Analysis and 3D inversion of magnetotelluric crooked profile data from central Svalbard for geothermal application

Beka, Thomas Ibsa; Smirnov, Maxim; Birkelund, Yngve; Senger, Kim; Bergh, Steffen G.

doi:10.1016/j.tecto.2016.07.024

Cited by 21 publications

(21 citation statements)

References 55 publications

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“…Previously reported results from 2D (Beka et al 2015) and 3D (Beka et al 2016) MT data interpretations of the broadband range (0.003-1000 s), acquired in the socalled Central Tertiary Basin of Spitsbergen (Dallmann 1999) east of Longyearbyen (Fig. 1a), display good agreement with geological models for the region (Bergh et al 1997;Baelum & Braathen 2012;Blinova et al 2012).…”

Section: Introductionsupporting

confidence: 73%

“…Magnetotelluric surveys have been carried out in Svalbard since 2013, motivated by reconnaissance geothermal exploration, focusing particularly on areas around the permanently settled regions of central and north-western Spitsbergen (Beka et al 2015;Beka et al 2016;Beka et al 2017). This series of surveys was the first to apply the magnetotellurics method in a region whose geological structures were previously inferred mainly from surface fieldwork, seismic and gravity studies (Haremo et al 1990;Eiken 1994;Bergh et al 1997;Harland 1997;Bergh & Grogan 2003), and with scarce data to deduce the framework of the deep crustal structure.…”

Section: Introductionmentioning

confidence: 99%

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Magnetotelluric signatures of the complex tertiary fold–thrust belt and extensional fault architecture beneath Brøggerhalvøya, Svalbard

et al. 2017

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Magnetotelluric (MT) data were recently collected on Brøggerhalvøya, Svalbard, in a 0.003-1000 s period range along a curved WNW-ESE profile. The collected data manifested strong three-dimensional (3D) effects. We modelled the full impedance tensor with tipper and bathymetry included in 3D, and benchmarked the result with determinant data two-dimensional (2D) inversion. The final inversion results indicated striking similarity with known surface bedrock geology and well reflected the tectonic history of the region. The most convincing contribution of the MT data is perhaps the elegantly imaged interplay between repeated basement-involved fold-thrust belt structures and successive down-dropped strata along steeply dipping oblique-normal faults (e.g., the Scheteligfjellet Fault) that created a horst/ridge and graben/depression system. Peculiarly, the MT result suggests that the Paleocene-Eocene fold-thrust belt structures dominate the shallow crustal level, while later normal faults in the area can be traced deeper into the pre-Devonian basement formations strongly affecting fluid and heat migration towards the surface. Near the sub-vertical Scheteligfjellet Fault, the MT model indicates aquifers within the upraised horsts of the pre-Devonian system at 2-5 km depth, sandwiched between the down-faulted resistive (ca. 500-3000 Ωm) Carboniferous and Permian successions. The section west of the Ny-Ålesund settlement has signatures of lateral and subvertical cap-rock sealings, surrounding a steep and deep-seated major fault and aquifer systems. This section of the peninsula therefore requires closer investigation to evaluate the deep geothermal resource prospect.

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Section: Introductionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 99%

Magnetotelluric signatures of the complex tertiary fold–thrust belt and extensional fault architecture beneath Brøggerhalvøya, Svalbard

et al. 2017

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“…The first tests involved the bathymetry profile. Beka et al (2016) argued that shorter period data are not strongly affected by seawater, and indeed, the sea is quite shallow (<100 m) for ~70 km along the profile (Jakobsson et al, 2012). However, the sea deepens to >2 km ~170 km west of the profile as the Knipovich Ridge is approached (Figure 1a), and the inductive response of this large conductor is likely to affect the longer period data if they are sensitive to features several hundred kilometers distant.…”

Section: Inversionmentioning

confidence: 99%

Magnetotelluric Constraints on the Temperature, Composition, Partial Melt Content, and Viscosity of the Upper Mantle Beneath Svalbard

