FEMTIC gives a three-dimensional electrical resistivity structure from the response functions at observation points on the Earth's surface. 

• Mesh type: Tetrahedral mesh / Hexahedral brick mesh / Non-conforming deformed hexahedral mesh

• Data type: Impedance tensor / Vertical magnetic transfer function / Inter-station horizontal magnetic transfer function / Phase tensor / Apparent resistivity & Phase / Network-MT response function / Impedance tensor obtained from the Network-MT response functions / Apparent resistivity & Phase obtained from the Network-MT response functions 

• Inversion algorithm: Model-space Gauss-Newton method / Data-space Gauss-Newton method

• Parallel computation: Multiple processes parallel computation with MPI / Multiple threads parallel computation with OpenMP / MPI & OpenMP hybrid parallel computation

• Model parameter: Subsurface electrical resistivity / Distortion matrix of galvanic distortion

• Regularization: L2 regularization with Laplacian filter / L2 regularization with difference filter /  L1 regularization with difference filter

Source codes, manuals, and sample input files of FEMTIC can be downloaded from the following GitHub repository.

github.com/yoshiya-usui/femtic.git 

v4.3 Feb. 6, 2025: The directory for the out-of-core files of the sensitivity matrix becomes changeable. 

v4.2 Mar. 25, 2024: I modified some parts to allow the use of large-scale models and large datasets.

v4.1 Nov. 9, 2021: This new version supports difference filter. The error calculation of log10(apparent resistivity) is modified. Rotation angles of distortion matrix are limited to from -90 to 90 (deg.) when gains and rotations of galvanic distortion are estimated.

v4.0 Jun. 3, 2021: This new version supports non-conforming deformed hexahedral mesh.

v3.5 Jan. 11, 2021: This new version supports observed data of apparent resistivity and phase and unsymmetric roughening matrix.

v3.4.7 Sep. 4, 2020: The integer indices into the multiple right-hand-side vectors and solution vectors were changed from 32-bit to 64-bit.

v3.4.6 Sep. 2, 2020: This version allows us to make resistivity of every individual subsurface element to be a different model parameter, in analogy with other 3-D inversion code.

Some pre/post-processing tools for FEMTIC, including meshing tools, and their manuals can be downloaded from GitHub. Results of FEMTIC can be visualized by ParaView.

makeDHexaMesh :  Tool for making non-conforming deformed hexahedral mesh for FEMTIC

makeTetraMesh : By using this tool, you can make a surface mesh for creating a tetrahedral mesh.

makeMtr : This tool output .mtr file of TetGen by reading node and .ele files of TetGen.

TetGen2Femtic : This program converts output files of TetGen to FEMTIC.

makeHexaMesh : Tool for making hexahedral brick mesh for FEMTIC

mergeResultOfFEMTIC : By this program, you can merge result files (.csv) of FEMTIC.

makeCutawayForGMT : By using this program, you can make a file needed to draw a cross-section of a resistivity structure by GMT.

changeResistivityForFemtic : By this program, you can change resistivity values of a specified area for sensitivity tests of FEMTIC inversion results

Sample input files of meshing tools can be downloaded from the web folder below.

drive.google.com/drive/folders/1eQsbADsvHQ3EvEQshbZhG9Pv57NLivkM?usp=sharing 

• Uchida, T., & Yamaya, Y. (2025). Reliability of 3D finite-element and finite-difference inversion of magnetotelluric data including topography for geothermal exploration: Case study in Okuaizu geothermal field. Geothermics, 127, 103213. doi.org/10.1016/j.geothermics.2024.103213 

• W. Heise, S. Bannister, C. A. Williams, P. McGavin, T. G. Caldwell, E. A. Bertrand, Y. Usui, G. Kilgour, Magmatic priming of a phreatic eruption sequence: The 2012 Te Maari eruptions at Mt Tongariro (New Zealand) imaged by Magnetotellurics and Seismicity, Geophys. J. Int., https://doi.org/10.1093/gji/ggae022, 2024.

• 内田利弘; 山谷祐介. 有限要素法および差分法による MT 法データの 3 次元解析: 八甲田北部地域への適用. 日本地熱学会誌, 45.3, https://doi.org/10.11367/grsj.45.175, 2023.

• D. Diba, M. Uyeshima, M. Ichiki, S. Sakanaka, M. Tamura, Y. Yuan, M. Gresse, Y. Yamaya and Y. Usui,  On a large magmatic fluid reservoir oblique to the volcanic front in the southern part of NE Japan revealed by the magnetotelluric survey, Earth Planets Space, 75:146, https://doi.org/10.1186/s40623-023-01899-0, 2023.

• A. Honda, W. Kanda, T. Koyama et al. Shallow resistivity structure around the 2018 craters of Mt. Motoshirane of Kusatsu-Shirane Volcano, Japan, revealed by audio-frequency magnetotellurics. Earth Planets Space, 75, 43. https://doi.org/10.1186/s40623-023-01799-3, 2023

• K., Seki, W., Kanda, K., Mannen, S., Takakura, T., Koyama, R., Noguchi, et al. Imaging the source region of the 2015 phreatic eruption at Owakudani, Hakone Volcano, Japan, using high‐density audio‐frequency magnetotellurics. Geophysical Research Letters, 48, e2020GL091568. https://doi.org/10.1029/2020GL091568, 2021

• K. H. Tseng, Y. Ogawa, Nurhasan, S. B. Tank, N. Ujihara, Y. Honkura, A. Terada, Y. Usui and W. Kanda, Anatomy of active volcanic edifce at the Kusatsu–Shirane volcano, Japan, by magnetotellurics: hydrothermal implications for volcanic unrests, Earth Planets Space, 72:161, doi.org/10.1186/s40623-020-01283-2, 2020.

• W. Kanda, M. Utsugi, S. Takakura, and H. Inoue, Hydrothermal system of the active crater of Aso volcano (Japan) inferred from a three-dimensional resistivity structure model, Earth Planets Space, 71:37, https://doi.org/10.1186/s40623-019-1017-7, 2019.

• R. Yoshimura, Y. Ogawa, Y. Yukutake, W. Kanda, S. Komori, H. Hase, T. Goto, R. Honda, M. Harada, T. Yamazaki, M. Kamo, S. Kawasaki, T. Higa, T. Suzuki, Y. Yasuda, M. Tani and Y. Usui, Resistivity characterisation of Hakone volcano, Central Japan, by three-dimensional magnetotelluric inversion, Earth Planets Space, 70:66, doi.org/10.1186/s40623-018-0848-y, 2018.

• Usui, Y., Uyeshima, M., Hase, H., Ichihara, H., Aizawa, K., Koyama, T., et al. (2024). Three-dimensional electrical resistivity structure beneath a strain concentration area in the back-arc side of the northeastern Japan arc. Journal of Geophysical Research: Solid Earth, 129, e2023JB028522. http://doi.org/10.1029/2023JB028522