Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents
Electromagnetic surface measurements with the radiomagnetotelluric (RMT) method in the frequency range between 10 and 300 kHz are typically interpreted in the quasi-static approximation, that is, assuming displacement currents are negligible. In this paper, the dielectric effect of displacement curr...
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th-mahidol.191742018-07-12T09:25:33Z Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents Thomas Kalscheuer Laust B. Pedersen Weerachai Siripunvaraporn Uppsala Universitet Mahidol University Earth and Planetary Sciences Electromagnetic surface measurements with the radiomagnetotelluric (RMT) method in the frequency range between 10 and 300 kHz are typically interpreted in the quasi-static approximation, that is, assuming displacement currents are negligible. In this paper, the dielectric effect of displacement currents on RMT responses over resistive subsurface models is studied with a 2-D forward and inverse scheme that can operate both in the quasi-static approximation and including displacement currents. Forward computations of simple models exemplify how responses that allow for displacement currents deviate from responses computed in the quasi-static approximation. The differences become most obvious for highly resistive subsurface models of about 3000Ωm and more and at high frequencies. For such cases, the apparent resistivities and phases of the transverse magnetic (TM) and transverse electric (TE) modes are significantly smaller than in the quasi-static approximation. Along profiles traversing 2-D subsurface models, sign reversals in the real part of the vertical magnetic transfer function (VMT) are often more pronounced than in the quasi-static approximation. On both sides of such sign reversals, the responses computed including displacement currents are larger than typical measurement errors. The 2-D inversion of synthetic data computed including displacement currents demonstrates that serious misinterpretations in the form of artefacts in inverse models can be made if displacement currents are neglected during the inversion. Hence, the inclusion of the dielectric effect is a crucial improvement over existing quasi-static 2-D inverse schemes. Synthetic data from a 2-D model with constant dielectric permittivity and a conductive block buried in a highly resistive layer, which in turn is underlain by a conductive layer, are inverted. In the quasi-static inverse model, the depth to the conductive structures is overestimated, artefactual resistors appear on both sides of the conductive block and a spurious conductive layer is imaged at the surface. High-frequency RMT field data from Ävrö, Sweden, arere-interpreted using the newly developed 2-D inversion scheme that includes displacement currents. In contrast to previous quasi-static modelling, the new inverse models have electrical resistivity values comparable to a normal-resistivity borehole log and boundaries between resistive and conductive structures, which correlate with the positions of seismic reflectors. © 2008 The Authors Journal compilation © 2008 RAS. 2018-07-12T02:25:33Z 2018-07-12T02:25:33Z 2008-10-31 Article Geophysical Journal International. Vol.175, No.2 (2008), 486-514 10.1111/j.1365-246X.2008.03902.x 1365246X 0956540X 2-s2.0-54849418630 https://repository.li.mahidol.ac.th/handle/123456789/19174 Mahidol University SCOPUS https://www.scopus.com/inward/record.uri?partnerID=HzOxMe3b&scp=54849418630&origin=inward |
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Earth and Planetary Sciences Thomas Kalscheuer Laust B. Pedersen Weerachai Siripunvaraporn Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents |
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Electromagnetic surface measurements with the radiomagnetotelluric (RMT) method in the frequency range between 10 and 300 kHz are typically interpreted in the quasi-static approximation, that is, assuming displacement currents are negligible. In this paper, the dielectric effect of displacement currents on RMT responses over resistive subsurface models is studied with a 2-D forward and inverse scheme that can operate both in the quasi-static approximation and including displacement currents. Forward computations of simple models exemplify how responses that allow for displacement currents deviate from responses computed in the quasi-static approximation. The differences become most obvious for highly resistive subsurface models of about 3000Ωm and more and at high frequencies. For such cases, the apparent resistivities and phases of the transverse magnetic (TM) and transverse electric (TE) modes are significantly smaller than in the quasi-static approximation. Along profiles traversing 2-D subsurface models, sign reversals in the real part of the vertical magnetic transfer function (VMT) are often more pronounced than in the quasi-static approximation. On both sides of such sign reversals, the responses computed including displacement currents are larger than typical measurement errors. The 2-D inversion of synthetic data computed including displacement currents demonstrates that serious misinterpretations in the form of artefacts in inverse models can be made if displacement currents are neglected during the inversion. Hence, the inclusion of the dielectric effect is a crucial improvement over existing quasi-static 2-D inverse schemes. Synthetic data from a 2-D model with constant dielectric permittivity and a conductive block buried in a highly resistive layer, which in turn is underlain by a conductive layer, are inverted. In the quasi-static inverse model, the depth to the conductive structures is overestimated, artefactual resistors appear on both sides of the conductive block and a spurious conductive layer is imaged at the surface. High-frequency RMT field data from Ävrö, Sweden, arere-interpreted using the newly developed 2-D inversion scheme that includes displacement currents. In contrast to previous quasi-static modelling, the new inverse models have electrical resistivity values comparable to a normal-resistivity borehole log and boundaries between resistive and conductive structures, which correlate with the positions of seismic reflectors. © 2008 The Authors Journal compilation © 2008 RAS. |
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Uppsala Universitet |
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Uppsala Universitet Thomas Kalscheuer Laust B. Pedersen Weerachai Siripunvaraporn |
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Article |
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Thomas Kalscheuer Laust B. Pedersen Weerachai Siripunvaraporn |
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Thomas Kalscheuer |
title |
Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents |
title_short |
Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents |
title_full |
Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents |
title_fullStr |
Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents |
title_full_unstemmed |
Radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents |
title_sort |
radiomagnetotelluric two-dimensional forward and inverse modelling accounting for displacement currents |
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2018 |
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https://repository.li.mahidol.ac.th/handle/123456789/19174 |
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1763493984038027264 |