Studies on Electromagnetic Induction in the Earth:
Recent advances
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MantleEditorial Board (April 2018)
Editor-in-Chief
Yasuo Ogawa, Tokyo Institute of Technology, Japan

Vice Editors-in-Chief
Masato Furuya, Hokkaido University, Japan
Solid Earth Science

Nozomu Nishitani, Nagoya University, Japan
Space Science

Editors
Valerio Acocella
Ryosuke Ando
Yosuke Aoki
Kimiyuki Asano
Nanan Balan
Stephen Bannister
Paul Bedrosian
Phil Cummins
Koji Fukuma
Shin-Chan Han
Thomas Hobiger
Hauke Hussmann
Takeo Ito
Art Jolly
Tomokazu Kobayashi

Attila Komjathy
Alexey Kuvshinov
Juanjo Ledo
Huixin Liu
Takuto Maeda
Yohei Miyake
Mitsuhiro Nakagawa
Junichi Nakajima
Haruhisa Nakamichi
Yasuhito Narita
Takuya Nishimura
Takaaki Noguchi
Masahito Nose
Makiko Ohtake
Keiji Ohtsuki

Kyoko Okino
Duggirala Pallamraju
Severine Rosat
Takeshi Sakanoi
David Shelly
Hiroko Sugioka
Benoit Taisne
Sunny TamYoshiyuki Tanaka
Yanbin Wang
Yih-Min Wu
Takuji Yamada
Mare Yamamoto
Tatsuhiro Yokoyama
Kazunori Yoshizawa

Hiroo Kanamori
Jun'ichiro Kawaguchi
Takafumi Matsui
Hitoshi Mizutani

Toshitaka Tsuda
Zhongliang Wu
Kiyoshi Yomogida

Advisory Board
Benjamin Fong Chao
Bernard Chouet
Yoshimori Honkura
Toshihiko Iyemori

Journal Scope
Earth, Planets and Space (EPS) is the official journal of the Society of Geomagnetism and Earth, Planetary
and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The
Geodetic Society of Japan, and The Japanese Society for Planetary Sciences.
EPS is a peer-reviewed, open-access journal published under SpringerOpen. It is an international journal
covering scientific articles in the entire field of earth and planetary sciences, particularly geomagnetism,aeronomy, space science, seismology, volcanology, geodesy, and planetary science. EPS also welcomesarticles in new and interdisciplinary subjects, and technical reports on instrumentation and software.
The journal was launched in 1998 and has since published over 3000 articles. All of them are available forfree on SpringerLink:
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http://earth-planets-space.springeropen.com
Submit your next research article to Earth, Planets and Space via:
https://www.editorialmanager.com/epsp
Yours sincerely,
Prof. Yasuo Ogawa
Editor-in-Chief, Earth, Planets and Space
editor-in-chief@earth-planets-space.org

Earth, Planets and Space
Siripunvaraporn et al. Earth, Planets and Space (2018) 70:47
https://doi.org/10.1186/s40623-018-0806-8

PREFACEOpen AccessSpecial issue “Studies
on electromagnetic induction in the earth:recent advances”
Weerachai Siripunvaraporn1*, Paul A. Bedrosian2, Yuguo Li3, Prasanta K. Patro4, Klaus Spitzer5 and Hiroaki Toh6

Research into electromagnetic induction of the Earth’s
and planetary interiors has increased considerably within
the last decade. The 23rd Electromagnetic Induction
Workshop (EMIW) held in Chiang Mai, Thailand, inAugust 2016 was a premier event for the international
research community to exchange the latest developmentsin the field of electromagnetic induction. This special
issue is intended to promote the activity of this vibrantand growing research community and to foster futureinterdisciplinary studies within the broader earth andplanetary sciences. It is a compilation of 10 papers consisting of full research papers, letters, express letters, anda technical report on various topics ranging from terrestrial to marine, from instrumentation to inversion, and tointerpretation.

2. Engineering applications
Limitations such as highly resistive terrains, coils thatare too long to fit in a narrow tunnel space, and theabsence of a GPS signal make it difficult to use conventional surface EM receivers to measure the signal inside
tunnels. In their work “Electromagnetic receiver withcapacitive electrodes and triaxial induction coil for tunnel exploration,” Kai et al. (2017) introduced capacitiveelectrodes and triaxial induction coils that help avoid
these limitations. They successfully developed their new
design, and their tests in a mine showed that the new
equipment can be used to measure EM signals inside
tunnels with typical noise characteristics.
Monitoring of hydraulic fracturing fluids is important for geothermal exploration. This can be conductedusing many different methods. In their paper “Monitoring hydraulic stimulation using telluric sounding,” Rees
et al. (2018) found that a telluric sounding (TS) method
is relatively cheap and easy to operate for monitoring
hydraulic fracturing at depth compared to full magnetotelluric measurement. In the synthetic studies, consistentchanges of the transfer function could be observed to be
associated with the fluid movement. However, for the real
data test from the Paralana geothermal system, South
Australia, due to the high noise level, high-quality electric field data from a controlled source may be necessary.

