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We report the experimental investigation of quasi-one-dimensional (quasi-1D) Ta2PdSe6 single crystals by magnetotransport measurements under high magnetic fields up to 31 T. The crystals show large unsaturated magnetoresistance up to (1.8 × 105%) under 31 T at 1.6 K, accompanied by remarkable resistivity oscillations. The analysis of quantum oscillations reveals the existence of five Fermi pockets, consistent with theoretical calculations. Furthermore, our investigation suggested that band structure is modified by the electron correlations in Ta2PdSe6, which may provide a platform for exploring the interplay between electron effects and topological properties in quasi-1D materials. [ABSTRACT FROM AUTHOR]

The Greater Xing'an Range (GXAR), situated in the eastern segment of the Central Asian Orogenic Belt, is a prominent orogenic belt that offers an ideal opportunity to explore the dynamic processes underlying lithospheric growth and delamination. A two‐dimensional resistivity model was obtained based on a magnetotelluric survey with 110 stations. The results identified a lateral conductor, associated with the asthenosphere, in the overall high‐resistivity lithosphere of the GXAR. This conductor was recognized as the residual trace of the asthenospheric materials upwelling along the reactivated Xinlin‐Xiguitu suture zone, manifested as the precipitation of metasomes/conductive phases or new lithosphere distributed along channels. The transformation of the GXAR, involving the lithospheric accretion and erosion from the interior, suggests a geodynamic process of thick lithospheric delamination. The erosion of asthenospheric materials from the interior of the lithosphere was deemed as a potential mode of the lithospheric growth and delamination of orogenic belts. The discontinuity of lithospheric thickness, the reactivation of paleo‐sutures, and the tectonic environment leading to mantle convection control the occurrence of this mode. Plain Language Summary: The Greater Xing'an Range (GXAR) is an important and complex orogenic belt in Northeast China. Utilizing the magnetotelluric data, we image a dependable electrical structure to depth of 200 km in the central GXAR, which reveals the laterally residual trace of the asthenospheric materials in the lithosphere. The asthenospheric materials had intruded into the crust‐mantle boundary through the reactivated suture zone, and triggered vertical accretion and lateral erosion of the lithosphere from its interior. It caused the growth and delamination of the GXAR lithosphere. Key Points: The lithosphere of the Greater Xing'an Range features a prominent laterally relatively conductive structureThe asthenospheric materials that intruded along the suture zone transformed the lithosphere of the orogenic beltThe erosion and accretion of asthenospheric materials from the interior of the lithosphere is a potential mode of the lithospheric growth and delamination of orogenic belt [ABSTRACT FROM AUTHOR]

The general subject of this article deals with the term salt. Salt deposits usually contain chlorides, sulphates/gypsum, borates, carbonates, etc., that are seemingly part of the same system. Even though this article mainly presents data and observations on chlorides, which are not easily explained by the present paradigm, it should also prove relevant for the formation of sulphates and other types of salts observed in major salt deposits. The paradigm explaining large salt deposits rests on two pillars governing salt formation and salt deformation. Salt formation is thought to occur vis solar evaporation of seawater in restricted basins. Salt deformation and forming of salt diapirs is thought to occur due to gravity-induced movements. Our review presents peer-reviewed and published data and observations from different authors within different disciplines that challenge the present evaporite paradigm. The current theory/paradigm rests on numerous observations and interpretations in support of it. Adding more observational interpretations in support of the paradigm will not nullify even one observation that contradicts or remains unexplained by the theory. The contradicting evidence must be explained within the present paradigm for it to survive. Significant observations of and within salt deposits are presented, as well as visual and geophysical observations of salinity in crusts and mantles in relevant tectonic settings. In our view, the omnipresent salinity observed in the subsurface needs to be understood and included in the description of a new salt formation mechanism in order to fully explain all features presented herein. [ABSTRACT FROM AUTHOR]

In this research, an arbitrarily oriented electric dipole at subsurface is used to simulate Seismogenic Electromagnetic (SEM) radiation emanating from a seismic zone during its gestation phase. Analytical synthesis of responses at the Lijiang magnetotelluric (MT) station has revealed that SEM radiation could induce identifiable anomalies in the electromagnetic (EM) spectrum, apparent resistivity and phase within specific frequency bands. Background variations were extracted from long-term observation data of Dali and Lijiang MT stations, enabling the identification of SEM anomalies related to the Yunlong and Yangbi earthquakes. Multiple parameters of dipole sources at subsurface were obtained by applying the Differential Ant Colony Optimization (DACO) algorithm to anomalous data of two stations with multi-frequencies and various response functions. The spatial distribution of these predicted dipoles is predominantly clustered in or around the seismogenic area, with their azimuthal orientation aligning towards the seismogenic fault in general. This study has demonstrated the potential of using subsurface electric dipole simulations for SEM radiation analysis, offering a feasible approach for the prediction and understanding of seismogenic zones. [ABSTRACT FROM AUTHOR]

