
media, J. Geophys. Res., 115, G03017; doi:10.1029/
2009JG001279.
Afraimovich, E.L., E.A. Kosogorov, N.P. Perevalova and
A.V. Plotnikov (2001). The parameters of shock
acoustic waves generated during rocket launches,
Adv. Space Res., 27, 1339-1343.
Aizawa, K., A. Yokoo, W. Kanda, Y. Ogawa and M. Iguchi
(2010). Magnetotelluric pulses generated by vol-
canic lightning at Sakurajima volcano, Japan, Geo-
phys. Res. Lett., 37, L17301; doi:10.1029/2010GL04
4208.
Atekwana, E.A., and L.D. Slater (2009). Biogeophysics:
A new frontier in Earth science research, Rev. Geo-
phys., 47, RG4004; doi:10.1029/2009RG000285.
Aubert, M., and Q.Y. Atangana (1996). Self-potential
method in hydrogeological exploration of volcanic
areas, Ground Water, 34, 1010-1016.
Bailey, P.G., and N.C. Worthington (1997). History and
application of HAARP technologies: The High Fre-
quency Active Auroral Research Program in Pro-
ceedings, Intersociety Energy Conversion Engineer-
ing Conference, IECEC-97, 32nd, (2), 1317-1322.
Baragiola, R., C.A. Dukes and D. Hedges (2011). Ozone
HELMAN
12
13
generation by rock fracture: Earthquake early warn-
ing?, Appl. Phys. Lett., 99, 204101; doi:10.1063/1.366
0763.
Barr, R., D. Llanwyn Jones and C.J. Rodger (2000). ELF
and VLF radio waves, J. Atmos. Sol. Terr. Phys., 62,
1689-1718.
Bennett, A.J., P. Odams, D. Edwards and Þ. Arason
(2010). Monitoring of lightning from the April -May
2010 Eyjafjallajökull volcanic eruption using a very
low frequency lightning location network: Environ.
Res. Lett., 5, 044013; doi:10.1088/1748-9326/5/4/04
4013.
Bhalla, A.S., W.R. Cook Jr. and S.T. Liu (1993). Low fre-
quency properties of dielectric crystals: Piezoelec-
tric, pyroelectric and related constants in Landolt-
Börnstein Numerical Data and Functional Rela-
tionships in Science and Technology, New Series,
Group III: Condensed Matter: Crystal and Solid
State Physics, Volume 29b, O. Madelung (editor),
Berlin, Springer-Verlag, 554 pp.
Birch, F.S. (1998). Imaging the water table by filtering
self-potential profiles, Ground Water, 36, 779-782.
Bohlin, T., S. Hamrin, T.G. Heggberget, G. Rasmussen
and S.J. Saltveit (1989). Electrofishing – Theory and
practice with special emphasis on salmonids, Hy-
drobiologia, 173, 9-43.
Boteler, D.H., R.J., Pirjola and H. Neyanlinna (1998).
The effects of geomagnetic disturbances on electri-
cal systems at the Earth’s surface, Adv. Space Res.,
22, 17-27.
Brahic, C. (2010). The real Avatar: Ocean bacteria act
as “superorganism”, New Scientist, 205, 11.
Cady, W.G. (1946). Piezoelectricity: An Introduction to
the Theory and Applications of Electromechanical
Phenomena in Crystals, New York, McGraw-Hill,
822 pp.
Cao Ye, Li Sheng-rong, Ao Chong, Zhang Hua-feng,
Li Zhen-zhen and Liu Ziao-bin (2008). Application
of thermoelectric properties of pyrite in gold ex-
ploration in the Shihu gold deposit, western Hebei,
Geology in China, 04, http://en.cnki.com.cn/Jour
nal_en/A-A011-DIZI-2008-04.htm (May 2012).
Chao, B.F. (2000). Renaming D double prime: Forum:
Eos, Trans. Amer. Geophys. Union, 81, 46.
Chave, A.D. (1984). On the electromagnetic fields in-
duced by oceanic internal waves, J. Geophys. Res.,
89, 10519-10528.
Chave, A.D., and D.S. Luther (1990). Low-frequency,
motionally induced electromagnetic fields in the
ocean, J. Geophys. Res., 95, 7185-7200.
Chulliat, A., E. Thébault and G. Hulot (2009). Core field
acceleration pulse as a common cause of the 2003
and 2007 geomagnetic jerks, Geophys. Res. Lett., 37,
L07301; doi:10.1029/2009GL042019.
Cohen, M.B., U.S. Inan and M.A. Golkowski (2008).
Geometric modulation: A more effective method of
steerable ELF/VLF wave generation with continu-
ous HF heating of the lower ionosphere, Geophys.