1. Electromagnetic modeling
Most of the inversion techniques for magnetotelluric
measurement often yield smooth structures. This makes
it difficult to locate the interface boundary between resistivity contrasts. In “Regularized magnetotelluric inversion based on a minimum support gradient stabilizing
function,” Xiang et al. (2017) proposed a new MSG stabilizing function for imaging sharp interfaces for 1-D and
2-D MT inversion. By performing tests on synthetic data,
they found that the new technique yields overall good
performance in both data fitting and model recovery,
and particularly in resolving geoelectrical interfaces. Thissuggests that the new technique will be useful for practical applications.

3. Tectonic studies
As the electrical resistivity values of rocks of the crustand upper mantle are quite sensitive to the presence
aqueous fluids and partial melts, MT plays a major rolein these scenarios. In their research paper “Regional
electrical structure of the Andean subduction zone in*Correspondence: wsiripun@gmail.com
1
Mahidol University, Bangkok, Thailand
Full list of author information is available at the end of the article© The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license,
and indicate if changes were made.

1

Studies on Electromagnetic Induction in the Earth: Recent advances
Siripunvaraporn et al. Earth, Planets and Space (2018) 70:47

Page 2 of 3

amplification of the H component of the geomagnetic
field that was recorded in the central-west region of Brazil. The anomalous behavior of the geomagnetic variations is due to the presence of a 1200-km-long conductor
and was explained on the basis of classical electrodynamics as the reflection of EM waves at this interface
with a very good conductor and the damping of the EM
wave amplitude by the skin effect during its propagation through the conductive medium. The authors proposed that a detailed MT survey be carried out prior to
the establishment of the new geomagnetic observatory
to evaluate the influence of induced currents on the geomagnetic field.

central Chile (35°–36°S) using magnetotellurics,” ReyesWagner et al. (2017) used broadband MT data acquiredin the Southern Volcanic Zone of the Andes to map the
subduction zone and establish its relation with the volcanic arc at 35°–36°S latitude. Their final resistivity model
brought out the resistive nature of the forearc structure
and also a wide region of high conductivity extending
from the volcanic front to the east indicating the highly
active magmatism of the region.
The geodynamics of the Cambay Rift Zone, India, isquite complex. Danda et al. (2017) conducted a broadband and long-period MT profile with a length of 200 km
in the area and processed the result to yield a 2-D resistivity model in their work “Geoelectric structure ofnorthern Cambay rift basin from magnetotelluric data.”
They interpreted the high-conductivity zones as fluid
emplacement in the west and the presence of fluids and/or interconnected sulfides in the east. In addition, ahighly resistive body outside of the rift zone was interpreted as an igneous granitic intrusive complex.
Tracing the Indian crustal front beneath Tibet remains
a controversial issue. In their paper “Varying Indian crustal front in the southern Tibetan Plateau as revealed bymagnetotelluric data,” Xie et al. (2017) used previous MT
data to generate a 3-D geoelectrical model in southern
Tibet to cope with the Indian crustal front. They foundconductive layers beneath the mid- to lower crust, suggesting that the Indian crustal front varies irregularly
from west to east. This observation was also supported
by seismic results.
Understanding the locked fault is very importantbecause locked zones can potentially generate a large
earthquake in the future. Karaş et al. (2017) used MTdata to produce a general 3-D resistivity model in theirresearch paper “Electrical conductivity of a locked fault:
investigation of the Ganos segment of the North Anatolian Fault (NAF) using three-dimensional magnetotellurics.” The geoelectric model brought out the fault zone
conductor (FZC) corresponding to the Ganos Fault,
ophiolitic basement, and Kesan Formation. A distributed
conduit behavior of fluid flow in the vicinity of the Ganos
Fault was interpreted. The absence of any fluid pathway
at greater depths and the mechanically strong and resistive media on both sides of the fault suggest a locked
nature of the Ganos Fault.

