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00925njm 22002777a 4500 dc Miensopust, Marion P. author Queralt i Capdevila, Pilar author Jones, Alan G. author Avdeev, Dmitry author Avdeeva, Anna author Börner, Ralph-Uwe author Bosch Ros, David author Egbert, Gary author Farquharson, Colin author Franke-Bönner, Antje author Garcia, Xavier author Han, Nuree author Hautot, Sophie author Holtham, Elliot author Hübert, Juliane author Khoza, David author Kiyan, Duygu author Le Pape, Florian author Ledo Fernández, Juanjo author Lee, Tae Jong author Mackie, Randall author Martí i Castells, Anna author Meqbel, Naser author Newman, Greg author Oldenburg, Doug author Rosell Novel, Oriol author Sasaki, Yutaka author Siripunvaraporn, Weerachai author Tarits, Pascal author Vozar, Jan author 2020-05-21T07:25:29Z 2020-05-21T07:25:29Z 2013 2020-05-21T07:25:30Z Over the last half decade the need for, and importance of, three-dimensional (3-D) modelling of magnetotelluric (MT) data have increased dramatically and various 3-D forward and inversion codes are in use and some have become commonly available. Comparison of forward responses and inversion results is an important step for code testing and validation prior to 'production' use. The various codes use different mathematical approximations to the problem (finite differences, finite elements or integral equations), various orientations of the coordinate system, different sign conventions for the time dependence and various inversion strategies. Additionally, the obtained results are dependent on data analysis, selection and correction as well as on the chosen mesh, inversion parameters and regularization adopted, and therefore, a careful and knowledge-based use of the codes is essential. In 2008 and 2011, during two workshops at the Dublin Institute for Advanced Studies over 40 people from academia (scientists and students) and industry from around the world met to discuss 3-D MT inversion. These workshops brought together a mix of code writers as well as code users to assess the current status of 3-D modelling, to compare the results of different codes, and to discuss and think about future improvements and new aims in 3-D modelling. To test the numerical forward solutions, two 3-D models were designed to compare the responses obtained by different codes and/or users. Furthermore, inversion results of these two data sets and two additional data sets obtained from unknown models (secret models) were also compared. In this manuscript the test models and data sets are described (supplementary files are available) and comparisons of the results are shown. Details regarding the used data, forward and inversion parameters as well as computational power are summarized for each case, and the main discussion points of the workshops are reviewed. In general, the responses obtained from the various forward models are comfortingly very similar, and discrepancies are mainly related to the adopted mesh. For the inversions, the results show how the inversion outcome is affected by distortion and the choice of errors, as well as by the completeness of the data set. We hope that these compilations will become useful not only for those that were involved in the workshops, but for the entire MT community and also the broader geoscience community who may be interested in the resolution offered by MT. Geomagnetisme Prospecció magnetotel·lúrica Prospecció geofísica Geomagnetism Magnetotelluric prospecting Geophysical exploration Magnetotelluric 3D inversion - a recapitulation of two successful workshop on forward and inversion code testing and comparison