Res. Lett., 35, L12101; doi:10.1029/2008GL034061.
Constable, S., and C. Constable (2004). Observing ge-
omagnetic induction in magnetic satellite meas-
urements and associated implications for mantle
conductivity, Geochem. Geophys. Geosyst. 5,
Q01006; doi:10.1029/2003GC000634.
Corwin, R.F., and D.B. Hoover (1979). The self-poten-
tial method in geothermal exploration, Geophysics,
44, 226-245.
Cox, C.S. (1981). On the electrical conductivity of the
oceanic lithosphere, Phys. Earth Planet. In., 25, 196-
201.
Davies, K., and D. Baker (1965). Ionospheric effects ob-
served around the time of the Alaskan earthquake
of March 28, 1964, J. Geophys. Res., 70, 2251-2253.
Diodati, P., S. Piazza, A. Del Sole and L. Masciovecchio
(2001). Daily and annual electromagnetic noise vari-
ation and acoustic emission revealed on the Gran
Sasso mountain, Earth Planet. Sci. Lett., 184, 719-724.
Duffy, T.S. (2008) Mineralogy at the extremes, Nature,
451, 269-270.
EMSEV (2013). IUGG, http://www.emsev-iugg.org/em
sev/ (December 2013).
Everett, M.E., and Z. Martinec (2003). Spatiotemporal
response of a conducting sphere under simulated
geomagnetic storm conditions, Phys. Earth Planet.
In., 138, 163-181.
FACEBOOK (2012). Permanent Long Period Magne-
totelluric (MT) Network, https://www.facebook.
com/pages/Permanent-Long-Period-Magnetotellu
luric-MT-Network/158145917612101 (October 2012).
Fourie, C.J.S. (2011). The science and technology train:
A support for geoscience training, research and
service delivery in South Africa, S. Afr. J. Geol., 114,
585-592.
Freund, F. (2011). Pre-earthquake signals: Underlying
physical processes: J. Asian Earth Sci., 41, 383-400.
Gauthier-Lafaye, F. (1997). The last natural nuclear fis-
sion reactor, Nature, 387, 337.
Georges, H.F. (1968). HF Doppler studies of traveling
ionospheric disturbances, J. Atmos. Terr. Phys., 30,
735 -736, IN5 -IN8, 737-746.
Geospatial Information Authority of Japan (2010). Data
download – MT (Magnetotellurics) data, http://vldb.
gsi.go.jp/sokuchi/geomag/menu_03/mt_data-e.
html (October 2012).
Gil, P.M., L. Gurovich and B. Schaffer (2008). The elec-
trical response of fruit trees to soil water availability
EARTH ELECTRICITY: A REVIEW OF MECHANISMS
and diurnal light-dark cycles, Plant Signal. Behav., 3,
1026-1029.
Gilbert, D., J.-L. Le Mouël, L. Lambs, F. Nicollin and F.
Perrier (2006). Sap flow and daily electric potential
variations in a tree trunk, Plant Sci., 171, 572-584.
Goupil, C., W. Seifert, K. Zabrocki, E. Müller and G.J.
Snyder (2011). Thermodynamics of thermoelectric
phenomena and applications, Entropy, 13, 1481-
1517.
Gurovich, L.A. (2009). Real-time plant water potential
assessment based on electrical signalling in higher
plants, In: Proceedings World Congress on Com-
puters in Agriculture, 7th, (Reno, Nevada, June 22-24),
The American Society of Agricultural and Biological
Engineers, 095875, https://elibrary.asabe.org/ ( June
2013).
Halekas, J., and K. Fox (2012). Why does the Earth’s
magnetotail cause lightning on the moon?, http://
www.quora.com/Heliophysics/Why-does-the-
Earths-magnetotail-cause-lightning-on-the-moon
(June 2012).
Hata, M., I. Takumi and H. Yasukawa (2001). Electro-
magnetic-wave radiation due to diastrophism of
magma dike growth in Izu-Miyake volcanic eruptions
in Japan in 2000, Nat. Hazard. Earth Sys., 1, 43-51.
Hawkins, K.D., I.D.R. MacKinnon and H. Schneeberger
(1995). Influence of chemistry on the pyroelectric
effect in tourmaline, Am. Mineral., 80, 491-501.
Heki, K. (2011). Ionospheric electron enhancement pre-
ceding the 2011 Tohoku-Oki earthquake, Geophys.
Res. Lett., 38, L17312; doi:10.1029/2011GL047908.
Helliwell, R.A., J.P. Katsufrakis and M.L. Trimpi (1973).
Whistler-induced amplitude perturbation in VLF
propagation, J. Geophys. Res., 78, 4679-4688.
