Nonlinear conjugate gradients algorithm for 2-D magnetotelluric inversion

Rodi, William; Mackie, Randall L.

doi:10.1190/1.1444893

Cited by 1,169 publications

(666 citation statements)

References 32 publications

Supporting

Mentioning

641

Contrasting

Unclassified

Order By: Relevance

“…The relative weight given to the data fit and the model smoothness can be controlled by a trade-off parameter (τ), which controls the inversion result (Rodi and Mackie, 2001). In other words, τ can be viewed as a sensitivity parameter, which essentially controls the RMS value between the data and the model.…”

Section: Two-dimensional Mt Inversionmentioning

confidence: 99%

“…TE and TM modes data (apparent resistivity and phase) were subjected to regularized 2D inversion of Rodi and Mackie (2001) for a frequency range of 1030-0.01 Hz, along the three profiles, AA , BB and CC in Fig. 1.…”

Section: Two-dimensional Mt Inversionmentioning

confidence: 99%

“…Static shift corrections on MT data were performed as part of the inversion process following the approach of Rodi and Mackie (2001). de Groot-Hedlin (1991) suggested that static shifts may be treated as unknown free parameters during inversion.…”

Section: Mt Data Acquisition and Processingmentioning

confidence: 99%

See 2 more Smart Citations

An integrated magnetotelluric and aeromagnetic investigation of the Serra da Cangalha impact crater, Brazil

Adepelumi

Fontes

Schnegg

et al. 2005

Physics of the Earth and Planetary Interiors

View full text Add to dashboard Cite

The research is aimed at delineating the post-impact structural characteristics across the Serra da Cangalha impact crater in Brazil using a combination of magnetotelluric (MT) and aeromagnetic data. The MT survey was carried out along three radial MT profiles trending NW-SE, ENE-WSW and NNE-SSW across the crater. For MT sites located further away from the centre of the crater, isotropic MT responses were observed, suggesting a 1D conductivity distribution in the subsurface in the frequency range of 100-10 Hz. For sites located in the vicinity of the inner ring of the crater, anisotropic responses were observed for the same frequency range. We believe that this zone probably represents the areas of structural disturbance. A 2D resistivity inversion of these data reveals a four-layer model, representing a thin resistive layer underlain by a conductive layer, a weathered basement and a resistive crystalline basement. The depth to the top of the basement is estimated to be about 1.2 km. This is in good agreement with the estimation of depth to the basement of about 1.1 km, calculated using the aeromagnetic data. However, in view of the circular geometry of the crater, we have carried out a 3D forward modeling computation to supplement the derived 2D model. The 3D resistivity forward model, fitting the MT responses by trial-by-error revealed a five-layer model, showing a significant reduction in the basement resistivity. This, perhaps, could be due to the structural disturbances that have been caused by the impact on the crater, resulting in brecciation, fracturing, alteration and shocked zone filled with weak-magnetic materials and fluids. We have calculated the effect of the impact on the overall structural deformation beneath the Serra da Cangalha crater, following the classical crater scaling relation of Holsapple and Schmidt [Holsapple, K.A., Schmidt, R.M., 1982

show abstract

Section: Two-dimensional Mt Inversionmentioning

confidence: 99%

Section: Two-dimensional Mt Inversionmentioning

confidence: 99%

See 1 more Smart Citation

An integrated magnetotelluric and aeromagnetic investigation of the Serra da Cangalha impact crater, Brazil

Adepelumi

Fontes

Schnegg

et al. 2005

Physics of the Earth and Planetary Interiors

View full text Add to dashboard Cite

show abstract

“…4, label D). For 2-D inversion, we used the regularized non-linear conjugate gradient (NLCG) algorithm described by Rodi & Mackie (2001). This algorithm is implemented in the WinGLink software package.…”

Section: -D I N V E R S I O N O F T H E M T Datamentioning

confidence: 99%

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

et al. 2016

View full text Add to dashboard Cite

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.

show abstract

“…where g = (Kα Kβ ) T , Kα and Kβ are the gradients found in eqs (9) and (10) and sorted into row vectors, C is a pre-conditioner (here we use it as a smoothing function), and scalar η i is defined as in for example, Rodi & Mackie (2001) as…”

Section: Derivation Of the Sicp-wemva Optimizationmentioning

confidence: 99%

Source-independent full wavefield converted-phase elastic migration velocity analysis

Shabelansky

Malcolm

Fehler

et al. 2014

Geophysical Journal International

View full text Add to dashboard Cite

S U M M A R YConverted phase (CP) elastic seismic signals are comparable in amplitude to the primary signals recorded at large offsets and have the potential to be used in seismic imaging and velocity analysis. We present an approach for CP elastic wave equation velocity analysis that does not use source information and is applicable to surface-seismic, microseismic, teleseismic and vertical seismic profile (VSP) studies. Our approach is based on the crosscorrelation between reflected or transmitted PP and CP PS (and/or SS and CP SP) waves propagated backward in time, and is formulated as an optimization problem with a differential semblance criterion objective function for the simultaneous update of both P-and S-wave velocity models. The merit of this approach is that it is fully data-driven, uses full waveform information, and requires only one elastic backward propagation to form an image rather than the two (one forward and one backward) propagations needed for standard reverse-time migration. Moreover, as the method does not require forward propagation, it does not suffer from migration operator source aliasing when a small number of shots are used. We present a derivation of the method and test it with a synthetic model and field micro-seismic data.Key words: Inverse theory; Body waves; Seismic tomography; Computational seismology; Wave propagation. I N T RO D U C T I O NIn recent years, full waveform seismic imaging and velocity analysis methods have become standard and the use of elastic waves is now drawing more attention. Converted phase (CP) waves are an integrated part of the recorded elastic seismic signal and are investigated in numerous studies in the research areas of vertical seismic profile (VSP) data (e.g. Esmersoy 1990; Stewart 1991; Xiao & Leaney 2010), surface reflection (e.g. Purnell 1992;Stewart et al. 2003;Hardage et al. 2011) and transmission seismic data (e.g. Vinnik 1977;Vinnik et al. 1983;Bostock et al. 2001;Rondenay et al. 2001;Brytic et al. 2012;Shang et al. 2012;Shabelansky et al. 2013). In particular, for example Xiao & Leaney (2010) and Shang et al. (2012) showed that the CP seismic images can be calculated using one elastic propagation without using source information (i.e. location, mechanism and time-function). Source information is generally considered mandatory in standard seismic imaging and velocity analysis. However, in * Now at: Earth Sciences Department, Memorial University of Newfound- passive monitoring source information is generally not available and in active source surveys seismic data require special treatment for frequency matching due to coupling differences between soil and vibro-seis or dynamite casing. These factors affect the accuracy of the imaging and velocity estimation and add computational and processing cost. Moreover, CP elastic seismic imaging is shown to have higher resolution in Xiao & Leaney (2010) and fewer artifacts than reflection type imaging in Shabelansky et al. (2012). In this study, we present a source-independent CP (SICP) velocity anal...

show abstract

Nonlinear conjugate gradients algorithm for 2-D magnetotelluric inversion

Cited by 1,169 publications

References 32 publications

An integrated magnetotelluric and aeromagnetic investigation of the Serra da Cangalha impact crater, Brazil

An integrated magnetotelluric and aeromagnetic investigation of the Serra da Cangalha impact crater, Brazil

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

Source-independent full wavefield converted-phase elastic migration velocity analysis

Contact Info

Product

Resources

About