8. The Magnetotelluric Method

Vozoff, K.

doi:10.1190/1.9781560802686.ch8

Cited by 381 publications

(281 citation statements)

References 62 publications

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“…Vozoff 1991). To better understand which structures are required by a particular data component, we also show 3-D inversion results for Z and Tz separately.…”

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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“…Vozoff 1991). To better understand which structures are required by a particular data component, we also show 3-D inversion results for Z and Tz separately.…”

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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“…Vozoff 1991;Berdichevsky et al 1998;Bedrosian 2007;Berdichevsky & Dmitriev 2008;Chave & Jones 2012;Miensopust et al 2013). The capacity at recovering low electrical resistivity structures is a particular strength of the MT method as a geophysical technique when characterizing geoelectrical structures from the first few metres to the asthenosphere (e.g.…”

mentioning

confidence: 99%

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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“…The following summary is a distillation of 5 decades of work by many scientists in the MT field; good reviews are given by Vozoff [1991] or Nabighian [1991]. Small (1:50,000,000 of the Earth's total field) variations of the magnetic field induce electrical currents in the Earth.…”

Section: Mt Methodsmentioning

confidence: 99%

“…The magnitude is converted to an apparent resistivity that is equal to the true resistivity only when the earth is homogeneous [Vozoff, 1991]. Otherwise, the apparent resistivity is transformed to true resistivity (which is the inverse of conductivity) through a process called inversion.…”

Section: Mt Methodsmentioning

confidence: 99%

Electrical conductivity images of Quaternary faults and Tertiary detachments in the California Basin and Range

Park

Wernicke

2003

Tectonics

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Comparison of an electrical resistivity section derived from magnetotelluric (MT) data to a geologic section extending eastward from the Sierra Nevada near latitude 36°20′N shows that the crust is dominated by steeply dipping conductive features that correlate with active strike‐slip faults. While there is a subhorizontal conductor at a depth ∼20 km beneath some of the profile, it is broken by vertical structures associated with the active strike‐slip faults. The continuous subhorizontal anomalies in the lower crust typically observed in extensional regions are therefore absent in the resistivity section. The present‐day strike‐slip tectonic regime as indicated by geodetic data in this part of the Basin and Range is not producing features that could be inferred to indicate subhorizontal shear zones resulting from lateral crustal flow during extension. Because the Miocene tectonic regime resulted in the formation of metamorphic core complexes and thus was accompanied by such flow, the present regime appears to represent a fundamental transition in the mode of crustal deformation in the region. A serendipitous result of our study was the identification on resistivity sections of carbonate aquifers in the upper crust. Comparison of resistivities from the MT section to measured fluid resistivities from springs and boreholes suggests that the aquifers must be heterogeneous, with more saline brines occupying the deepest portions of the carbonates.

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8. The Magnetotelluric Method

Cited by 381 publications

References 62 publications

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

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

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

Electrical conductivity images of Quaternary faults and Tertiary detachments in the California Basin and Range

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