Improved Integral Equation Method for Rapid 3-D Forward Modeling of Magnetotelluric

Computational cost tremendously restricts the wide application of conventional integral equation (IE) method in large-scale magnetotelluric (MT) modeling. A couple obstacles limit developments traditional MT modeling based on IE method. They are: O (N2) space complexity memory requirements for storing coefficients dense matrix; singularity Dyadic Green’s function; low efficiency using digital filtering, such as Hankel transform, to calculate Bessel function within dyadic function, well inefficiency accumulative calculation 3-D discrete convolution. To solve these problems, we use an analytical formula instead transform compute and replace a block cell by spherical with same volume integrate through singularity. Because coefficient matrices are symmetric antisymmetric three-level block-Toeplitz (BT) Toeplitz + matrices, only non-redundant entities matrix computed stored. Afterwards, fast Fourier (FFT) is used expedite matrix–vector multiplication at each successive iteration when contraction iterative system equations, which decreases time consumption sharply compared