Abstract The polar regions are host to fundamental unresolved challenges in Earth studies. The nature of these regions necessitates the use of geophysics to address these issues, with electromagnetic and, in particular, magnetotelluric studies finding favour and being applied over a number of different scales. The unique geography and climatic conditions of the polar regions means collecting magnetotelluric data at high latitudes, which presents challenges not typically encountered and may result in significant measurement errors. (1) The very high contact resistance between electrodes and the surficial snow and ice cover (commonly MΩ) can interfere with the electric field measurement. This is overcome by using custom-designed amplifiers placed at the active electrodes to buffer their high impedance contacts. (2) The proximity to the geomagnetic poles requires verification of the fundamental assumption in magnetotellurics that the magnetic source field is a vertically propagating, horizontally polarised plane wave. Behaviour of the polar electro-jet must be assessed to identify increased activity (high energy periods) that create strong current systems and may generate non-planar contributions. (3) The generation of ‘blizstatic’, localised random electric fields caused by the spin drift of moving charged snow and ice particles that produce significant noise in the electric fields during periods of strong winds. At wind speeds above ~ 10 m s −1 , the effect of the distortion created by the moving snow is broad-band. Station occupation times need to be of sufficient length to ensure data are collected when wind speed is low. (4) Working on glaciated terrain introduces additional safety challenges, e.g., weather, crevasse hazards, etc. Inclusion of a mountaineer in the team, both during the site location planning and onsite operations, allows these hazards to be properly managed. Examples spanning studies covering development and application of novel electromagnetic approaches for the polar regions as well as results from studies addressing a variety of differing geologic questions are presented. Electromagnetic studies focusing on near-surface hydrologic systems, glacial and ice sheet dynamics, as well as large-scale volcanic and tectonic problems are discussed providing an overview of the use of electromagnetic methods to investigate fundamental questions in solid earth studies that have both been completed and are currently ongoing in polar regions.

Magnetotellurics

Electromagnetics

10.1007/s10712-019-09570-8

Cite

Citations (25)

Geophysical transects in the Abitibi greenstone belt of Canada from the mineral-exploration-oriented Metal Earth project

The Leading Edge (2023)

Richard S. Smith Mostafa Naghizadeh Saeid Cheraghi Ademola Q. Adetunji Rajesh Vayavur

The Metal Earth project integrates geophysics, geology, geochemistry, and geochronology to improve the understanding of metal endowment in Precambrian terranes. Magnetics (airborne), gravity, magnetotellurics, and reflection seismic methods are the primary geophysical tools employed. Data were collected along 13 transects in the initial phase of the project. All geophysical tools are crucial for understanding the structure of the shallow, middle, and deeper crust and identifying pathways along which the constituents of critical minerals might have migrated from a source to a deposit. The magnetic data are used predominantly to help map the geology away from the transects, and the gravity data are useful for extending the near-surface geology to depths up to 8 km. The magnetotelluric data show the upper Archean crust to about 10 km as highly resistive, except for some conductive subvertical zones that correspond to major deformation zones, many of which are known to be metalliferous. This suggests that these conductive zones could have been hydrothermal fluid pathways feeding the mineral deposits. These zones can be traced to larger horizontal conductive zones in the midcrust. The seismic reflection data are consistent with and complement this: the upper crust is primarily nonreflective; however, the midcrust shows many horizontal reflectors, usually with a consistent dip to the north. Processing crooked-line seismic data is problematic, and techniques have been developed to improve the imaging, including multifocusing, 3D processing, full-waveform inversion, and cross-dip moveout methods. Passive seismic data have also been collected. Ambient-noise surface-wave tomography can be used to infer broad zones of similar seismic velocity between major reflectors, while receiver function analysis has been used to identify deeper structures such as horizontal features at or below the Moho and a dipping structure evident to about 70 km depth.

Magnetotellurics

Passive seismic

10.1190/tle42040245.1

Cite

Citations (1)

Magnetotelluric imaging beneath the Taiwan orogen: An arc‐continent collision

Journal of Geophysical Research Atmospheres (2011)

E. A. Bertrand Martyn Unsworth Chih‐Wen Chiang Chow‐Son Chen Chien‐Chih Chen

The Taiwan orogen has formed since the late Miocene by oblique collision between the Luzon Volcanic Arc on the Philippine Sea Plate, and the Eurasian continental margin. This oblique collision has produced an orogen that decreases in age from north to south, and permits study of the temporal evolution of an arc‐continent collision. These factors make Taiwan a favorable location to study the process of arc‐continent collision. The first long‐period magnetotelluric (MT) measurements were recorded in Taiwan as part of the Taiwan Integrated Geodynamics Research (TAIGER) project in 2006–7. Measurements were made at 82 sites on three transects across south, central and north Taiwan, that span the breadth of the orogen and cross all major tectonic boundaries. Robust, remote reference processing of the MT time series data resulted in high‐quality soundings that were modeled in both 2 and 3‐dimensions. These MT models support predictions of lithospheric deformation (i.e., thick‐skinned tectonics) beneath the Central Ranges in south and central Taiwan, but are inconsistent with predictions of orogen‐scale thin‐skinned models. The MT resistivity model for northern Taiwan is consistent with dewatering of the subducting Philippine slab, and with deformation described by the subducting‐indenter tectonic model. Modeling the TAIGER MT data has definitively shown that conductive, and seismically active crustal structures, exist to 30+ km beneath the orogen. These conductive regions, interpreted as interconnected fluid, map pervasive zones of collisional deformation that are lithospheric in scale.

Magnetotellurics

Collision zone

geodynamics

continental collision

Island arc

10.1029/2011jb008688

Cite

Citations (53)

Magnetotelluric imaging of the Ohaaki geothermal system, New Zealand: Implications for locating basement permeability

Journal of Volcanology and Geothermal Research (2013)

E. A. Bertrand T. G. Caldwell G. J. Hill Stewart L. Bennie S. Soengkono

Magnetotellurics