Efficient 3-D controlled-source electromagnetic modelling using an exponential finite-difference method

Jaysaval, Piyoosh; Shantsev, D. V.; Ryhove, Sébastien de la Kethulle de

doi:10.1093/gji/ggv377

Cited by 13 publications

(5 citation statements)

References 33 publications

(39 reference statements)

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“…"#$ with the angular frequency " and 185 i = √−1, a quasi-static vector Helmholtz equation for the electric field can be derived from Maxwell's equations. Following Jaysaval et al (2014Jaysaval et al ( , 2015Jaysaval et al ( , 2016, we have…”

Section: Aem Data Modeling and Inversionmentioning

confidence: 99%

“…This equation is solved to compute the electric field followed by using Faraday's law to compute the magnetic field. Accuracy of the developed forward modeling software was 200 benchmarked against analytical/semi-analytical solutions for layered earth and Jaysaval et al (2014Jaysaval et al ( , 2015Jaysaval et al ( , 2016 for 3D earth models. The results agreed well, within acceptable error ranges, depending on fine-or coarse-meshing of benchmarking models.…”

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confidence: 99%

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Stratigraphic Identification with Airborne Electromagnetic Methods at the Hanford Site, Washington

Jaysaval

Robinson

Johnson

2020

Preprint

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Abstract. Stratigraphic units can influence the fate and transport of subsurface contaminants within groundwater. Units having coarse-grained sediments act as preferential flow pathways, and therefore can accelerate the transport of contaminants to reach human and ecological receptors. At legacy waste sites, detailed knowledge of subsurface stratigraphy can be used for effective monitoring and remediation planning to help minimize risk to human health and the environment. Airborne electromagnetic (AEM) methods can non-invasively provide information on kilometer-scale or larger subsurface stratigraphic features and fill informational gaps in directly sampled data from sparsely located boreholes. In this paper, we present inversion results of a 412 line-km frequency-domain AEM survey to delineate subsurface stratigraphic features at the Hanford Site, located in southeastern Washington State. The inversion was performed using a massively parallel 3D electromagnetic modeling and inversion code, where the modeling is based on solving frequency-domain Maxwell’s equations using an unstructured-mesh finite-element method and the inversion employs a Gauss-Newton optimization scheme. The results are compared to an underlying geologic framework model (GFM), built by interpolating contact depths of stratigraphic units interpreted from site borehole datasets. In areas with good borehole coverage, the inversion results show a good match with the GFM to a depth of about 60 m. Outside of these areas, the inversion results exhibit inconsistencies from the assumptions made to create the GFM, demonstrating that the AEM survey results can be used to improve the understanding of the geological conceptual model.

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Section: Aem Data Modeling and Inversionmentioning

confidence: 99%

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confidence: 99%

Stratigraphic Identification with Airborne Electromagnetic Methods at the Hanford Site, Washington

Jaysaval

Robinson

Johnson

2020

Preprint

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“…On the other hand, if the water depth is increased to 3 km, the airwave contribution becomes negligible because EM fields are strongly attenuated in the conductive sea water (see e.g. Jaysaval et al 2015). Keeping this in mind, we built a deep-water model (D-model) from the shallow-water H-model by simply removing the air layer and adding 2.9 km of seawater so that the water layer becomes 3 km thick.…”

Section: Deep Water Versus Shallow Watermentioning

confidence: 99%

Large-scale 3-D EM modelling with a Block Low-Rank multifrontal direct solver

Shantsev

Jaysaval

Ryhove³

et al. 2017

Geophysical Journal International

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S U M M A R YWe put forward the idea of using a Block Low-Rank (BLR) multifrontal direct solver to efficiently solve the linear systems of equations arising from a finite-difference discretization of the frequency-domain Maxwell equations for 3-D electromagnetic (EM) problems. The solver uses a low-rank representation for the off-diagonal blocks of the intermediate dense matrices arising in the multifrontal method to reduce the computational load. A numerical threshold, the so-called BLR threshold, controlling the accuracy of low-rank representations was optimized by balancing errors in the computed EM fields against savings in floating point operations (flops). Simulations were carried out over large-scale 3-D resistivity models representing typical scenarios for marine controlled-source EM surveys, and in particular the SEG SEAM model which contains an irregular salt body. The flop count, size of factor matrices and elapsed run time for matrix factorization are reduced dramatically by using BLR representations and can go down to, respectively, 10, 30 and 40 per cent of their full-rank values for our largest system with N = 20.6 million unknowns. The reductions are almost independent of the number of MPI tasks and threads at least up to 90 × 10 = 900 cores. The BLR savings increase for larger systems, which reduces the factorization flop complexity from O(N 2 ) for the full-rank solver to O(N m ) with m = 1.4-1.6. The BLR savings are significantly larger for deep-water environments that exclude the highly resistive air layer from the computational domain. A study in a scenario where simulations are required at multiple source locations shows that the BLR solver can become competitive in comparison to iterative solvers as an engine for 3-D controlled-source electromagnetic Gauss-Newton inversion that requires forward modelling for a few thousand right-hand sides.

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“…; Endo, Cuma and Zhdanov ; Puzyrev et al . ; Jahandari and Farquharson ; Jaysaval et al., ; Kordy et al . ; Cai et al .…”

Section: Introductionunclassified

A finite‐element time‐domain forward‐modelling algorithm for transient electromagnetics excited by grounded‐wire sources

Cai

et al. 2020

Geophysical Prospecting

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A B S T R A C TA three-dimensional finite-element time-domain forward-modelling algorithm is developed to simulate transient electromagnetics excited by grounded-wire sources. The main advantage of this finite-element time-domain algorithm is that full transmitting-current waveforms and complex-shaped sources resulting from topography can be directly dealt with in this algorithm. The models used to test this algorithm include a homogeneous half-space model, a stratified-medium model, the model of a complex conductor at a vertical contact and the Ovoid Zone massive sulfide deposit at Voisey's Bay, Canada. The homogeneous half-space model is used to determine the truncation boundary for a computational domain, and to compare with the electromagnetic responses excited by step-off, step-on and direct current waveforms. For the stratified-medium model, results demonstrate that full transmitting waveforms have strong effects on the observed electromagnetic responses. The model of a complex conductor at a vertical contact is designed for the grounded electrical source airborne transient electromagnetic method and is also used to examine the effectiveness of the broadside and inline configurations for such a vertical, thin plate embedded in the subsurface. The area of the Ovoid Zone massive sulfide deposit possesses non-negligible topography, the effects of which on the shapes of the grounded-wire sources must be taken into account when implementing the finite-element time-domain solver. The results show that both the broadside and inline electromagnetic responses are strongly affected by the massive conductive ore body.

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Efficient 3-D controlled-source electromagnetic modelling using an exponential finite-difference method

Cited by 13 publications

References 33 publications

Stratigraphic Identification with Airborne Electromagnetic Methods at the Hanford Site, Washington

Stratigraphic Identification with Airborne Electromagnetic Methods at the Hanford Site, Washington

Large-scale 3-D EM modelling with a Block Low-Rank multifrontal direct solver

A finite‐element time‐domain forward‐modelling algorithm for transient electromagnetics excited by grounded‐wire sources

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