Application of 3-D Electromagnetic Inversion in Practice: Challenges, Pitfalls and Solution Approaches

Miensopust, M. P.

doi:10.1007/s10712-017-9435-1

Cited by 58 publications

(31 citation statements)

References 190 publications

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“…The best-fit model (model S2) is shown in Figs 10 and 11 (see Table 1 The single RMS value of the best fitting model is not sufficient to judge its quality (Tietze & Ritter 2013;Miensopust 2017). Instead, the results were evaluated based on the convergence (see Fig.…”

Section: Stage Ii: 3-d Large-scale Inversionmentioning

confidence: 99%

Magnetotelluric multiscale 3-D inversion reveals crustal and upper mantle structure beneath the Hangai and Gobi-Altai region in Mongolia

Käufl

Grayver

Comeau

et al. 2020

Geophysical Journal International

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SUMMARY Central Mongolia is a prominent region of intracontinental surface deformation and intraplate volcanism. To study these processes, which are poorly understood, we collected magnetotelluric (MT) data in the Hangai and Gobi-Altai region in central Mongolia and derived the first 3-D resistivity model of the crustal and upper mantle structure in this region. The geological and tectonic history of this region is complex, resulting in features over a wide range of spatial scales, which that are coupled through a variety of geodynamic processes. Many Earth properties that are critical for the understanding of these processes, such as temperature as well as fluid and melt properties, affect the electrical conductivity in the subsurface. 3-D imaging using MT can resolve the distribution of electrical conductivity within the Earth at scales ranging from tens of metres to hundreds of kilometres, thereby providing constraints on possible geodynamic scenarios. We present an approach to survey design, data acquisition, and inversion that aims to bridge various spatial scales while keeping the required field work and computational cost of the subsequent 3-D inversion feasible. MT transfer functions were estimated for a 650 × 400 km2 grid, which included measurements on an array with regular 50 × 50 km2 spacing and along several profiles with a denser 5–15 km spacing. The use of telluric-only data loggers on these profiles allowed for an efficient data acquisition with a high spatial resolution. A 3-D finite element forward modelling and inversion code was used to obtain the resistivity model. Locally refined unstructured hexahedral meshes allow for a multiscale model parametrization and accurate topography representation. The inversion process was carried out over four stages, whereby the result from each stage was used as input for the following stage that included a finer model parametrization and/or additional data (i.e. more stations, wider frequency range). The final model reveals a detailed resistivity structure and fits the observed data well, across all periods and site locations, offering new insights into the subsurface structure of central Mongolia. A prominent feature is a large low-resistivity zone detected in the upper mantle. This feature suggests a non-uniform lithosphere-asthenosphere boundary that contains localized upwellings that shallow to a depth of 70 km, consistent with previous studies. The 3-D model reveals the complex geometry of the feature, which appears rooted below the Eastern Hangai Dome with a second smaller feature slightly south of the Hangai Dome. Within the highly resistive upper crust, several conductive anomalies are observed. These may be explained by late Cenozoic volcanic zones and modern geothermal areas, which appear linked to mantle structures, as well as by major fault systems, which mark terrane boundaries and mineralized zones. Well resolved, heterogeneous low-resistivity zones that permeate the lower crust may be explained by fluid-rich domains.

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Section: Stage Ii: 3-d Large-scale Inversionmentioning

confidence: 99%

Magnetotelluric multiscale 3-D inversion reveals crustal and upper mantle structure beneath the Hangai and Gobi-Altai region in Mongolia

Käufl

Grayver

Comeau

et al. 2020

Geophysical Journal International

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“…A thorough overview of how data errors, data components inverted and grid rotation affect 3D inversion has been conducted by Tietze and Ritter (2013), and a recent review of 3D modelling in practice by Miensopust (2017) exists, along with an investigation into some ModEM3DMT parameters (Slezak et al 2019); however, as of yet, an in-depth overview of the many other modelling parameters that affect the resultant model is not available, and some of these will be investigated throughout this manuscript, specific to the 3D inversion code, ModEM3DMT.…”

