3‐D magnetotelluric inversion for resource exploration

Mackie, Randall L.; Rodi, William; Watts, M. D.

doi:10.1190/1.1816392

Cited by 30 publications

(23 citation statements)

References 6 publications

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“…Alternatively, Newman and Alumbaugh (2000), Rodi and Mackie (2001) and Mackie et al (2001) proposed to solve the 3-D inverse problem using the nonlinear conjugate gradient method (NLCG) by Fletcher and Reeves (1964) and Polak and Ribiere (1969) that requires for computation only the gradient vectors g ¼ @u @m , rather than sensitivities J (see Appendix C for details). The idea of applying gradient vectors to solve nonlinear geophysical inverse problems was first suggested by Tarantola (1987) and is also related to the EM migration technique of Zhdanov (2002; and the references therein).…”

Section: How Is It Commonly Solved?mentioning

confidence: 99%

“…Such great acceleration is slightly counterbalanced by the fact that the NLCG approach requires the solution of the 1-D minimization problem (so-called line search) at each iteration. Rodi and Mackie (2001) proposed an algorithm for the line search, equivalent in computational time to only three solutions of the forward problem. In spite of such a dramatic increase in speed, the NLCG approach still has to be implemented either within a massively parallel computing architecture (Newman and Alumbaugh, 2000;Newman and Boggs, 2004) or with the help of message passing interface (MPI) running on PC-clusters (Mackie et al, 2001).…”

Section: How Is It Commonly Solved?mentioning

confidence: 99%

“…Rodi and Mackie (2001) proposed an algorithm for the line search, equivalent in computational time to only three solutions of the forward problem. In spite of such a dramatic increase in speed, the NLCG approach still has to be implemented either within a massively parallel computing architecture (Newman and Alumbaugh, 2000;Newman and Boggs, 2004) or with the help of message passing interface (MPI) running on PC-clusters (Mackie et al, 2001). Newman et al (2003) described an excellent application of this approach to the synthetic and experimental 3-D radio MT dataset (N = 25600, M = 132553; N NLCG = 68; t cpu = 120 h using 252 processors on the Sandia Nat.…”

Section: How Is It Commonly Solved?mentioning

confidence: 99%

“…For synthetic examples considered in the paper of Newman and Commer (2005) they found that the migration of the initial data error into the model as presented by Zhdanov and Portniaguine (1997), without iteration or preconditioning, is not an effective imaging strategy. Mackie et al (2001) also implemented the NLCG approach to solve the 3-D MT inverse problem (typical example, N = 2000, M=39 Â 44 Â 19 = 32604; N NLCG = 20; t cpu = 10-12 h on a 400 MHz desktop computer). These authors are able to invert wideband (1000-0.001 Hz) MT datasets with up to 600 MT sites and with model grids up to 70 Â 70 Â 40.…”

Section: How Is It Commonly Solved?mentioning

confidence: 99%

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Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

Avdeev

2005

Surv Geophys

238

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The whole subject of three-dimensional (3-D) electromagnetic (EM) modelling and inversion has experienced a tremendous progress in the last decade. Accordingly there is an increased need for reviewing the recent, and not so recent, achievements in the field. In the first part of this review paper I consider the finite-difference, finite-element and integral equation approaches that are presently applied for the rigorous numerical solution of fully 3-D EM forward problems. I mention the merits and drawbacks of these approaches, and focus on the most essential aspects of numerical implementations, such as preconditioning and solving the resulting systems of linear equations. I refer to some of the most advanced, state-of-the-art, solvers that are today available for such important geophysical applications as induction logging, airborne and controlled-source EM, magnetotellurics, and global induction studies. Then, in the second part of the paper, I review some of the methods that are commonly used to solve 3-D EM inverse problems and analyse current implementations of the methods available. In particular, I also address the important aspects of nonlinear Newton-type optimisation techniques and computation of gradients and sensitivities associated with these problems.

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Section: How Is It Commonly Solved?mentioning

confidence: 99%

Section: How Is It Commonly Solved?mentioning

confidence: 99%

Section: How Is It Commonly Solved?mentioning

confidence: 99%

Section: How Is It Commonly Solved?mentioning

confidence: 99%

See 2 more Smart Citations

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

Avdeev

2005

Surv Geophys

238

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“…It is also planned to apply our inversion scheme to an experimental data set. However, previous examples from other 3-D MT inversion software developers (see [8,10,14,17]) indicate that successful verification of the inversion technique even on a single practical dataset is a complex task and may take some time.…”

Section: Resultsmentioning

confidence: 99%

A Rigorous Three-Dimensional Magnetotelluric Inversion

Avdeev¹,

Avdeeva²

2006

PIER

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Abstract-The limited-memory quasi-Newton optimization method with simple bounds has been applied to develop a novel fully threedimensional (3-D) magnetotelluric (MT) inversion technique. This nonlinear inversion is based on iterative minimization of a classical Tikhonov-type regularized penalty functional. But instead of the usual model space of log resistivities, the approach iterates in a model space with simple bounds imposed on the conductivities of the 3-D target. The method requires storage that is proportional to n cp ×N , where the N is the number of conductivities to be recovered and n cp is the number of the correction pairs (practically, only a few). This is much less than requirements imposed by other Newton type methods (that usually require storage proportional to N ×M , or N ×N , where M is the number of data to be inverted). Using an adjoint method to calculate the gradients of the misfit drastically accelerates the inversion. The inversion also involves all four entries of the MT impedance matrix. The integral equation forward modelling code x3d by Avdeev et al. [1,2] is employed as an engine for this inversion. Convergence, performance and accuracy of the inversion are demonstrated on a 3D MT synthetic, but realistic, example.

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Electrical conductivity of the Pampean shallow subduction region of Argentina near 33 S: Evidence for a slab window

Burd

Booker

Mackie³

et al. 2013

Geochem Geophys Geosyst

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[1] We present a three-dimensional (3-D) interpretation of 117 long period (20-4096 s) magnetotelluric (MT) sites between 31 S and 35 S in western Argentina. They cover the most horizontal part of the Pampean shallow angle subduction of the Nazca Plate and extend south into the more steeply dipping region. Sixty-two 3-D inversions using various smoothing parameters and data misfit goals were done with a nonlinear conjugate gradient (NLCG) algorithm. A dominant feature of the mantle structure east of the horizontal slab is a conductive plume rising from near the top of the mantle transition zone at 410 km to the probable base of the lithosphere at 100 km depth. The subducted slab is known to descend to 190 km just west of the plume, but the Wadati-Benioff zone cannot be traced deeper. If the slab is extrapolated downdip it slices through the plume at 250 km depth. Removal of portions of the plume or blocking vertical current flow at 250 km depth significantly changes the predicted responses. This argues that the plume is not an artifact and that it is continuous. The simplest explanation is that there is a ''wedge''-shaped slab window that has torn laterally and opens down to the east with its apex at the plume location. Stress within the slab and seismic tomography support this shape. Its northern edge likely explains why there is no deep seismicity south of 29 S.

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3‐D magnetotelluric inversion for resource exploration

Cited by 30 publications

References 6 publications

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

Three-Dimensional Electromagnetic Modelling and Inversion from Theory to Application

A Rigorous Three-Dimensional Magnetotelluric Inversion

Electrical conductivity of the Pampean shallow subduction region of Argentina near 33 S: Evidence for a slab window

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