5. Marine EM studies
In contrast to the MT data, which show no evidenceof electrical anisotropy, recent seismic data from theNoMelt experiment presented a strong anisotropy in theupper mantle. Matsuno and Evans (2017) revisited the
MT data to answer the question of whether electricalanisotropy really existed in the data in their express letter“Constraints on lithospheric mantle and crustal anisotropy in the NoMelt area from an analysis of long-period
seafloor magnetotelluric data.” Interestingly, they foundthat electrical anisotropy is possible at lower lithosphere
depths. However, this is not related to the anisotropy
found in the seismic data at upper and mid-lithosphere
depths. Seismic anisotropy at this depth is not expected
to generate measurable MT data.
To study the nature of old oceanic upper mantle, Baba
et al. (2017) analyzed many seafloor MT data in thenorthwestern Pacific in their full research paper “Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences inthermal structure not predictable from a plate coolingmodel.” Significant differences in resistive layer thickness
were observed between the four zones of investigation,and these could not be explained by only a plate cooling model. The authors suggested that these differences
may have been caused by the influence of the plumeassociated with the formation of the Shatsky Rise or by
spatially non-uniform and small-scale convection in theasthenosphere.
Authors’ contributions
All authors of this article served as guest editors for this special issue. All
authors read and approved the final manuscript.

4. Geomagnetic studies

Author details
1
Mahidol University, Bangkok, Thailand. 2 U.S. Geological Survey, Denver, CO,USA. 3 Ocean University of China, Qingdao, China. 4 National GeophysicalResearch Institute, Hyderabad, India. 5 TU Bergakademie Freiberg, Freiberg,
Germany. 6 Kyoto University, Kyoto, Japan.

Prior to the establishment of a new geomagnetic observatory, Padilha et al. (2017) presented a research letter
titled “Effect of a huge crustal conductive anomaly on
the H component of geomagnetic variations recorded incentral South America.” The authors reported anomalous

2

Earth, Planets and Space
Siripunvaraporn et al. Earth, Planets and Space (2018) 70:47

Page 3 of 3

Acknowledgements
We express sincere appreciation to the authors who contributed to thisspecial issue and the reviewers who evaluated the contributions and provided
helpful comments and suggestions.

Karaş M, Tank SB, Özaydın S (2017) Electrical conductivity of a locked fault:
investigation of the Ganos segment of the North Anatolian Fault using
three-dimensional magnetotellurics. Earth Planets Space. https://doi.
org/10.1186/s40623-017-0695-2
Matsuno T, Evans RL (2017) Constraints on lithospheric mantle and crustal anisotropy in the NoMelt area from an analysis of long-period seafloor magnetotelluric data. Earth Planets Space 69:138. https://doi.org/10.1186/
s40623-017-0724-1
Padilha AL, Alves LR, Silva GBD, Espinosa KV (2017) Effect of a huge crustal
conductivity anomaly on the H-component of geomagnetic variations
recorded in central South America. Earth Planets Space. https://doi.
org/10.1186/s40623-017-0644-0
Rees N, Heinson G, Conway D (2018) Monitoring hydraulic stimulation using
telluric sounding. Earth Planets Space 70:7. https://doi.org/10.1186/
s40623-017-0767-3
Reyes-Wagner V, Díaz D, Cordell D, Unsworth M (2017) Regional electricalstructure of the Andean subduction zone in central Chile (35°–36°S)
using magnetotellurics. Earth Planets Space 69:142. https://doi.
org/10.1186/s40623-017-0726-z
Xiang Y, Yu P, Zhang L, Feng S, Utada H (2017) Regularized magnetotelluric
inversion based on a minimum support gradient stabilizing functional.
Earth Planets Space. https://doi.org/10.1186/s40623-017-0743-y
Xie C, Jin S, Wei W, Ye G, Zhang L, Dong H, Yin Y (2017) Varying Indian crustal
front in the southern Tibetan Plateau as revealed by magnetotelluric data.
Earth Planets Space. https://doi.org/10.1186/s40623-017-0734-z

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Received: 16 February 2018 Accepted: 16 February 2018

References
Baba K, Tada N, Matsuno T, Liang P, Li R, Zhang L, Shimizu H, Abe N, Hirano N,
Ichiki M, Utada H (2017) Electrical conductivity of old oceanic mantle in
the northwestern Pacific I: 1-D profiles suggesting differences in thermal
structure not predictable from a plate cooling model. Earth Planets
Space. https://doi.org/10.1186/s40623-017-0697-0
Danda N, Rao CK, Kumar A (2017) Geoelectric structure of northern Cambay
rift basin from magnetotelluric data. Earth Planets Space. https://doi.
org/10.1186/s40623-017-0725-0
Kai C, Sheng J, Wang S (2017) Electromagnetic receiver with capacitive electrodes and triaxial induction coil for tunnel exploration 1. Geomagnetism.
Earth Planets Space. https://doi.org/10.1186/s40623-017-0706-3

