3D inversion of time-domain electromagnetic data using finite elements and a triple mesh formulation

• DOI: 10.1190/geo2020-0079.1
• Publication Date: 2021-03-11T00:48:06Z
• Authors: Bo Zhang; Kim Wann Engebretsen; Gianluca Fiandaca; Hongzhu Cai; Esben Auken
• Keywords: 3-D INVERSION; TOPOGRAPHY; SOLVER; 3-DIMENSIONAL MAGNETOTELLURIC INVERSION; 01 natural sciences; 0105 earth and related environmental sciences

Over several decades, much research has been done to develop 3D electromagnetic inversion algorithms. Due the computational complexity and memory requirements for time-domain (TEM) algorithms, many real-world surveys are inverted within one dimension. To speed up calculations manage inversions of TEM data, we have developed an approach using three uncoupled meshes: mesh, a forward-model mesh Jacobian calculations. The is coarse regular structured such that constraints easily enforced between model parameters. Forward responses calculated on dense unstructured obtain accurate fields, whereas mesh. We found sufficient converge and, equally important, it provides significant boost in overall process, compared calculating forward-modeling meshes made tetrahedral elements, fields finite-element method. optimization uses standard Gauss-Newton formulation. For further optimizing inversion, use domain decomposition each transmitter separately parallelize problem over domains OpenMP. Compared 1D solution, accuracy 1%–5% 2%–7% but calculation time approximately five times faster also examined algorithm small ground-based data set acquired area where earth distorts degree not feasible.