The paleochannels in coastal areas may be the priority channels for saltwater intrusion, and identifying paleochannels is important for revealing the pollution mechanisms of coastal zone aquifers and protecting groundwater resources. The use of electrical methods to identify paleochannels has become common. Still, the highly dynamic hydrological characteristics of saltwater intrusion area and the differences in the conductive properties of saltwater and freshwater increase the uncertainty of the interpretation process. This study combined groundwater numerical simulation data, hydrochemical data and stratigraphic data to construct an electrical model of the paleochannel, which provides a reference for the interpretation of paleochannel using ERT data. The paleochannel electrical model constructed by combining multiple sources of data reflects the spatial heterogeneity of resistivity values of paleochannel in different seasons and at varying levels of saltwater intrusion, making the identification of paleochannel in saltwater intrusion areas more accurate. The results show that the paleochannel shows high resistivity anomalies relative to the background stratigraphy in brackish water areas, and low resistivity anomalies relative to the background stratigraphy in freshwater areas. Combining the paleochannel forward model with ERT data can effectively identify the paleochannel in saltwater intrusion areas. [ABSTRACT FROM AUTHOR]

[Display omitted] • We use magnetotellurics to image a post-subduction Porphyry mineral system. • Ore bearing mineralisation may be linked to an enriched subcontinental lithospheric mantle. • Evaluation of mineral deposits are spatially associated with zones of low resistivity. Porphyry mineral systems provide a significant source of critical minerals for modern society, that are predominantly formed in subduction related settings from magmatic hydrothermal fluids derived from an underlying reservoir. However, in post-subduction settings the processes that entrain and focus magmatic hydrothermal fluids throughout the crust, from source to deposit are often poorly constrained. In this paper, we have undertaken a magnetotelluric (MT) survey in an intracontinental tectonic setting across the Adelaide Superbasin, which is a Neoproterozoic passive margin formed during rifting of the supercontinent Rodinia. This region contains the Burra magmatic copper deposit, along with numerous sedimentary-hosted copper deposits. Systematic three-dimensional modelling was undertaken, initially at regional-scale, with 55 km gridded long-period AusLAMP data over a 500 × 500 km area, followed by infilled 10 km gridded broadband MT data, at the district-scale, centred over an area of copper deposits in the Adelaide Rift Complex. The modelling reveals an elongated zone of low electrical resistivity (∼100 Ω.m), in an otherwise resistive crust, at lower crustal depth (20–40 km) that is contiguous with the regional lineament of the Adelaide Rift Complex and copper and gold mineralisation. A narrow zone of low resistivity (∼100 Ω.m) branches through the upper crust (5–20 km) to the surface, that is remarkably aligned with the Burra magmatic mineral system, in an otherwise quite resistive crust (∼1000 Ω.m). Additionally, in the upper crust a zone of low resistivity (1–10 Ω.m at a depth of 5–8 km) extends from the Burra magmatic copper deposit southwards, constrained by anticlinal folding from the ∼500 Ma Delamerian Orogenic deformation of the Adelaide Rift Complex and spatially aligned with the Kapunda sedimentary-hosted copper deposit. We argue that the low electrical resistivity signature encapsulates a whole-of-lithosphere magmatically-hosted copper system, that is further mobilised by low-temperature fluids by mapping the footprint of ore-forming fluids from the source to associated mineralisation. Where later basin wide fluid recycling in a permeability enhanced basin, via neo-tectonism along pre-existing structures/trends, has likely remobilised copper, from a prior magmatic event, with copper being leached in chloride-rich saline fluids at low temperatures. [ABSTRACT FROM AUTHOR]