3

Studies on Electromagnetic Induction in the Earth: Recent advances

FULL PAPER

Open AccessElectrical conductivity of a locked fault: investigation of the Ganos
segment of the North Anatolian Fault using threedimensional magnetotellurics
Mustafa Karaş, Sabri Bülent Tank* and Sinan Özaydın
Earth, Planets and Space 2017, 69:107 DOI:10.1186/s40623-017-0695-2
Received: 3 January 2017, Accepted: 31 July 2017, Published: 15 August 2017

Abstract
This study attempts to reveal the fault zone characteristics of the locked Ganos Fault based on electrical resistivity studies
including audio-frequency (AMT: 10,400–1 Hz) and wide-band (MT: 360–0.000538 Hz) magnetotellurics near the epicenter ofthe last major event, that is, the 1912 Mürefte Earthquake (Mw 7.4). The AMT data were collected at twelve stations, closely
spaced from north to south, to resolve the shallow resistivity structure to 1 km depth. Subsequently, 13 wide-band MT
stations were arranged to form a grid enclosing the AMT profile to decipher the
deeper structure. Three-dimensional inverse modeling indicates highly conductive
anomalies representing fault zone conductors along the Ganos Fault. Subsidiaryfaults around the Ganos Fault, which are conductive structures with individual
mechanically weak features, merge into a greater damage zone, creating a wide
fluid-bearing environment. This damage zone is located on the southern side of thefault and defines an asymmetry around the main fault strand, which demonstrates
distributed conduit behavior of fluid flow. Ophiolitic basement occurs as lowconductivity block beneath younger formations at a depth of 2 km, where themechanically weak to strong transition occurs. Resistive structures on both sides ofthe fault beneath this transition suggest that the lack of seismicity might be related tothe absence of fluid pathways in the seismogenic zone.

Keywords: Fluid, North Anatolian Fault, Ganos Fault, Fault zone conductor, Locked
fault, Electrical resistivity, Asymmetric damage zone, Magnetotellurics

Graphical abstract*Corresponding author: Sabri Bülent Tank, bulent.tank@boun.edu.tr

FULL PAPER

Open AccessElectrical conductivity of old oceanic mantle in the northwestern
Pacific I: 1-D profiles suggesting differences in thermal structure notpredictable from a plate cooling model
Kiyoshi Baba*, Noriko Tada, Tetsuo Matsuno, Pengfei Liang, Ruibai Li, Luolei Zhang,
Hisayoshi Shimizu, Natsue Abe, Naoto Hirano, Masahiro Ichiki and Hisashi Utada
Earth, Planets and Space 2017, 69:111 DOI:10.1186/s40623-017-0697-0
Received: 30 April 2017, Accepted: 31 July 2017, Published: 15 August 2017

Abstract

nin
Tre
n

ch

Seafloor magnetotelluric (MT) experiments were recently conducted in two areas of the northwestern Pacific to investigate the nature of theold oceanic upper mantle. The areas are far from any tectonic activity, and “normal” mantle structure is therefore expected. The data were
carefully analyzed to reduce the effects of coastlines and seafloor topographic changes, which are significant boundaries in electricalconductivity and thus distort seafloor MT data. An isotropic, one-dimensional electricalconductivity profile was estimated for each area. The profiles were compared with those
h
renc
an T
obtained from two previous study areas in the northwestern Pacific. Between the fourJap
profiles, significant differences were observed in the thickness of the resistive layer
Rise
tsky
beyond expectations based on cooling of homogeneous oceanic lithosphere over time.
Sha
This surprising feature is now further clarified from what was suggested in a previous
study. To explain the observed spatial variation, dynamic processes must be introduced,
such as influence of the plume associated with the formation of the Shatsky Rise, or
−0.5
−1.0
spatially non-uniform, small-scale convection in the asthenosphere. There is significant−1.5
room of further investigation to determine a reasonable and comprehensive
−2.0
−2.5
interpretation of the lithosphere–asthenosphere system beneath the northwestern−3.0
Pacific. The present results demonstrate that electrical conductivity provides key−3.5
information for such investigation.
Petit−

Are(130 a A
Ma)Are(140 a B
Ma)

Depth [km]250 200 150 100 50

0Are(135 a D
Ma)Are(147 a C
Ma)

Keywords: Geomagnetic induction, Marine magnetotellurics, Electrical conductivity,
Oceanic lithosphere and asthenosphere, Northwestern Pacific*Corresponding author: Kiyoshi Baba, kbaba@eri.u-tokyo.ac.jp
4Graphical abstractlog conductivity [S m−1]