Himes, C., E. Carlson, R.J. Ricchiuti, B.P. Otis and B.A.
Parviz (2010). Ultralow voltage nanoelectronics
powered directly, and solely, from a tree, IEEE
Trans. Nanotechnol., 9, 2-5.
Hoblitt, R.P. (1994). An experiment to detect and locate
lightning associated with eruptions of Redoubt Vol-
cano, J. Volcanol. Geotherm. Res., 62, 499-517.
Honkura, Y., Y. Ogawa, M. Matsushima, S. Nagaoka,
N. Ujihara and T. Yamawaki (2009). A model for ob-
served circular polarized electric fields coincident
with the passage of large seismic waves, J. Geophys.
Res.: Solid Earth, 114, B10103; doi:10.1029/2008JB0
06117.
Hussein, A.M., W. Janischwskyj, M. Milewski, V. Shostak,
F. Rachidi and J.S. Chang (2003). Comparison of cur-
rent characteristics of lightning strokes measured at
the CN Tower and at other elevated objects, In: Pro-
ceedings IEEE International Symposium on Elec-
tromagnetic Compatibility (August 18-22), 495-500.
Incorporated Research Institutions for Seismology
(2012). USArray – Magnetotelluric Array, http://
www.usarray.org/researchers/obs/magnetotelluric
(October 2012).
INTERMAGNET (2012). What is INTERMAGNET?,
http://www.intermagnet.org/ (March 2012).
ISTP SB RAS (2012). Observatories: Institute of Solar-
Terrestrial Physics, Russian Academy of Sciences,
Siberian Branch, http://en.iszf.irk.ru/Observatories
(October 2012).
James, M.R., S.J. Lane and J.S. Gilbert (2000). Volcanic
plume electrification: Experimental investigation of
a fracture-charging mechanism, J. Geophys. Res.,
105, 16,641-16,649.
Jardani, A., J.P. Dupont and A. Revil (2006). Self-poten-
tial signals associated with preferential groundwa-
ter flow pathways in sinkholes, J. Geophys. Res.,
111, B09204; doi:10.1029/2005JB004231.
Jardani, A., A. Revil, A. Bolève and J.P. Dupont (2008).
Three-dimensional inversion of self-potential data
used to constrain the pattern of groundwater flow
in geothermal fields, J. Geophys. Res., 113, B09204;
doi:10.1029/2007JB005302.
Jensen, K.A., and R.C. Ewing (2001). The Okélobondo
natural fission reactor, southeast Gabon: Geology,
mineralogy, and retardation of nuclear-reaction
products, Geol. Soc. Am. Bull., 113, 32-62.
Jie Li,Yan-li Yi, Zhong-ke He, Xi-lei Cheng, Da-geng
Zhang and Yun-bo Fang (2009). Effects of magnetic
treatment on some soil microbial activities in brown
earth, Chinese Journal of Soil Science; doi:CNKI:
SUN:TRTB.0.2009-06-010.
Johnston, M.J.S. (1997). Review of electric and magnetic
fields accompanying seismic and volcanic activity,
Surv. Geophys., 18, 441 -476.
Jonassen, N. (2002). Electrostatics: Berlin, Springer, The
Springer International Series in Engineering and
Computer Science, 700, 188 pp.
Jordan, T., Y. Chen, P. Gasparini, R. Madariaga, I. Main,
W. Marzocchi, G. Papadopoulos, G. Sobolev, K.
Yamaoka and J. Zschau (2011). OPERATIONAL
EARTHQUAKE FORECASTING. State of Knowl-
edge and Guidelines for Utilization, Annals of Geo-
physics, 54 (4); doi:10.4401/ag-5350.
Jouniaux, L., and J.P. Pozzi (1995). Streaming potential
and permeability of saturated sandstones under tri-
axial stress: Consequences for electrotelluric anom-
alies prior to earthquakes, J. Geophys. Res.: Solid
Earth, 100, 10197-10209.
Jouniaux, L., and J.P. Pozzi (1997). Laboratory meas-
urements anomalous 0.1-0.5 Hz streaming potential
under geochemical changes: Implications for elec-
trotelluric precursors to earthquakes, J. Geophys.
HELMAN
14
15
Res.: Solid Earth, 102, 15335-15343.
Junfeng Shen, Xuhui Shen, Qian Liu and Na Ying
(2010). The themo-electric effect of magnetite and
the mechanism of geo-electric abnormalities during
earthquakes, Geosci. Frontiers, 1, 99-104.
Kaladze, T.D., O.A. Pokhotelov, R.Z. Sagdeev, L. Sten-
flo and P.K. Shukla (2003). Planetary electromag-
netic waves in the ionospheric E-layer, J. Atmos. Sol.
