TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 54 (No. 5), pp. 499-509, 2002

A new computation method for a staggered grid of 3D EM field conservative modeling

Elena Yu. Fomenko1 and Toru Mogi2

1Geoelectromagnetic Research Institute RAS, Troitsk, Moscow Region 142092, Russia
2Institute of Seismology and Volcanology, Hokkaido University, Sapporo 060-0810, Japan

(Received January 9, 2001; Revised August 8, 2001; Accepted September 21, 2001)

Abstract: A new three-dimensional (3D) MT modeling scheme conserving electric current and magnetic flux is developed. The scheme is based on finite difference (FD) staggered rectangular non-uniform grid formulation for the secondary electric field with continuous components of tangential electric and normal magnetic fields, in contrast to existing FD algorithms with a discontinuous E-field at the face of the cells. The scheme leads to a sparse 13-band complex symmetrical system of linear equations, which is effectively solved by fast and stable conjugate gradient (CG) methods. The preconditioning procedure was used to decrease the condition of a number of an ill-conditioned matrix system by several orders and stably and quickly solves the matrix system. The special module for the correction of divergence-free current J greatly increased the speed of convergence and accuracy, especially at low frequencies and for high-contrast resistivity or conductivity structures. A special procedure was developed to improve the accuracy of tangential magnetic and vertical electrical components at the Earth's surface and at the interface with a large conductivity contrast. The validity of the new algorithm was demonstrated for difficult models with high-contrast resistivity structures including topography and for COMMEMI project models.

Corresponding author E-mail: efomenko@cs.msu.su

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