Bo

spot

Earth, Planets and Space

FULL PAPER

Open AccessGeoelectric structure of northern Cambay rift basin frommagnetotelluric data
Nagarjuna Danda, C. K. Rao* and Amit Kumar
Earth, Planets and Space 2017, 69:140 DOI:10.1186/s40623-017-0725-0
Received: 4 May 2017, Accepted: 27 September 2017, Published: 6 October 2017

Abstract
Broadband and long-period magnetotelluric data were acquired over the northern part of the Cambay rift zone along aneast–west profile ~ 200 km in length. The decomposed TE- and TM-mode data were inverted using a 2-D nonlinear conjugate
gradient algorithm to obtain the lithospheric structure of the region. A highly conductive (~ 1000 S) layer was identified
within the Cambay rift zone and interpreted as thick Quaternary and Tertiary sediments. The crustal conductors found in the
profile were due to fluid emplacement in the western part, and the presence of fluids and/or interconnected sulfides causedby metamorphic phases in the eastern part. The demarcation of the Cambay
rift zone is clearly delineated with a steeply dipping fault on the western
margin, whereas the eastern margin of the rift zone gently dips along the
NE–SW axis, representing a half-graben structure. A highly resistive body
identified outside the rift zone is interpreted as an igneous granitic intrusivecomplex. Moderately conductive (30–100 Ω-m) zones indicate underplating
and the presence of partial melt due to plume–lithosphere interactions.

Keywords: Cambay rift zone, Deccan basalt, Lithosphere, Magnetotellurics,
Reunion plume

Graphical abstract*Corresponding author: C. K. Rao, ckrao@iigs.iigm.res.in; ckraochinta@gmail.com

FULL PAPER

Open AccessRegional electrical structure of the Andean subduction
zone in central Chile (35°–36°S) using magnetotellurics
Valentina Reyes-Wagner*, Daniel Díaz, Darcy Cordell and Martyn Unsworth
Earth, Planets and Space 2017, 69:142 DOI:10.1186/s40623-017-0726-z
Received: 24 April 2017, Accepted: 29 September 2017, ublished: 12 October 2017

Abstract
A profile of broadband magnetotelluric stations was acquired between 2009 and 2016 at 35°–36°S in the Southern Volcanic
Zone of the Chilean Andes to image the subduction zone and its relation with the volcanic arc at this latitude. This transect
extends from the Coastal Cordillera across the Central Valley and the volcanic arc of the Principal Cordillera to the Argentine
border. Two active volcanic complexes are found along this profile: Tatara-San Pedro is located on the modern volcanic front,
and the Laguna del Maule volcanic field is found approximately 30 km to the east. The latter exhibits considerable signs ofunrest, such as uplift rates of up to 25 cm/year, and has produced a high concentration of silicic eruptions in the last 25 ky. The
data covered the period range from 0.001 to 1000 s. Robust processing techniques were used, including remote reference,and dimensionality was investigated by estimation of geoelectric strike, skew and analysis of the induction arrows. The data
were modeled using a 2D inversion algorithm to produce a resistivity model which was consistent with surface geology andseismicity. The final resistivity model shows a generally resistive
fore-arc structure, coincident with the tectonic environment,
and a wide conductive region from the volcanic front to theeast. This suggests a broad region of magmatism throughout
the arc, related to three distinct magma bodies, associated with
the Tatara-San Pedro and Laguna del Maule volcanic complexes
and the Mariposa Geothermal System.

Keywords: Magnetotellurics, Volcanism, Southern Volcanic
Zone, Deformation, Subduction zone

Graphical abstract*Corresponding author: Valentina Reyes-Wagner, valentina.reyes@ug.uchile.cl5

Studies on Electromagnetic Induction in the Earth: Recent advances

FULL PAPER

Open Access

Varying Indian crustal front in the southern Tibetan Plateau
as revealed by magnetotelluric data
Chengliang Xie*, Sheng Jin, Wenbo Wei, Gaofeng Ye, Letian Zhang, Hao Dong and Yaotian Yin
Earth, Planets and Space 2017, 69:147 DOI:10.1186/s40623-017-0734-z
Received: 2 May 2017, Accepted: 17 October 2017, Published: 25 October 2017