Terr. Phys., 65, 757-764.
Kappenman, J.G., V.D. Albertson and N. Mohan (1981).
Current transformer and relay performance in the
presence of geomagnetically-induced currents, IEEE
Transactions on Power Apparatus and Systems,
PAS-100, 1078-1088.
Katzir, S. (2006). The Beginnings of Piezoelectricity: A
Study in Mundane Physics, Dordrecht, The Nether-
lands, Springer, Boston Studies in Philosophy of Sci-
ence, 246, 300 pp.
Kawase, T., S. Uyeda, M. Uyeshima and M. Kinoshita
(1993). Possible correlation between geoelectric po-
tential change in Izu-Oshima Island and the earth-
quake swarm off the east Izu Peninsula, Japan,
Tectonophysics, 224, 83-93.
Keller, G.V. (1968). Statistical study of electric fields from
Earth-return tests in the western states compared
with natural electric fields, IEEE Transactions on
Power Apparatus and Systems, PAS-87, 1050-1057.
Kerridge, D. (2001). INTERMAGNET: Worldwide
near-real-time geomagnetic observatory data, In:
Proceedings of European Space Agency’s Space
Weather Workshops, ESTEC 3rd (Noordwijk, The
Netherlands, December 17-19); http://esa-space
weather.net/spweather/workshops/SPW_W3/
PROCEEDINGS_W3/index.html (March 2012).
Larsen, J.C. (1992). Transport and heat flux of the
Florida Current at 27 degrees N derived from cross-
stream voltages and profiling data: theory and ob-
servations, Phil. Trans. Phys. Sci. Eng., 338, 169-236.
Leinov, E., J. Vinogradov and M.D. Jackson (2010).
Salinity dependence of the thermoelectric coupling
coefficient in brine-saturated sandstones, Geophys.
Res. Lett., 37, L23308; doi:10.1029/2010GL045379.
Lile, O.B. (1996). Self potential anomaly over a sulphide
conductor tested for use as a current source, J. Appl.
Geophys., 36, 97-104.
Love, C.J., Shuguang Zhang and A. Mershin (2008).
Source of sustained voltage difference between the
xylem of a potted Ficus benjamina tree and its soil,
PLOS One, 3, e2963; doi:10.1371/journal.pone.000
2963.
Madey, T.E., R.E. Johnson and T.M. Orlando (2002).
Far-out surface science: Radiation-induced surface
processes in the solar system, Surf. Sci., 500, 838-858.
Malin, S.R.C. and B.M. Hodder (1982). Was the 1970
geomagnetic jerk of internal or external origin?,
Nature, 296, 726-728.
Mason, W.P. (1950). Piezoelectric Crystals and Their
Application to Ultrasonics, New York, D. Van Nos-
trand Company, Inc., 508 pp.
Mather, K.B., E.J. Gauss and G.R. Cresswell (1964). Di-
urnal variations in the power spectrum and polar-
ization of telluric currents at conjugate points, L=2.6,
Aust. J. Phys., 17, 340-388.
Matsumoto, H., M. Ikeya and C. Yamanaka (1998).
Analysis of barber-pole color and speckle noises
recorded 6 and a half hours before the Kobe earth-
quake, Jpn. J. Appl. Phys., 37, L1409-L1411.
McNutt, S.R., and E.R. Williams (2010). Volcanic light-
ning: Global observations and constraints on source
mechanisms, Bull. Volcanol., 72, 1153-1167.
Molina-Cuberos, G.J., W. Stumptner, H. Lammer, N.I.
Kömle and K. O’Brien (2001). Cosmic ray and UV
radiation models on the ancient Martian surface,
Icarus, 154, 216-222.
MTNET (2012). MTNet, http://mtnet.dias.ie/main/
(October 2012).
Munro, G.H. (1958). Travelling ionospheric distur-
bances in the F region, Aust. J. Phys., 11, 91-112.
Nagao, H., T. Iyemori, T. Higuchi and T. Araki (2003).
Lower mantle conductivity anomalies estimated
from geomagnetic jerks, J. Geophys. Res., 108, 2254;
doi:10.1029/2002JB001786.
Nichitiu, F., J.R. Drummond, J. Kar and J. Zou (2009).
An extreme CO pollution event over Indonesia meas-
ured by the MOPITT instrument, Atmos. Chem.
Phys. Discuss., 9, 1211-1233.
Ohta, K., S. Onoda, K. Hirose, R. Sinmyo, K. Shimizu,
N. Sata, Y. Ohishi and A. Yasuhara (2008). The elec-
trical conductivity of post-perovskite in Earth’s D’’
layer, Science, 320, 89-91.
