Three-dimensional inversion of magnetotelluric phase tensor data

Patro, Prasanta K.; Uyeshima, Makoto; Siripunvaraporn, Weerachai

doi:10.1093/gji/ggs014

Cited by 42 publications

(34 citation statements)

References 16 publications

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“…Thus, when inverting these data, particular care has to be taken of the conductivity structure in the a priori model, which provides the reference frame when transferring the information from phase tensors into absolute conductivity values (cf. Patro et al 2013). We implemented 3-D inversion of the PT into the ModEM software package Kelbert et al 2014).…”

Section: -D Magnetotelluric Inversion Techniquesmentioning

confidence: 99%

“…We implemented 3-D inversion of the PT into the ModEM software package Kelbert et al 2014). Our PT inversion approach is similar to that of Patro et al (2013) who appended inversion of the phase tensor to the WSINV3DMT code of Siripunvaraporn et al (2005). Moreover, ModEM allows joint inversion of PT data and VTFs which are also free of galvanic distortion.…”

Section: -D Magnetotelluric Inversion Techniquesmentioning

confidence: 99%

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3-D joint inversion of the magnetotelluric phase tensor and vertical magnetic transfer functions

Tietze¹,

Ritter²,

Egbert³

2015

Geophys. J. Int.

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S U M M A R YWith advancing computational resources, 3-D inversion techniques have become feasible in recent years and are now a more widely used tool for magnetotelluric (MT) data interpretation. Galvanic distortion caused by small-scale near-surface inhomogeneities remains an obstacle for 3-D MT inversion which so far has experienced little attention. If not considered properly, the effect on 3-D inversion can be immense and result in erroneous subsurface models and interpretations. To tackle the problem we implemented inversion of the distortion-free phase tensor into the ModEM inversion package. The dimensionless phase tensor components describe only variations of the conductivity structure. When inverting these data, particular care has to be taken of the conductivity structure in the a priori model, which provides the reference frame when transferring the information from phase tensors into absolute conductivity values. Our results obtained with synthetic data show that phase tensor inversion can recover the regional conductivity structure in presence of galvanic distortion if the a priori model provides a reasonable assumption for the regional resistivity average. Joint inversion of phase tensor data and vertical magnetic transfer functions improves recovery of the absolute resistivity structure and is less dependent on the prior model. We also used phase tensor inversion for a data set of more than 250 MT sites from the central San Andreas fault, California, where a number of sites showed significant galvanic distortion. We find the regional structure of the phase tensor inversion results compatible with previously obtained models from impedance inversion. In the vicinity of distorted sites, phase tensor inversion models exhibit more homogeneous/smoother conductivity structures.

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Section: -D Magnetotelluric Inversion Techniquesmentioning

confidence: 99%

Section: -D Magnetotelluric Inversion Techniquesmentioning

confidence: 99%

3-D joint inversion of the magnetotelluric phase tensor and vertical magnetic transfer functions

Tietze¹,

Ritter²,

Egbert³

2015

Geophys. J. Int.

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“…Inversion based on the phase tensor (Caldwell et al 2004), which yields a well-defined distortion-free solution, is also a promising strategy. However, the phase tensor is only a partial solution; thus, the inverted model strongly depends on the initial model (Patro et al 2013;Tietze et al 2015). In addition to decomposition approaches, inversion schemes that simultaneously solve the static shift (e.g., Sasaki and Meju 2006) have become feasible, but the geometric distortion is not controlled.…”

Section: )mentioning

confidence: 99%

Use of ssq rotational invariant of magnetotelluric impedances for estimating informative properties for galvanic distortion

Rung-Arunwan

Siripunvaraporn

Utada

2017

Earth Planets Space

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Several useful properties and parameters-a model of the regional mean one-dimensional (1D) conductivity profile, local and regional distortion indicators, and apparent gains-were defined in our recent paper using two rotational invariants (det: determinant and ssq: sum of squared elements) from a set of magnetotelluric (MT) data obtained by an array of observation sites. In this paper, we demonstrate their characteristics and benefits through synthetic examples using 1D and three-dimensional (3D) models. First, a model of the regional mean 1D conductivity profile is obtained using the average ssq impedance with different levels of galvanic distortion. In contrast to the Berdichevsky average using the average det impedance, the average ssq impedance is shown to yield a reliable estimate of the model of the regional mean 1D conductivity profile, even when severe galvanic distortion is contained in the data. Second, the local and regional distortion indicators were found to indicate the galvanic distortion as expressed by the splitting and shear parameters and to quantify their strengths in individual MT data and in the dataset as a whole. Third, the apparent gain was also shown to be a good approximation of the site gain, which is generally claimed to be undeterminable without external information. The model of the regional mean 1D profile could be used as an initial or a priori model in higher-dimensional inversions. The local and regional distortion indicators and apparent gains could be used to examine the existence and to guess the strength of the galvanic distortion. Although these conclusions were derived from synthetic tests using the Groom-Bailey distortion model, additional tests with different distortion models indicated that these conclusions are not strongly dependent on the choice of distortion model. These galvanic-distortion-related parameters would also assist in judging if a proper treatment is needed for the galvanic distortion when an MT dataset is given. Hence, this information derived from the dataset would be useful in MT data analysis and inversion.

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“…7. The uncertainties of the elements of phase tensors were calculated using the delta method (Patro et al 2013;Booker 2014), which is a standard method for propagating variables' uncertainties (or errors) to the uncertainties of functions based on them (Ver Hoef 2012). A summary of the mathematics behind the delta method is given in Appendix 1, and in Appendix 2, explicit formulas for the calculation of the uncertainties for the elements of the phase tensors are given.…”

Section: Calculating (Quasi-) Electric Phase Tensors From a Field Datmentioning

confidence: 99%

Introducing inter-site phase tensors to suppress galvanic distortion in the telluric method

et al. 2015

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A common problem when interpreting magnetotelluric (MT) data is that they often are distorted by shallow unresolvable local structures, an effect known as galvanic distortion. We present two transfer functions that are (almost) resistant to galvanic distortion. First, we introduce the electric phase tensor, which is derived from the electric tensor, where the electric tensor relates the horizontal electric fields at a field and base site. The electric phase tensor is only affected by galvanic distortion, if present, at the base site. Second, we introduce the quasi-electric phase tensor, which is derived from the quasi-electric tensor, where the quasi-electric tensor relates the electric field at a field site with the magnetic field at a base site. The quasi-electric tensor is not affected by galvanic distortion. Using a synthetic data-set, we show that the sensitivity of the MT phase tensor, the quasi-electric phase tensor, and the electric phase tensor is comparable for our model under consideration. Furthermore, we demonstrate that stable (quasi-) electric phase tensors can be recovered from a real data-set with the use of existing processing software. In addition, we provide a formalism to propagate the uncertainties from the estimated (quasi-) electric and impedance tensors to their respective phase tensors. The uncertainties of the (quasi-) electric phase tensors are of the same order of magnitude as the uncertainties of the MT phase tensor. From our study, we conclude that the (quasi-) electric phase tensors are an attractive complement to the standard MT responses.

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Three-dimensional inversion of magnetotelluric phase tensor data

Cited by 42 publications

References 16 publications

3-D joint inversion of the magnetotelluric phase tensor and vertical magnetic transfer functions

3-D joint inversion of the magnetotelluric phase tensor and vertical magnetic transfer functions

Use of ssq rotational invariant of magnetotelluric impedances for estimating informative properties for galvanic distortion

Introducing inter-site phase tensors to suppress galvanic distortion in the telluric method

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