An accelerated solution strategy for 3D multi-frequency controlled source electromagnetic modeling using a hybrid direct-iterative solver

Abstract An efficient modeling engine is essential for interpretation of frequency domain controlled source electromagnetic (CSEM) data. In practical surveys, CSEM fields from multiple frequencies are usually excited to enhance spatial resolution in complex geologic environment. In this study, we present an effective solution strategy for 3D CSEM simulations when a large number of frequencies is involved. Computational efficiency is achieved by utilizing a hybrid direct-iterative solver, where the CSEM simulation at one selected frequency is first solved by a direct solver, and the resulting LU decomposition is then used as an effective preconditioner for iterative solving of the CSEM forward problems at other frequencies of interest. A rule of thumb for the selection of the LU preconditioner is proposed when multiple frequencies are simulated for a given model. We investigate the reusability of the LU preconditioner when the conductivity structures of the model are perturbed. The results demonstrate the effectiveness of the reuse of the LU preconditioner, which offers computational benefits for CSEM inversion and resolution analysis, where a large number of simulations with perturbed models is required.