Osella, A., A. Favetto and E. López (1998). Currents in-
duced by geomagnetic storms on buried pipelines as
a cause of corrosion, J. Appl. Geophys., 38, 219-233.
Oster, L., V. Yaskolko and J. Haddad (1999). Classifica-
tion of exoelectron emission mechanisms, Phys.
Status Solidi, 174, 431-439.
Perrone, L., L.P. Korsonova and A. Mikhailov (2010).
Ionospheric precursors for crustal earthquakes in
Italy, Annales Geophysicae, 28, 941-950.
Pham, V.N., D. Boyer, G. Chouliaras, J.L. Le Mouël, J.C.
Rossignol and G.N. Stavrakakis (1998). Characteris-
tics of electromagnetic noise in the Ioannina region
(Greece): A possible origin for so called “Seismic Elec-
tric Signal” (SES), Geophys. Res. Lett., 25, 2229-2232.
Popov, K.V., V.A. Liperovsky, C.V. Meister, P.F. Biagi,
E.V. Liperovskaya and A.S. Silina (2004). On ionos-
EARTH ELECTRICITY: A REVIEW OF MECHANISMS
pheric presursors of earthquakes in scales of 2-3 h,
Phys. Chem. Earth, 29, 529-535.
Price, P.R. (2002). Geomagnetically induced current ef-
fects on transformers, IEEE Trans. Power Del., 17,
1002-1008.
Probstein, R.F., and R.E. Hicks (1993). Removal of con-
taminants from soils by electric fields, Science, 260,
498-503.
Pulinets, S.A., and K.A. Boyarchuk (2004). Ionospheric
Precursors of Earthquakes, Berlin, Springer, 289 pp.
Pulinets, S.A. (2007). Natural radioactivity, earthquakes,
and the ionosphere, Eos, Trans. Amer. Geophys.
Union, 88, 217-219.
Pulkkinen, A., R. Pirjola and A. Viljanen (2007). Deter-
mination of ground conductivity and system pa-
rameters for optimal modeling of geomagnetically
induced current flow in technologyical systems,
Earth Planets Space, 59, 999-1006.
Pulkkinen, A., R. Pirjola and A. Viljanen (2008). Statis-
tics of extreme geomagnetically induced current
events, Space Weather, 6, S07001, doi:10.1029/2008
SW000388.
Ralshovsky, T.M., and L.N. Komarov (1993). SES activ-
ity and the Earth’s electric potential, Tectono-
physics, 224, 95-101.
Raymond, M.V., and D.M. Smyth (1996). Defects and
charge transport in perovskite ferroelectrics, J. Phys.
Chem. Solids, 57, 1507-1511.
Revil, A., V. Naudet, J. Nouzaret, and M. Pessel (2003).
Principles of electrography applied to self-potential
electrokinetic sources and hydrogeological applica-
tions, Water Resour. Res., 39, 1114; doi:10.1029/20
01WR000916.
Salvati, M.A., U.S. Inan, T.J. Rosenberg and A.T. Weath-
erwax, (2000). Solar wind control of polar chorus,
Geophys. Res. Lett., 27, 649-652.
Sands, D.E. (1994). Introduction to Crystallography:
New York, Dover Publications, 192 pp.
Schieber, D. (1986). Electromagnetic Induction Phe-
nomena, Berlin, Springer, Springer Series in Elec-
tronics and Photonics, 16, 312 pp.
Schlatter, N. (2008). Whistlers: Discovering the plasma-
pause, http://www.staff.alfvenlab.kth.se/nickolay.
ivchenko/teach/pro08/proj1.pdf ( July 2012).
Schlegel, K., and M. Füllekrug (1999). Schumann reso-
nance parameter changes during high-energy parti-
cle precipitation: J. Geophys. Res., 104, 10111-10118.
Shankland, T.J. (1975). Electrical conduction in rocks
and minerals: Parameters for interpretation, Phys.
Earth Planet. In., 10, 209-219.
Shibkov, A.A., M.A. Zheltov, V.V. Skvortsov, R.Y.
Kol’tsov and A.V. Shuklinov (2005). Electromagnetic
emission under uniaxial compression of ice: I. Iden-
tification of nonstationary processes of structural
relaxation by electromagnetic signals, Crystallogr.
Rep., 50, 994-1004.
Shiokawa, K., Y. Otsuka, C. Ihara, T. Ogawa and F.J.
Rich (2003). Ground and satellite observations of
nighttime medium-scale traveling ionospheric dis-
turbance at midlatitude: J. Geophys. Res.: Space,
108, 2156-2202.
Simpson, F. and K. Bahr (2005). Practical Magnetotel-
lurics: Cambridge, Cambridge University Press,
272 pp.