Abstract

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In the southern Tibetan plateau, which is considered to be the ongoing India–Eurasia continental collision zone, tracing of the Indiancrustal front beneath Tibet is still controversial. We conducted deep subsurface electrical modeling in southern Tibet and discuss thegeometry of the front of the Indian crust. Three areas along the Yarlung-Zangbo river zone for which previous magnetotelluric (MT)data are available were inverted independently using a three-dimensional MT inversion algorithm ModEM. Electrical horizontal slices atdifferent depths and north–south oriented cross sections at different longitudes were obtained to provide a geoelectrical perspective
for deep processes beneath the Tethyan Himalaya and Lhasa terrane. Horizontal slices at depths greater than − 15 km show that theupper crust is covered with resistive layers. Below a depth of − 20 km, discontinuous conductive distributions are primarily
concentrated north of the Yarlung-Zangbo sutures (YZS) and could be imaged frommid- to lower crust. The results show that the maximum depth to which theresistive layers extend is over − 20 km, while the mid- to lower crustal conductive
zones extend to depths greater than − 50 km. The results indicate that the
conductive region in the mid- to lower crust can be imaged primarily from the YZS
to south of the Bangong-Nujiang sutures in western Tibet and to ~ 31°N in eastern
Tibet. The northern front of the conductive zones appears as an irregular barrier tothe Indian crust from west to east. We suggest that a relatively less conductive
subsurface in the northern portion of the barrier indicates a relatively cold andstrong crust and that the front of the Indian crust might be halted in the south of thebarrier. We suggest that the Indian crustal front varies from west to east and has atleast reached: ~ 33.5°N at ~ 80°E, ~ 31°N at ~ 85°E, and ~ 30.5°N at ~ 87°E and ~ 92°E.
˚

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MantleMantleKeywords: Indian crust, Southern Tibet, Electrical model, Partial melt

Graphical abstract*Corresponding author: Chengliang Xie, clx@cugb.edu.cn

FULL PAPER

Open AccessRegularized magnetotelluric inversion based on aminimum support gradient stabilizing functional
Yang Xiang, Peng Yu*, Luolei Zhang, Shaokong Feng and Hisashi Utada
Earth, Planets and Space 2017, 69:158 DOI:10.1186/s40623-017-0743-y
Received: 2 March 2017, Accepted: 7 November 2017, Published: 21 November 2017

Abstract
Regularization is used to solve the ill-posed problem of magnetotelluric inversion usually by adding a stabilizing functional to theobjective functional that allows us to obtain a stable solution. Among a number of possible stabilizing functionals, smoothing
constraints are most commonly used, which produce spatially smooth inversion results. However, in some cases, the focused imaging
of a sharp electrical boundary is necessary. Although past works have proposed functionals that may be suitable for the imaging of a
sharp boundary, such as minimum support and minimum gradient support (MGS)
functionals, they involve some difficulties and limitations in practice. In this paper, we
propose a minimum support gradient (MSG) stabilizing functional as anotherpossible choice of focusing stabilizer. In this approach, we calculate the gradient of
the model stabilizing functional of the minimum support, which affects both thestability and the sharp boundary focus of the inversion. We then apply the discrete
weighted matrix form of each stabilizing functional to build a unified form of theobjective functional, allowing us to perform a regularized inversion with variety ofstabilizing functionals in the same framework. By comparing the one-dimensional
and two-dimensional synthetic inversion results obtained using the MSG stabilizing
functional and those obtained using other stabilizing functionals, we demonstratethat the MSG results are not only capable of clearly imaging a sharp geoelectricalinterface but also quite stable and robust. Overall good performance in terms of bothdata fitting and model recovery suggests that this stabilizing functional is effective
and useful in practical applications.

Keywords: Regularized inversion, Stabilizing functional, Minimum support gradient*Corresponding author: Peng Yu, yupeng@tongji.edu.cn
6Graphical abstract

Earth, Planets and Space

FULL PAPER

Open Access

Monitoring hydraulic stimulation using telluric sounding
Nigel Rees*, Graham Heinson and Dennis Conway
Earth, Planets and Space 2018, 70:7 DOI:10.1186/s40623-017-0767-3
Received: 27 April 2017, Accepted: 19 December 2017, Published: 11 January 2018

Abstract
The telluric sounding (TS) method is introduced as a potential tool for monitoring hydraulic fracturing at depth. The
advantage of this technique is that it requires only the measurement of electric fields, which are cheap and easy whencompared with magnetotelluric measurements. Additionally, the transfer function between electric fields from two locations
is essentially the identity matrix for a 1D Earth no matter what the vertical structure. Therefore, changes in the earth resulting
from the introduction of conductive bodies underneath one of these sites can be associated with deviations away from theidentity matrix, with static shift appearing as a galvanic multiplier at all periods. Singular value decomposition and eigenvalue
analysis can reduce the complexity of the resulting telluric distortion matrix to simpler parameters that can be visualised in
the form of Mohr circles. This technique would be useful in constraining the lateral extent of resistivity changes. We test theviability of utilising the TS method for monitoring on both a synthetic dataset and fora hydraulic stimulation of an enhanced geothermal system case study conducted in
Paralana, South Australia. The synthetic data example shows small but consistentchanges in the transfer functions associated with hydraulic stimulation, with grids ofMohr circles introduced as a useful diagnostic tool for visualising the extent of fluid
movement. The Paralana electric field data were relatively noisy and affected by thedead band making the analysis of transfer functions difficult. However, changes in theorder of 5% were observed from 5 s to longer periods. We conclude that deep
monitoring using the TS method is marginal at depths in the order of 4 km and that inorder to have meaningful interpretations, electric field data need to be of a highquality with low levels of site noise.

