Magnetotelluric data were collected in the late 1990s in the Central Andes of Chile and Bolivia, with the aim to delineate the electrical conductivity distribution in the subsurface and its relations to subduction processes. In previous studies, these data were interpreted based on 2-D models. The principal result was a vast conductivity zone beneath the Altiplano high plateau at mid and lower crustal depths and a much smaller, though significant conductor associated with the Precordillera Fault System. However, there are some significant 3-D effects in the investigation area, in particular near the coast and on the eastern Altiplano. The aim of this work is to give a reinterpretation based on new 3-D inversion of these data. The 3-D inversion not only provides a better fit to the data compared to 2-D results but furthermore allows to include sites with strong telluric distortion which were ignored in previous studies. We are now able to explain anomalous phases above 90° and induction arrows pointing subparallel to the coast as observed at several sites in the Coastal Cordillera. These strongly distorted data are caused by highly conductive near-surface structures that are partly connected to the Pacific Ocean, forcing currents to flow around the sites. The lower crust beneath the Coastal Cordillera resembles a poorly conductive, nearly homogeneous half-space and is electrically unremarkable. Besides, we can now image the Precordillera conductor as a continuous, elongated feature. The volcanic arc of the Western Cordillera is highly resistive with the exception of a few conductive spots which may be associated with certain individual volcanoes or geothermal resources, respectively. The Altiplano conductor is again the dominant electrical feature in the Central Andes, indicating widespread melting of the middle and lower back-arc crust.

The North German Conductivity Anomaly was detected already in the early years of electromagnetic deep sounding. It refers to the reversal of induction arrows (as a graphical representation of the tipper transfer function, the ratio of vertical to horizontal magnetic field variations) at the northern and southern margins of the North German Basin. In spite of the many experiments carried out so far, its origin has remained ambiguous; explanations encompass a deep-crustal or even mantle source as well as the simple response to deepening of sedimentary sequences in the centre of the basin. Here, we report on modelling of new long-period magnetotelluric data collected along two profiles in NE Germany and S Sweden, with one transect crossing the Sorgenfrei–Tornquist Zone as the main boundary between Precambrian Baltica and the Palaeozoic belts of central Europe. With the exception of a few sites probably influenced by 3-D salt domes, the data allow a 2-D analysis. Resolution is reduced for large depths due to a well-conducting, saline aquifer, extending across the entire basin. The main result is that the reversal of induction arrows can largely be explained by the resistivity contrast between crystalline basement and sedimentary basin fill. Beneath Rügen island, a southward dipping conductor is interpreted to reflect an alum shale layer in Middle Cambrian–Lower Ordovician sediments. Beneath the southern basin, a moderately conductive upper mantle is modelled (although not very well resolved) which may reflect the thinning of the lithosphere as implied by seismic tomography. As the main anomalously inductive effect is primarily explained by the basin edges and numerous other anomalies exist inside the basin, we suggest not using the term ‘North German Conductivity Anomaly’ any longer.

The Trans‐European Suture Zone (TESZ) is the largest tectonic boundary in Europe, crossing northwest‐southeast through central Europe from the North Sea to the Black Sea. More than 2000 kilometers long, it constitutes a complex transition between the thick and cold East European Craton (EEQ/Baltic Shield, created more than 650 million years ago (Ma) during the Precambrian, and the warmer, younger Paleozoic (650 to 250 Ma) central European mobile belts.

The geoelectric properties of the geothermal system associated with the Tolhuaca volcano were investigated by three-dimensional (3D) inversion of magnetotelluric (MT) data. This study presents the first resistivity model of the Tolhuaca volcano derived from 3D MT inversion to have a better understanding of its magmatic and hydrothermal system. We selected data from 54 MT stations for 3D inversion. We performed a series of 3D MT inversion tests by changing the type of data to be inverted, as well as the starting model to obtain a model in agreement with the geology. The final 3D MT model presents a conductive body (<20 Ωm) located 2 km below the summit of Tolhuaca volcano, inferred as a shallow magmatic storage compartment. We also distinguish a ~300 m thick layer of high conductivity (1800 m from the surface) that had so far not been identified by previous resistivity models. The result of this study provides new insights into the complexity of the Tolhuaca geothermal system.