Singh, C., and O.P. Singh (2007). Simultaneous ionos-
pheric E- and F-layer perturbations caused by some
major earthquakes in India, Annales Geophysicae,
50, 111-122.
SPRINGER (2012). SpringerMaterials The Landolt-
Börnstein Database, http://www.springermaterials.
com/docs/index.html (May 2012).
Stille, P., F. Guathier-Lafaye, K.A. Jensen, S. Salah, G.
Bracke, R.C. Ewing, D. Louvat and D. Million (2003).
REE mobility in groundwater proximate to the nat-
ural fission reactor at Bangombé (Gabon), Chem.
Geol., 198, 289-304.
Stoll, J., J. Bigalke and E.W. Grabner (1995). Electro-
chemical modelling of self-potential anomalies,
Surv. Geophys., 16, 107-120.
Stubbs, T.J., J.S. Halekas, W.M. Farrell and R.R. Vondrak
(2007). Lunar surface charging: A global perspective
using lunar prospector data, In: H. Krueger and A.
Graps (eds.), Workshop on Dust in Planetary Sys-
tems (September 26-30, 2005, Kauai, Hawaii), ESA
SP-643, 181-184.
Szuszczewics, E.P., P. Blanchard, P. Wilkinson, G. Crow-
ley, T. Fuller-Rowell, P. Richards, M. Abdu, T. Bullett,
R. Hanbaba, J.P. Lebreton, M. Lester, M. Lockwood,
G. Millward, M. Wild, S. Pulinets, B.M. Reddy, I.
Stanislawska, G. Vannaroni and B. Zolesi (1998). The
first real-time worldwide ionospheric predictions
network: An advance in support of spaceborne ex-
perimentation, on-line model validation, and space
weather, Geophys. Res. Lett., 25, 449-452.
Takeuchi, A., and T. Nagao (2013). Activation of hole
charge carriers and generation of electromotive
force in gabbro blocks subjected to nonuniform
loading, J. Geophys. Res.: Solid Earth, 118, 915-925.
Toramaru, A., and S. Yamauchi (2012). Effect of per-
meable flow on cyclic layering in solidifying magma
bodies: Insights from an analog experiment of dif-
fusion-precipitation, In: European Geosciences Union
General Assembly Conference Abstracts, 14, 3464.
Troshichev, O.A., A. Frank-Kamenetsky, G. Burns, M.
Fuellekrug, A. Rodger and V. Morozov (2004). The
relationship between variations of the atmospheric
HELMAN
16
17
electric field in the southern polar region and thun-
derstorm activity, Adv. Space Res., 34, 1801-1805.
Uman, M.A., and E.P. Krider (1982). A review of natu-
ral lightning: Experimental data and modeling, IEEE
Trans. Electromagn. Compat., EMC-24, 79-112.
Uman, M.A. (1994). Natural lightning, IEEE Trans. Ind.
Appl., 30, 785e90; doi:10.1109/ICPS.1993.290594.
Uyeda, S., M. Kamogawa and H. Tanaka (2009). Analy-
sis of electrical activity and seismicity in the natural
time domain for the volcanic-seismic swarm activity
in 2000 in the Izu Island region, Japan, J. Geophys.
Res.: Solid Earth, 114, B02310; doi:10.1029/2007JB
005332.
Uyeshima, M., H. Utada and Y. Nishida, (2001). Net-
work-magnetotelluric method and its first results in
central and eastern Hokkaido, NE Japan, Geophys.
J. Int., 146, 1-19.
Varotsos, P., K. Alexopoulos and M. Lazaridou (1993).
Latest aspects of earthquake prediction in Greece
based on seismic electric signals, II, Tectonophysics,
224, 1-37.
Varotsos, P.A., N.V. Sarlis and E.S. Skordas (2011). Nat-
ural Time Analysis: The New View of Time, Berlin,
Springer-Verlag, 449 pp.
Verrier, V., and P. Rochette (2002). Estimating peak cur-
rents at ground lightning impacts using remanent
magnetization, Geophys. Res. Lett., 29, 14.1-14.4.
Viljanen, A., O. Amm and R. Pirjola (1999). Modeling
geomagnetically induced currents during different
ionospheric situations, J. Geophys. Res., 104, 28059-
28071.
Viljanen, A., A. Pulkkinen, R. Pirjola, K. Pajunpää, P.
Posio and A. Koistinen (2006). Recordings of geo-
magnetically induced currents and a nowcasting serv-
ice of the Finnish natural gas pipeline system, Space
Weather, 4, S10004; doi:10.1029/2006SW000234.
Voigt, W. (1910). Lehrbuch der kristallphysik, mit auss-
chluss der kristalloptik (Textbook on crystal physics,
excluding crystal optics), Berlin, Druck und Verlag
von B.G. Teubner, 964 pp.
von Baeckmann, W., W. Schwenk and W. Prinz (1997).
