ModEM: A modular system for inversion of electromagnetic geophysical data

Kelbert, Anna; Meqbel, Naser; Egbert, G. D.; Tandon, Kush

doi:10.1016/j.cageo.2014.01.010

Cited by 605 publications

(295 citation statements)

References 32 publications

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“…The forward response of the synthetic model at the 28 sites located along the north-south profile, covering a range of periods between 0.0001 and 1000 s (frequencies of 10 000-0.001 Hz), was calculated using the ModEM code (Egbert & Kelbert 2012;Kelbert et al 2014), modified for inclusion on H responses (see Fig. S1, for more details), with a large 3-D mesh that comprised 222 × 182 × 132 cells in the north-south, east-west and vertical directions, respectively.…”

Section: Synthetic Modelmentioning

confidence: 99%

“…Nine inversions were performed using different combinations of Z, Z o , H and T responses employing the ModEM algorithm (Egbert & Kelbert 2012;Kelbert et al 2014) modified for inclusion on H responses (see Fig. S1, for more details).…”

Section: -D Inversion Of the Mt Profilementioning

confidence: 99%

“…11 plotting the summed nRMS as calculated in the ModEM code (Egbert & Kelbert 2012;Kelbert et al 2014) for each site, type of response and for each type of inversion, providing valuable information on how data misfit distributes along the profile for different inversions and different response types. Different colours were used for each type of response: red for Z o responses, black for Z responses, blue for T responses, and green for H responses.…”

Section: Fit Of the Datamentioning

confidence: 99%

“…In recent years, the availability of 3-D forward and inversion codes (e.g. Farquharson et al 2002;Siripunvaraporn et al 2005a;Avdeev & Avdeeva 2009;Egbert & Kelbert 2012;Kelbert et al 2014;Grayver 2015;Usui 2015) has improved the characterization of the subsurface in these situations, and 3-D inversion has become a more routine procedure for the EM community, although more experience is needed before it becomes as firmly established as is 2-D inversion (e.g. Miensopust et al 2013;Tietze & Ritter 2013;Kiyan et al 2014).…”

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confidence: 99%

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The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

Campanyà¹,

Ogaya²,

Jones³

et al. 2016

Geophys. J. Int.

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: The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study. -Geophysical Journal International, 207, 3, pp. 1818-1836 S U M M A R YAs a consequence of measuring time variations of the electric and the magnetic field, which are related to current flow and charge distribution, magnetotelluric (MT) data in 2-D and 3-D environments are not only sensitive to the geoelectrical structures below the measuring points but also to any lateral anomalies surrounding the acquisition site. This behaviour complicates the characterization of the electrical resistivity distribution of the subsurface, particularly in complex areas. In this manuscript we assess the main advantages of complementing the standard MT impedance tensor (Z) data with interstation horizontal magnetic tensor (H) and geomagnetic transfer function (T) data in constraining the subsurface in a 3-D environment beneath a MT profile. Our analysis was performed using synthetic responses with added normally distributed and scattered random noise. The sensitivity of each type of data to different resistivity anomalies was evaluated, showing that the degree to which each site and each period is affected by the same anomaly depends on the type of data. A dimensionality analysis, using Z, H and T data, identified the presence of the 3-D anomalies close to the profile, suggesting a 3-D approach for recovering the electrical resistivity values of the subsurface. Finally, the capacity for recovering the geoelectrical structures of the subsurface was evaluated by performing joint inversion using different data combinations, quantifying the differences between the true synthetic model and the models from inversion process. Four main improvements were observed when performing joint inversion of Z, H and T data: (1) superior precision and accuracy at characterizing the electrical resistivity values of the anomalies below and outside the profile; (2) the potential to recover high electrical resistivity anomalies that are poorly recovered using Z data alone; (3) improvement in the characterization of the bottom and lateral boundaries of the anomalies with low electrical resistivity; and (4) superior imaging of the horizontal continuity of structures with low electrical resistivity. These advantages offer new opportunities for the MT method by making the results from a MT profile in a 3-D environment more convincing, supporting the possibility of high-resolution studies in 3-D areas without expending a large amount of economical and computational resources, and also offering better resolution of targets with high electrical resistivity.