Keywords: Telluric sounding, Hydraulic stimulation, Monitoring, Transfer functions

Graphical abstract*Corresponding author: Nigel Rees, nigel.rees@anu.edu.au

LETTER

Open Access

Effect of a huge crustal conductivity anomaly on the H-componentof geomagnetic variations recorded in central SouthAmericaAntonio L. Padilha*, Livia R. Alves, Graziela B. D. Silva and Karen V. Espinosa
Earth, Planets and Space 2017, 69:58 DOI:10.1186/s40623-017-0644-0
Received: 9 December 2016, Accepted: 14 April 2017, Published: 26 April 2017

Abstract
We describe here an analysis of the H-component of the geomagnetic field recorded in several temporary stations operating
simultaneously in the central–eastern region of Brazil during nighttime pulsation events in 1994 and the sudden commencement of
the St. Patrick’s Day magnetic storm in 2015. A significant amplification in the amplitude of the geomagnetic variations is consistently
observed in one of these stations. Magnetovariational analysis indicates that theamplification factor is period dependent with maximum amplitude around 100 s.
Integrated magnetotelluric (MT) and geomagnetic depth soundings (GDS) have shownthat this station is positioned just over a huge 1200-km-long crustal conductor(estimated bulk conductivity greater than 1 S/m). We propose that the anomalous
signature of the geomagnetic field at this station is due to the high reflection coefficientof the incident electromagnetic wave at the interface with the very good conductor andby skin effects damping the electromagnetic wave in the conducting layers overlying the
conductor. There are some indication from the GDS data that the conductor extends
southward beneath the sediments of the Pantanal Basin. In this region is being planned
the installation of a new geomagnetic observatory, but its preliminary data suggest
anomalous geomagnetic variations. We understand that a detailed MT survey must be
carried out around the chosen observatory site to evaluate the possible influence of
induced currents on the local geomagnetic field.
−12˚

GDS

−14˚

MT

CB

predicted

0.5
0.5

7

11

7

observed

10

−16˚

km

PN

0

−56˚

−54˚

−52˚

100

−50˚

10

11

7

CB

7

−58˚

Ωm

Depth (km)

0

3

20

2

30

1
0

40

Keywords: South America, Geomagnetic variations, Crustal conductor, Geomagnetic
observatory, Reflection of electromagnetic waves, Skin effect*Corresponding author: Antonio L. Padilha, antonio.padilha@inpe.br
7

4

10

50

NW

200

250

300

350

Distance (km)Fig. 5

400

450

−1
Log[ ρ ]SE

Studies on Electromagnetic Induction in the Earth: Recent advances

EXPRESS LETTER

Open Access

Constraints on lithospheric mantle and crustal anisotropy in the
NoMelt area from an analysis of long-period seafloor
magnetotelluric data
Tetsuo Matsuno* and Rob. L. Evans
Earth, Planets and Space 2017, 69:138 DOI:10.1186/s40623-017-0724-1
Received: 28 April 2017, Accepted: 25 September 2017, Published: 5 October 2017

Abstract

Depth [km]Despite strong anisotropy seen in analysis of seismic data from the NoMelt experiment in 70 Ma Pacific seafloor, a previous
analysis of coincident magnetotelluric (MT) data showed no evidence for anisotropy in the electrical conductivity structure ofeither lithosphere or asthenosphere. We revisit the MT data and use 1D anisotropic models of the lithosphere to demonstrate
the limits of acceptable anisotropy within the data. We construct 1D models by varying the thickness and the degree ofanisotropy within the lithosphere and conduct a series of tests to
Type 1
Type 2Type 3
investigate what types of electrical anisotropy are compatible with the0data. We find that electrical anisotropy is possible in a sheared and/orhydrous mantle within the lower lithosphere (60–90 km depth). Thehα50data are not compatible with pervasive electrical anisotropy in thecrust. Causes of anisotropy within the highly resistive upper and mid100
lithosphere, as seen seismically, are not expected to cause measurable
impacts on MT response.