Handbook of Cathodic Corrosion Protection, Hous-
ton, Texas, Gulf Professional Publishing, 568 pp.
Walker, C.V. (1861). On magnetic storms and Earth-
currents, Phil. Trans. R. Soc. London, 151, 89-131.
Wescott, E.M., and D.D. Sentman (2002). Geophysical
electromagnetic sounding using HAARP, Depart-
ment of the Navy, Office of Naval Research (ONR)
Grant No. N00014-97-1-0995, 13 pp.
Wong, J.S.H., R.E. Hicks and R.F. Probstein (1997).
EDTA-enhanced electroremediation of metal-cont-
aminated soils, J. Hazard. Mater., 55, 61-79.
Xuhui Shen, Xuemin Zhang, Lanwei Wang, Huaran
Chen, Yun Wu, Shigeng Yuan, Junfeng Shen, Shu-
fan Zhao, Jiadong Qian and Jianhai Ding (2011). The
earthquake-related disturbances in ionosphere and
project of the first China seismo-electromagnetic
satellite, Earthquake Science, 24, 639-650.
Yamaguchi, T., and S. Hashimoto (2012). A green bat-
tery by pot-plant power, IEEJ Trans. Electr. Electr.,
7, 441-442.
Yoshino, T., G. Manthilake, T. Matsuzaki and T. Kas-
tura (2008). Dry mantle transition zone inferred
from the conductivity of wadsleyite and ringwood-
ite, Nature, 451, 326-329.
Yoshino, T. (2010). Laboratory electrical conductivity
measurement of mantle minerals, Surv. Geophys.,
31, 163-206.
Zhang Yun-qiang, Li Sheng-rong, Chen Hai-yan, Xue
Jian-ling, Sun Wen-yan and Zhang Xu (2010). Re-
search on the typomorphisms of compositions and
thermoelectric characteristics of pyrite from Zhao-
daoshan gold deposit in the eastern Shanding
province, Journal of Mineralogy and Petrology, 03,
http://en.cnki.com.cn/Article_en/CJFDTOTAL-
KWYS201003003.htm (May 2012).
Zhdanov, M.S., R.B. Smith, A. Gribenko, M. Cuma and
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,
Geophys. Res. Lett., 38, L08307; doi:10.1029/2011
GL046953.
Zlotnicki, J., and Y. Nishida (2003). Review on mor-
phological insights of self-potential anomalies on
volcanoes, Surv. Geophys., 24, 291-338.
Zolotov, O.V., A.A. Mangaladze, I.E. Zakharenkova,
O.V. Martynenko and I.I. Shagimuratov (2012).
Physical interpretation and mathematical simula-
tion of ionospheric precursors of earthquakes at
midlatitudes, Geomagnetism and Aeronomy, 52,
390-397.
*Corresponding author: Daniel S. Helman,
California State University Long Beach, Department of Geological
Sciences, Long Beach, CA, United States;
email: danielhelmanteaching@yahoo.com.
© 2013 by the Istituto Nazionale di Geofisica e Vulcanologia. All
rights reserved.
EARTH ELECTRICITY: A REVIEW OF MECHANISMS
... The following figure shows the plot of dF of Pondicherry Observatory . Baseline + e AbsH (t) + e ∆H (t) + e dF Drif t (t) (14) or in general, for the magnetic component B, ...
... The variation in gradient can happen due to many reasons depending upon the crustal structure of the locality, the soil chemistry of the observatory premises and even by the flow of ground water. Daniel Hellman [14] discusses about the current generated by the electrokinetic effect produced by the flow of groundwater. Toshiaki Mishima et al [13] has found a correlation between the annual variations in the baselines caused by changes in soil magnetization in response to temperature changes. ...
... Andras Csontos [14] have found that baseline variation of Tihany observatory shows a good correlation with the water level of the nearby lake Kulso. They have found the presence of magnetite in the water of lake Kulso and the lake Belso. ...
Conference Paper
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.
... This high resistivity stratum however, may or may not represent oil-bearing formation. Only stratum with a high amplitude resonance response and a wide range of phase angle variation [10,11] indicate a highly saturated hydrocarbon-bearing formation. The present work employs a phase-synchronized signal-detection system to acquire information in regard with the present and the abundance of oil deposits as well examining the quality of the seal rocks. ...
... A stratum with low resistivity, such as saline-water-filled sands, gives low amplitude resonance response wide range phase angle variation as well. A stratum which contains smaller amount of hydrocarbon fluids, i.e. low saturation reservoir, gives low amplitude of resonance response but still shows a significantly wide range phase angle variation resulted from ionic activities of hydrocarbon fluids [11]. Low amplitude resonance response and narrow range phase angle variation characterize a stratum of bearing no hydrocarbon fluids. ...