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Section: Synthetic Modelmentioning

confidence: 99%

Section: -D Inversion Of the Mt Profilementioning

confidence: 99%

Section: Fit Of the Datamentioning

confidence: 99%

mentioning

confidence: 99%

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The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

Campanyà¹,

Ogaya²,

Jones³

et al. 2016

Geophys. J. Int.

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“…For 3-D inversion, we used the Modular System (ModEM) of Egbert & Kelbert (2012) and Kelbert et al (2014) with additions for parallel computing described by Meqbel (2009). ModEM is based on a finite-difference (FD) approach to solve Maxwell's equations on a staggered grid.…”

Section: -D I N V E R S I O N a N D M O D E L L I N Gmentioning

confidence: 99%

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

et al. 2016

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S U M M A R YWe report on a study to explore the deep electrical conductivity structure of the Dead Sea Basin (DSB) using magnetotelluric (MT) data collected along a transect across the DSB where the left lateral strike-slip Dead Sea transform (DST) fault splits into two fault strands forming one of the largest pull-apart basins of the world. A very pronounced feature of our 2-D inversion model is a deep, subvertical conductive zone beneath the DSB. The conductor extends through the entire crust and is sandwiched between highly resistive structures associated with Precambrian rocks of the basin flanks. The high electrical conductivity could be attributed to fluids released by dehydration of the uppermost mantle beneath the DSB, possibly in combination with fluids released by mid-to low-grade metamorphism in the lower crust and generation of hydrous minerals in the middle crust through retrograde metamorphism. Similar high conductivity zones associated with fluids have been reported from other large fault systems. The presence of fluids and hydrous minerals in the middle and lower crust could explain the required low friction coefficient of the DST along the eastern boundary of the DSB and the high subsidence rate of basin sediments. 3-D inversion models confirm the existence of a subvertical high conductivity structure underneath the DSB but its expression is far less pronounced. Instead, the 3-D inversion model suggests a deepening of the conductive DSB sediments off-profile towards the south, reaching a maximum depth of approximately 12 km, which is consistent with other geophysical observations. At shallower levels, the 3-D inversion model reveals salt diapirism as an upwelling of highly resistive structures, localized underneath the Al-Lisan Peninsula. The 3-D model furthermore contains an E-W elongated conductive structure to the northeast of the DSB. More MT data with better spatial coverage are required, however, to fully constrain the robustness of the above-mentioned off-profile features.

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Ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data

2015

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Long‐period global‐scale electromagnetic induction studies of deep Earth conductivity are based almost exclusively on magnetovariational methods and require accurate models of external source spatial structure. We describe approaches to inverting for both the external sources and three‐dimensional (3‐D) conductivity variations and apply these methods to long‐period (T≥1.2 days) geomagnetic observatory data. Our scheme involves three steps: (1) Observatory data from 60 years (only partly overlapping and with many large gaps) are reduced and merged into dominant spatial modes using a scheme based on frequency domain principal components. (2) Resulting modes are inverted for corresponding external source spatial structure, using a simplified conductivity model with radial variations overlain by a two‐dimensional thin sheet. The source inversion is regularized using a physically based source covariance, generated through superposition of correlated tilted zonal (quasi‐dipole) current loops, representing ionospheric source complexity smoothed by Earth rotation. Free parameters in the source covariance model are tuned by a leave‐one‐out cross‐validation scheme. (3) The estimated data modes are inverted for 3‐D Earth conductivity, assuming the source excitation estimated in step 2. Together, these developments constitute key components in a practical scheme for simultaneous inversion of the catalogue of historical and modern observatory data for external source spatial structure and 3‐D Earth conductivity.

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ModEM: A modular system for inversion of electromagnetic geophysical data

Cited by 605 publications

References 32 publications

The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

The advantages of complementing MT profiles in 3-D environments with geomagnetic transfer function and interstation horizontal magnetic transfer function data: results from a synthetic case study

Crustal metamorphic fluid flux beneath the Dead Sea Basin: constraints from 2-D and 3-D magnetotelluric modelling

Ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data

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