Keywords: Electrical anisotropy, Oceanic lithosphere, Shearing, Water,

150

Central Pacific

200

6

5

4

3

2

1

log10 Resistivity [Ω−m]

0

6

5

4

3

2

1

0

6

log10 Resistivity [Ω−m]

5

4

3

2

1

0

log10 Resistivity [Ω−m]-Fig. 1*Corresponding author: Tetsuo Matsuno, matsuno@port.kobe-u.ac.jp

TECHNICAL REPORT

Open AccessElectromagnetic receiver with capacitive electrodes andtriaxial induction coil for tunnel exploration
Chen Kai, Jin Sheng* and Shun Wang
Earth, Planets and Space 2017, 69:123 DOI:10.1186/s40623-017-0706-3
Received: 8 February 2017, Accepted: 21 August 2017, Published: 11 September 2017

Abstract
A new type of electromagnetic (EM) receiver has been developed by integrating four capacitive electrodes and a triaxial induction
coil with an advanced data logger for tunnel exploration. The new EM receiver can conduct EM observations in tunnels, which is oneof the principal goals of surface-tunnel-borehole EM detection for deep ore deposit mapping. The use of capacitive electrodes
enables us to record the electrical field (E-field) signals from hard rock surfaces, which are high-resistance terrains. A compact triaxial
induction coil integrates three independent induction coils for narrow-tunnel exploration applications. A low-time-drift-error clock
source is developed for tunnel applications where GPS signals are unavailable. The three main components of our tunnel EM receiver
are: (1) four capacitive electrodes for measuring the E-field signal without digging in
hard rock regions; (2) a triaxial induction coil sensor for audio-frequency
magnetotelluric and controlled-source audio-frequency magnetotelluric signal
measurements; and (3) a data logger that allows us to record five-component MT
signals with low noise levels, low time-drift-error for the clock source, and highdynamic range. The proposed tunnel EM receiver was successfully deployed in amine that exhibited with typical noise characteristics.

Keywords: Tunnel EM prospecting, Capacitive electrode, Triaxial induction coil,
Low time-drift-error clock source, EM data logger

Graphical abstract*Corresponding author: Jin Sheng, jinsheng@cugb.edu.cn
8

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Contents
Special issue “Studies on electromagnetic induction in the earth: recent advances”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . Weerachai Siripunvaraporn, Paul A. Bedrosian, Yuguo Li, Prasanta K. Patro, Klaus Spitzer and Hiroaki Toh
Electrical conductivity of a locked fault: investigation of the Ganos segment of the North Anatolian Fault using
three-dimensional magnetotellurics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mustafa Karaş, Sabri Bülent Tank and Sinan Özaydın
Electrical conductivity of old oceanic mantle in the northwestern Pacific I: 1-D profiles suggesting differences inthermal structure not predictable from a plate cooling model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kiyoshi Baba, Noriko Tada, Tetsuo Matsuno, Pengfei Liang, Ruibai Li, Luolei Zhang, Hisayoshi Shimizu,
Natsue Abe, Naoto Hirano, Masahiro Ichiki and Hisashi Utada

Geoelectric structure of northern Cambay rift basin from magnetotelluric data
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nagarjuna Danda, C. K. Rao and Amit Kumar
Regional electrical structure of the Andean subduction zone in central Chile (35°–36°S) using magnetotellurics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Valentina Reyes-Wagner, Daniel Díaz, Darcy Cordell and Martyn Unsworth
Varying Indian crustal front in the southern Tibetan Plateau as revealed by magnetotelluric data
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chengliang Xie, Sheng Jin, Wenbo Wei, Gaofeng Ye, Letian Zhang, Hao Dong and Yaotian Yin
Regularized magnetotelluric inversion based on a minimum support gradient stabilizing functional. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yang Xiang, Peng Yu, Luolei Zhang, Shaokong Feng and Hisashi Utada
Monitoring hydraulic stimulation using telluric sounding. . . . . . . . . . . . . . . . . . . . . . Nigel Rees, Graham Heinson and Dennis Conway
Effect of a huge crustal conductivity anomaly on the H-component of geomagnetic variations recorded in central
South America. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Antonio L. Padilha, Livia R. Alves, Graziela B. D. Silva and Karen V. Espinosa
Constraints on lithospheric mantle and crustal anisotropy in the NoMelt area from an analysis of long-period seafloor
magnetotelluric data. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tetsuo Matsuno and Rob. L. Evans
Electromagnetic receiver with capacitive electrodes and triaxial induction coil for tunnel exploration. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chen Kai, Jin Sheng and Shun Wang

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Cover image: Xie, C. et al., Earth, Planets and Space 2017, 69:147 DOI:10.1186/s40623-017-0734-z