Selway

Smirnov

Beka

et al. 2020

Geochem Geophys Geosyst

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Long-period magnetotelluric (MT) data can be used to interpret upper mantle temperature, hydrogen content, and the presence of partial melt, all of which strongly influence mantle viscosity. We have collected the first long-period MT data in Svalbard and have combined them with preexisting broadband MT data to produce a model of the electrical resistivity of Svalbard's upper mantle. Asthenospheric resistivities are low compared to stable continental settings but more comparable to young oceanic asthenosphere, suggesting that the physical state of Svalbard's upper mantle is controlled by its proximity to the Mid-Atlantic Ridge. Interpretation of the MT model using a petrologically constrained genetic algorithm approach shows that partial melt is present in the uppermost asthenosphere beneath Svalbard. This is the first direct evidence of partial melt in Svalbard's asthenosphere from deep geophysical soundings. Viscosities calculated from the geophysical data show a low viscosity layer (~10 18 Pa s) coincident with the partial melt layer, underlain by a higher viscosity layer (~10 20 Pa s) extending to the transition zone. Viscosities calculated from glacial isostatic adjustment (GIA) data in Svalbard show a considerable range due mainly to uncertainties in past ice sheet models. Improved constraints on Svalbard's mantle viscosity from geophysical data may help to improve these GIA models.

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“…Electromagnetic (EM) methods, such as the magnetotelluric (MT) method, the audio magnetotelluric (AMT) method, and controlled source EM, use the EM diffusion over a wide frequency band range to detect the subsurface geo-electrical structure, from shallow near-surface to great depth [1,2]. It has been widely applied in deep tectonic study, oil and gas detection, mineral exploration, geothermal survey, engineering purposes, and environmental monitoring [3][4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Effect of Displacement Current on the Finite-Difference Modeling of Natural Source Electromagnetic Diffusion

Xue

Liu

et al. 2020

Applied Sciences

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For electromagnetic (EM) modeling based on the electric-field formulation at low frequencies, the quasi-static approximation (i.e., only the conduction current is considered and the displacement current is ignored) is commonly applied, and a small conductivity value for the air layer is chosen subjectively. Actually, in the air layer, due to the use of the small conductivity value, the quasi-static approximation is ubiquitously violated. However, the effect of the violation of the quasi-static approximation in the air on EM modeling is not well examined in the literature. In this paper, we investigate this issue by comparing the finite-difference modeling results from the calculation with the quasi-static approximation and those considering both the conduction and displacement currents. For the quasi-static approximation, the conductivity in the air is set to be different small values, and zero air conductivity is used for the modeling with both the conduction and displacement currents considered. Several simple models are designed to verify the numerical solution and study how the assigned conductivity for the air affects the modeling accuracy. One flat model and two models with topography are designed to examine the effect of the quasi-static approximation on the EM modeling results. For frequencies used in typical geophysical applications of EM diffusion, using the quasi-static approximation is able to produce accurate modeling results for models with typical earth conductivity. However, if the rough surface topography is considered, the use of the quasi-static approximation can reduce the EM modeling accuracy substantially at much lower frequencies (as low as several hundred Hz), which is probably due to the inaccurate description of EM waves in the air, and poses problems for applications based on direct EM field interpretation.

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Analysis and 3D inversion of magnetotelluric crooked profile data from central Svalbard for geothermal application

Cited by 21 publications

References 55 publications

Magnetotelluric signatures of the complex tertiary fold–thrust belt and extensional fault architecture beneath Brøggerhalvøya, Svalbard

Magnetotelluric signatures of the complex tertiary fold–thrust belt and extensional fault architecture beneath Brøggerhalvøya, Svalbard

Magnetotelluric Constraints on the Temperature, Composition, Partial Melt Content, and Viscosity of the Upper Mantle Beneath Svalbard

Effect of Displacement Current on the Finite-Difference Modeling of Natural Source Electromagnetic Diffusion

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