Article
Full-text available
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.
... The electrons and p-holes meet at the p-n junction to close the battery circuit (Fig. 2c). This model has been broadly used to account for the preseismic EM phenomena (Freund et al. 2006;Uyeda 2013;Helman 2014;Sevgi 2014), however, it can be questioned as follows: ...
Preprint
Full-text available
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.
... The shape of the Earth's magnetic field can be approximated by a magnetic dipole, but there may be notable local deviations in which the strength and the actual shape fluctuate on time scales of milliseconds and hours (Hayakawa et al. 2004) to millions of years (McElhinny and McFadden 1998). These natural atmospheric (and cosmic) electromagnetic fields are also an important driver of Earth currents (or telluric currents), and their dynamics, in both soil and water (for review see: Lanzerotti and Gregori 1986;Helman 2013). ...
Article
Full-text available
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.
... Most of the studies usually assume that these observations could be explained by a previously unrecognized (Helman, 2013) source of telluric currents in general. ...
Preprint
Full-text available
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.
... All electrical installations have grounding systems and inject electric currents into the ground, which may influence the electric potential of the ground surface. 35,36 To determine whether the results obtained in this study originated from this current, the electric potential difference between two points of a volume of sand contained in a plastic container were measured on site using the same set-up. The same potential difference of the ground was also detected in the container. ...
Article
Full-text available
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.
... The variation in gradient can happen due to many reasons depending upon the crustal structure of the locality, the soil chemistry of the observatory premises and even by the flow of ground water. Daniel Hellman [24] discusses about the current generated by the electrokinetic effect produced by the flow of groundwater. Toshiaki Mishima et al. [25] has found a correlation between the annual variations in the baselines caused by changes in soil magnetization in response to temperature changes. ...
Article
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.
... Le problème posé pour la définition de précurseurs à partir de la météorologie spatiale est plus complexe. Selon Helman [14], plusieurs types de phénomènes naturels sont à l'origine de courants telluriques, les courants électriques les plus forts étant ceux liés aux éclairs et aux conditions de la météorologie spatiale. Sous réserve de pouvoir faire la distinction entre signaux électriques sismiques et autres événements électrique l'auteur considère qu'il doit être possible de prévoir des tremblements de Terre. ...
Conference Paper
Full-text available
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.
... Various physical processes can cause stress-stimulated current (SSC) to flow when rocks are subjected to deviatoric stresses (Park et al., 1993;Johnston, 1997;Freund, 2002;Helman, 2013). These include rapid fluid pumping (electrokinetic effects), material rupture (triboelectric effects), and piezoelectric effects. ...
Article
Full-text available
Abstract We investigate charge generation as a function of stress in fine-grained gabbro for both nominally dry samples and samples fully saturated with electrically conductive brine fluids similar to those observed in active earthquake fault zones. These experiments address a number of proposed and reported electrical precursory and coseismic phenomena associated with earthquakes. Compressive load was ap-plied to one end of the sample in repetitive cycles using a pair of precision steel platens driven by a large hydraulic press. The samples were tested by cycling between con-stant low stress and constant high stress values with a 200-s periodicity. Net charge transport between the stressed and unstressed sample ends was monitored with a pi-coammeter. For the nominally dry samples, stress-stimulated current (SSC) transients on the order of 50–400 pA peak-to-peak were observed with a decay time constant ~10 seconds during stress loading and unloading. Under constant compressive loads of ~22 MPa, small negative polarity SSC of ~15 pA magnitude was observed as an offset from the baseline current at low load (5 MPa) conditions. For the fluid-saturated samples, neither transients nor stress-stimulated currents were observed as a function of stress when the load was cycled, an observation that is consistent with more rapid internal self-discharge due to higher electrical conductivity of the sample. Since the Earth’s crust is fluid saturated, observation of significant electrical charge buildup is not expected during the observed slow stress accumulation prior to earthquakes or during any slow precursory stress release that may occur in the region of earthquake nucleation. However, observation of coseismic charge generation due to electrokinetic, triboelectric, and other processes may occur during earthquake stress drops, surface rupture and seismic wave arrivals from dynamic rupture.
... And really, because of high electric conductivity of ocean water, effect of the perturbed telluric field should be strengthened. In such conditions it is admissible to transmit radio-frequency electromagnetic radiation into the ionosphere, the might take place with the electrolytes in the ocean acting as an antenna (4). ...
Article
Full-text available
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.
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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.
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Full-text available
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.
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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.
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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.
Chapter
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.
Book
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.
Conference Paper
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.