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In many cases, the lateral extension of economically valuable mineral deposits is linked to fractures. Knowing the characteristics of these tectonic structures is crucial for determining the continuity of mineralization in the subsoil and, consequently, for planning their exploitation. To address this challenge, a multidisciplinary study was carried out using various geophysical techniques and direct field observations to analyze the effectiveness of each technique in the investigation of fractures. For this purpose, the mining district of Linares-La Carolina in southeastern Spain, known for hosting Philonian deposits of galena (PbS), was chosen. At the southern boundary of this mining district, the seams stopped being exploited when they lost their continuity due to the presence of a regional normal fault. This fault zone was responsible for hiding the seams under a thick sedimentary cover. Detailed geological mapping allowed us to deduce the presence of two fracture systems. The geophysical techniques of electrical resistivity tomography and the time domain electromagnetic method were used, allowing us to identify the positions and the vertical displacement of these faults. Furthermore, using magnetometry, the presence of a third system of fractures was deduced. The results showed that this multidisciplinary analysis provides information of interest concerning the complex structure that configures the limits of this mining district. [ABSTRACT FROM AUTHOR]

In many cases, the lateral extension of economically valuable mineral deposits is linked to fractures. Knowing the characteristics of these tectonic structures is crucial for determining the continuity of mineralization in the subsoil and, consequently, for planning their exploitation. To address this challenge, a multidisciplinary study was carried out using various geophysical techniques and direct field observations to analyze the effectiveness of each technique in the investigation of fractures. For this purpose, the mining district of Linares-La Carolina in southeastern Spain, known for hosting Philonian deposits of galena (PbS), was chosen. At the southern boundary of this mining district, the seams stopped being exploited when they lost their continuity due to the presence of a regional normal fault. This fault zone was responsible for hiding the seams under a thick sedimentary cover. Detailed geological mapping allowed us to deduce the presence of two fracture systems. The geophysical techniques of electrical resistivity tomography and the time domain electromagnetic method were used, allowing us to identify the positions and the vertical displacement of these faults. Furthermore, using magnetometry, the presence of a third system of fractures was deduced. The results showed that this multidisciplinary analysis provides information of interest concerning the complex structure that configures the limits of this mining district.

In order to increase the geothermal exploration, the magnetotelluric (MT) method has been used to study the subsurface of the Seulawah Agam volcano, Aceh Province, Indonesia. Similar to all resistivity methods that are based on measuring the electric field on the surface, the MT commonly contains a static shift problem, which is caused by the heterogeneities near the surface and the different topography of the volcano. The static effect can be expressed as a vertical shift from the apparent resistivity curve. In this study, the apparent resistivity data from the 1D inversion of the Transient Electromagnetic (TEM) method were used to correct the static shift problem in the MT data. Both methods were acquired in the same site at ten stations along with a 12 km distance profile that crosses the Seulawah Agam volcano. The north-south profile of the volcano area appeared to host a geothermal system. The 1D inversion in the TEM data shows a low resistivity layer that indicated a cap rock with a thickness up to 1000 m. The area below the cap rock is estimated to be a reservoir zone while the 2D inversion of MT shows that the deep conductor below 2000 m could be the heat source for the Seulawah Agam geothermal system. [ABSTRACT FROM AUTHOR]

Fifty transient electromagnetic (TEM) and 15 audio-magnetotelluric (AMT) soundings were carried out in the west central part of Portugal over an area of approximately 40 km2 to characterize the geological formations associated with the Monte Real aquifer in order to (1) assess the spatial extent of the aquifer, (2) detect the zones of higher water productivity and (3) evaluate the aquifer salinization risk. The dimensionality and strike direction of the AMT profiles were studied using phase tensor analysis and the AMT data was inverted using a two-dimensional (2D) nonlinear conjugate-gradient algorithm. In addition, the TEM soundings were inverted using a one-dimensional (1D) Levenberg-Marquardt technique in order to obtain 1D layered-earth resistivity models. The TEM results reveal that the aquifer is not uniform in the study area; a more resistive zone is evident in the north and northeast of the investigated area where we expect to have higher productivity. On the other hand, the AMT models suggest that the aquifer basement is probably located at a depth of more than 800 m. Based on the results of this investigation, no traces of saltwater intrusion were found for the Monte Real aquifer. Therefore, we assume that the risk of saltwater intrusion is small in the study area. [ABSTRACT FROM AUTHOR]

The Pian Grande di Castelluccio (PGC) basin is the main Quaternary depocenter of the Mt. Vettore‐Mt. Bove normal fault system (VBFS), responsible for the 30 October 2016 Mw 6.5 Norcia earthquake (central Italy). Coseismic surface faulting through the basin attests the occurrence of active splays of the seismogenic master fault; thus, we explore the subsurface basin structure to infer the long‐term behavior of the VBFS. We integrate electrical resistivity tomography (ERT), time domain electromagnetic soundings (TDEM), and horizontal‐to‐vertical spectral ratios of ambient seismic vibrations (HVSR) along a transect crossing the surface ruptures. The ERT models provide high‐resolution details of three shallow fault zones. One‐dimensional resistivity models from TDEM and HVSR frequency peaks suggest abrupt steps in the top bedrock caused by previously unknown faults and indicate an infill thickness of up to ~300 m. We also analyze shear wave splitting of S phases (fast direction φ and delay time δt) from local earthquakes recorded during our surveys to better constrain the fracture field and the properties of the inferred fault zones. We relate the retrieved pattern of fault‐parallel φ, and the associated larger δt, to the main and secondary faults in the upper crust and to the cracks or shear fabric in the damage zones of the active splays. The PGC basin is due to the interference of an older N30° striking fault system subsequently crosscut by the N150° striking VBFS, which is currently active, seismogenic, and capable of rupturing the surface during M > 6 earthquakes. Key Points: We explore the subsurface of the Pian Grande di Castelluccio basin, across the 30 October 2016 Mw 6.5 central Italy earthquake faultElectrical resistivity models, ambient noise, and seismic anisotropy analyses constrain the basin geometry and the faults patternThe complex subsurface setting is caused by two fault systems with different timing of activity that created ~300‐m‐deep depocenters [ABSTRACT FROM AUTHOR]