FEMTIC (Finite Element MagnetoTelluric Inversion Code)
FEMTIC is a 3-D magnetotelluric inversion code based on the following studies.
Y. Usui, 3-D inversion of magnetotelluric data using unstructured tetrahedral elements: applicability to data affected by topography, Geophys. J. Int., 202 (2): 828-849, doi.org/10.1093/gji/ggv186, 2015.
Y. Usui, Y. Ogawa, K. Aizawa, W. Kanda, T. Hashimoto, T. Koyama, Y. Yamaya and T. Kagiyama, Three-dimensional resistivity structure of Asama Volcano revealed by data-space magnetotelluric inversion using unstructured tetrahedral elements, Geophys. J. Int., 208 (3): 1359-1372, doi.org/10.1093/gji/ggw459, 2017.
Y. Usui, T. Kasaya, Y. Ogawa and H. Iwamoto, Marine magnetotelluric inversion with an unstructured tetrahedral mesh, Geophys. J. Int., 214(2): 952-974, doi.org/10.1093/gji/ggy171, 2018.
Y. Usui, M. Uyeshima, H. Hase, H. Ichihara, K. Aizawa, T. Koyama, et al. 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, 2024
FEMTIC was made using object-oriented programming with C++.
FEMTIC enables us to incorporate topography and bathymetry into an inversion model.
FEMTIC is applicable to land magnetotelluric survey data as well as ocean bottom magnetotelluric survey data.
Functional overview
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
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
GitHub repository
Source codes, manuals, and sample input files of FEMTIC can be downloaded from the following GitHub repository.
Release note
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.
Pre/post-processing tools for FEMTIC
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
Sample input files of meshing tools can be downloaded from the web folder below.
drive.google.com/drive/folders/1eQsbADsvHQ3EvEQshbZhG9Pv57NLivkM?usp=sharing
Studies using FEMTIC
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
Mesh for modeling around Amami Oshima island, Japan
Mesh for modeling around Asama volcano, Japan
Non-conforming deformed hexahedral mesh representing Izu Oshima Island, Japan