Section: Introductionmentioning

confidence: 99%

Quality over quantity: on workflow and model space exploration of 3D inversion of MT data

Robertson

Thiel

Meqbel

2020

Earth Planets Space

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3D inversions of magnetotelluric data are now almost standard, with computational power now allowing an inversion to be performed in a matter of days (or hours) rather than weeks. However, when compared to 2D inversions, these are still very computationally demanding. As a result, 3D inversions are generally not subjected to as rigorous testing as a 1D or 2D inversion would be, which has implications when these models are used for geological interpretation. In this study, we explore the parameter space for inversion of continent-scale datasets. The generalisations made regarding the effects of each parameter should also be scalable to smaller surveys and will enable MT practitioners to optimise their results. We have performed testing on a subset of the South Australian component of the eventual Australia-wide AusLAMP (Australian Lithospheric Architecture Magnetotelluric Project). The subset was inverted with different parameters, model setup and data subsets. Specifically, results from testing of the model covariance, the resistivity of the prior model, the inclusion of 'known' information into the prior model, the model cell size, the data components inverted for and the damping parameter were all investigated. In our testing of the 3D inversion software, ModEM3DMT, we found that the resistivity of the starting/prior model had significant effect on the final model. Careful selection of initial value can aid in reducing computational time whilst having a negligible effect on the resultant model, whilst large covariance values and model cell sizes enhanced conductive features at depth.

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“…The spatial smoothing parameter δy was increased from 0.1 to 0.5. A larger spatial smoothing parameter promotes smoothing and longer structures along that direction (Miensopust, ). The RMS variations of the iterations are shown in Figures b–d.…”

Section: Robustness Evaluation Of Features In the Resistivity Modelsmentioning

confidence: 99%

Lateral Rheology Differences in the Lithosphere and Dynamics as Revealed by Magnetotelluric Imaging at the Northern Tibetan Plateau

Xiao

Shao

et al. 2018

JGR Solid Earth

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Differences in topography and surface deformation in the northern Tibetan Plateau may reflect variable rheology in the lithosphere. Whether middle to lower crustal flow exists below the region between the eastern Kunlun Shan range and the Qaidam Basin remains debated. We provide electrical resistivity images of three new magnetotelluric (MT) profiles across the Qiman Tagh and the western Qaidam Basin. The new models reveal low‐resistivity anomalies below the Qaidam Basin in the lower crust and generally high‐resistivity crust in the Qiman Tagh range. A low‐resistivity anomaly at the uppermost‐mantle level is imaged below the Qiman Tagh range in the profile close to the Altyn Tagh Fault. This anomaly is possibly connected with partial melting in the lower portion of the thickened Songpan‐Ganzi crust close to the southern end of the study area; the minimum requirements for the low‐resistivity anomaly below the Qiman Tagh are 0.05 wt% water content or 0.02 melt fraction, which may greatly decrease the effective viscosity in the uppermost‐mantle rocks and allow flowing. Consequently, we propose that the crustal flow is not mature below the Kunlun Shan range south of the Qaidam Basin because no continuous and stable low‐resistivity anomaly was imaged at this level. The uppermost‐mantle low‐resistivity anomaly below the Qiman Tagh is a passage that allows the continuous northward transfer of materials in the interior of the plateau. This low‐resistivity channel shallows northward and reaches the lower crust of the southwestern Qaidam Basin.

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Application of 3-D Electromagnetic Inversion in Practice: Challenges, Pitfalls and Solution Approaches

Cited by 58 publications

References 190 publications

Magnetotelluric multiscale 3-D inversion reveals crustal and upper mantle structure beneath the Hangai and Gobi-Altai region in Mongolia

Magnetotelluric multiscale 3-D inversion reveals crustal and upper mantle structure beneath the Hangai and Gobi-Altai region in Mongolia

Quality over quantity: on workflow and model space exploration of 3D inversion of MT data

Lateral Rheology Differences in the Lithosphere and Dynamics as Revealed by Magnetotelluric Imaging at the Northern Tibetan Plateau

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