Linking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor

Abstract Estimation of the traditional transverse electric (TE) and transverse magnetic (TM) impedances of the magnetotelluric tensor for two-dimensional structures can be decoupled from the estimation of the strike direction with significant implications when dealing with galvanic distortions. Dist...

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Autores principales:	Rocío F. Arellano-Castro, Enrique Gómez-Treviño
Formato:	article
Lenguaje:	EN
Publicado:	SpringerOpen 2021
Materias:	Strike direction Invariants TE and TM Phase tensor Quadratic equation Geography. Anthropology. Recreation G Geodesy QB275-343 Geology QE1-996.5
Acceso en línea:	https://doaj.org/article/e6eca50fb88b473c91a8dd005a384299
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spelling	oai:doaj.org-article:e6eca50fb88b473c91a8dd005a3842992021-11-14T12:30:48ZLinking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor10.1186/s40623-021-01538-61880-5981https://doaj.org/article/e6eca50fb88b473c91a8dd005a3842992021-11-01T00:00:00Zhttps://doi.org/10.1186/s40623-021-01538-6https://doaj.org/toc/1880-5981Abstract Estimation of the traditional transverse electric (TE) and transverse magnetic (TM) impedances of the magnetotelluric tensor for two-dimensional structures can be decoupled from the estimation of the strike direction with significant implications when dealing with galvanic distortions. Distortion-free data are obtainable by combining a quadratic equation with the phase tensor. In the terminology of Groom–Bailey, the quadratic equation provides amplitudes and phases that are immune to twist, and the phase tensor provides phases immune to both, twist and shear. On the other hand, distortion-free strike directions can be obtained using Bahr's approach or the phase tensor. In principle, this is all that is needed to proceed to a two-dimensional (2D) interpretation. However, the resulting impedances are strike ignorant because they are invariant under coordinate system rotation, and if they are to be related to a geological strike, they must be linked to a particular direction. This is an additional ambiguity to the one of 90° arising in classic strike-determination methods, which must be resolved independently. In this work, we use the distortion model of Groom–Bailey to resolve the ambiguity by bringing back the coupling between impedances and strike in the presence of galvanic distortions. Our approach is a hybrid between existing numerical and analytical methods that reduces the problem to a binary decision, which involves associating the invariant impedances with the correct TE and TM modes. To determine the appropriate association, we present three algorithms. Two of them require optimizing the fit to the data, and the third one requires a comparison of phases. All three keep track of possible crossings of the phase curves providing a clear-cut solution. Synthetic and field data illustrate the performance of the three schemes. Graphical AbstractRocío F. Arellano-CastroEnrique Gómez-TreviñoSpringerOpenarticleStrike directionInvariants TE and TMPhase tensorQuadratic equationGeography. Anthropology. RecreationGGeodesyQB275-343GeologyQE1-996.5ENEarth, Planets and Space, Vol 73, Iss 1, Pp 1-16 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Strike direction Invariants TE and TM Phase tensor Quadratic equation Geography. Anthropology. Recreation G Geodesy QB275-343 Geology QE1-996.5
spellingShingle	Strike direction Invariants TE and TM Phase tensor Quadratic equation Geography. Anthropology. Recreation G Geodesy QB275-343 Geology QE1-996.5 Rocío F. Arellano-Castro Enrique Gómez-Treviño Linking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor
description	Abstract Estimation of the traditional transverse electric (TE) and transverse magnetic (TM) impedances of the magnetotelluric tensor for two-dimensional structures can be decoupled from the estimation of the strike direction with significant implications when dealing with galvanic distortions. Distortion-free data are obtainable by combining a quadratic equation with the phase tensor. In the terminology of Groom–Bailey, the quadratic equation provides amplitudes and phases that are immune to twist, and the phase tensor provides phases immune to both, twist and shear. On the other hand, distortion-free strike directions can be obtained using Bahr's approach or the phase tensor. In principle, this is all that is needed to proceed to a two-dimensional (2D) interpretation. However, the resulting impedances are strike ignorant because they are invariant under coordinate system rotation, and if they are to be related to a geological strike, they must be linked to a particular direction. This is an additional ambiguity to the one of 90° arising in classic strike-determination methods, which must be resolved independently. In this work, we use the distortion model of Groom–Bailey to resolve the ambiguity by bringing back the coupling between impedances and strike in the presence of galvanic distortions. Our approach is a hybrid between existing numerical and analytical methods that reduces the problem to a binary decision, which involves associating the invariant impedances with the correct TE and TM modes. To determine the appropriate association, we present three algorithms. Two of them require optimizing the fit to the data, and the third one requires a comparison of phases. All three keep track of possible crossings of the phase curves providing a clear-cut solution. Synthetic and field data illustrate the performance of the three schemes. Graphical Abstract
format	article
author	Rocío F. Arellano-Castro Enrique Gómez-Treviño
author_facet	Rocío F. Arellano-Castro Enrique Gómez-Treviño
author_sort	Rocío F. Arellano-Castro
title	Linking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor
title_short	Linking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor
title_full	Linking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor
title_fullStr	Linking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor
title_full_unstemmed	Linking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor
title_sort	linking strike directions to invariant te and tm impedances of the magnetotelluric impedance tensor
publisher	SpringerOpen
publishDate	2021
url	https://doaj.org/article/e6eca50fb88b473c91a8dd005a384299
work_keys_str_mv	AT rociofarellanocastro linkingstrikedirectionstoinvariantteandtmimpedancesofthemagnetotelluricimpedancetensor AT enriquegomeztrevino linkingstrikedirectionstoinvariantteandtmimpedancesofthemagnetotelluricimpedancetensor
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Linking strike directions to invariant TE and TM impedances of the magnetotelluric impedance tensor

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