Improved workflow for 3D inverse modeling of magnetotelluric data: Examples from five geothermal systems

• Standard approach to 3D MT finite difference inversion can be inefficient and yield poor solutions.
• Alternative sequenced 3D MT finite difference workflow is proposed.
• Sequenced workflow retrieves better-fitting 3D solutions at lower cost.
• Examples from five geothermal fields.

Magnetotellurics (MT) is now an important geophysical tool for imaging complex geothermal energy systems, but retrieving realistic three-dimensional (3D) resistivity models is challenging, and computationally intensive. To ameliorate this situation, we develop a sequenced MT inversion workflow that formalizes and improves upon concepts introduced by Rosenkjaer and Oldenberg (2012). We test the performance and reliability of our workflow using five 3D MT datasets from geothermal fields in the United States (Coso, Raft River) and Iceland (Krafla, Hengill and Krysuvik). We compare inversion results from the standard and sequenced workflows for each experiment, and find that the sequenced workflow always retrieves a better-fitting model, specifically at lower frequencies, which is geologically consistent and representative of a high temperature geothermal system. It also uses fewer computational resources.