A data set consisting of 376 broadband and long‐period MT measurements was used to generate the first ever 3D resistivity model of the Archean western Superior Craton. The modeled resistivity structure is compared to coincident seismic reflection data. The observed geophysical signatures are interpreted within the context of the late stages of crustal growth and cratonization of the region via the progressive accretion of terranes against the initial cratonic core. The northern‐most terranes comprising the cratonic core exhibit a nearly homogenous highly resistive crust. The lower crust of the southern terranes contains largely continuous low resistivity bands which run subparallel to major terrane boundaries and corresponding fault systems. In some cases, low resistivity features are coincident with dense packages of sub‐horizontal to listric reflections within the mid‐ to lower crust. These resistivity structures are inferred to represent preserved geoelectric signatures of late to post‐orogenic magmatic pulses likely related to delamination of locally overthickened crust. Increased mantle heat flow resulted in partial melting of the lower crust and upper mantle and upward migration of CO2‐rich melts and fluids through crustal weak zones corresponding to shear and/or suture zones formed during terrane amalgamation. Thermal softening of the mid‐ to lower crust led to orogenic collapse and reactivation of the crustal shear zones, resulting in formation and interconnection of graphitic films which were preserved within the stable craton. These results have implications for the tectono‐magmatic history of the western Superior Craton, as well toward the understanding of the geodynamic regime of the Archean Earth. Plain Language Summary: The present day geophysical signatures of cratons, ancient continents which formed and have remained stable since the Archean roughly 2.5–4.0 billion years ago, may be used to investigate the tectonic processes that were active during their formation. Here, we combine magnetotelluric (MT) and seismic data to investigate the crust and upper‐most mantle structure of the western Superior Craton of Canada. A 3D resistivity volume of the region derived from the MT data maps electrically conductive zones within the lower crust which overlap with zones of high seismic reflectivity, and are spatially correlated with major geological terrane boundaries. These signatures are interpreted as representing electrically conductive graphite and/or sulphidic films emplaced within deep crustal shear zones as a result of crustal collapse and magmatic activity during the late stages of construction and stabilization of the Superior Craton. Our results have implications for our understanding of the processes responsible for the formation of these ancient continents. Key Points: First large‐scale 3D resistivity model of the Archean western Superior Craton reveals ∼east‐west trending low resistivity features at lower‐crustal depthsConductive features coincident with listric to sub‐horizontal seismic reflections, suggestive of mid‐ to lower crustal shear zonesPreserved geophysical signatures are indicative of late Archean tectono‐magmatic processes [ABSTRACT FROM AUTHOR]

The origin of the cosmic magnetic field remains an unsolved mystery, relying not only on specific dynamo processes but also on the seed field to be amplified. Recently, the diffuse radio emission and Faraday rotation observations reveal that there has been a microgauss-level magnetic field in intracluster medium in the early universe, which places strong constraints on the strength of the initial field and implies the underlying kinetic effects; the commonly believed Biermann battery can only provide extremely weak seed of 10-21 G. Here, we present evidence for the spontaneous Weibel-type magnetogenesis in laser-produced weakly collisional plasma with the three-dimensional synchronous proton radiography, where the distribution anisotropy directly arises from the temperature gradient, even without the commonly considered interpenetrating plasmas or shear flows. This field can achieve sufficient strength and is sensitive to Coulomb collision. Our results demonstrate the importance of kinetics in magnetogenesis in weakly collisional astrophysical scenarios. [ABSTRACT FROM AUTHOR]

The Mongol‐Okhotsk suture and the Adaatsag ophiolite belt are associated with the closure of the Mongol‐Okhotsk paleo‐ocean and are located within the Central Asian Orogenic Belt (CAOB) and Mongolia. The suture zone is flanked by volcanic‐plutonic belts that host significant metallogenic zones, containing deposits of copper and gold. The tectonic evolution of this region is not fully understood and the lithospheric structure has been poorly studied. We analyze magnetotelluric data and generate a model of the electrical resistivity distribution across this region. Whereas the northern segment has a sharp transition from a high‐resistivity upper crust to a low‐resistivity lower crust, as observed beneath the Hangai Dome, the southern segment does not show this transition. A wide, low‐resistivity zone (1–100 Ωm) imaged in the crust and lithospheric mantle is coincident with the Mongol‐Okhotsk suture and ophiolite, revealing a clear and significant lithospheric‐scale feature. Across the profile, numerous narrow, vertically oriented, low‐resistivity features (1–100 Ωm) are spatially associated remarkably well with the proposed boundaries of tectonic domains. These results confirm ideas about the development of the CAOB. Some of these low‐resistivity features are beneath the surface locations of large mineral zones, and likely represent fossil fluid pathways. We show congruent seismic velocity models for comparison and the results show a large‐scale low‐velocity anomaly (decrease of 2%–3%) that correlates with the location of the low‐resistivity anomaly below the Mongol‐Okhotsk suture. The geophysical results, combined with geological and geochemical data, provide insights into the structure of this region and help shed light on unanswered questions. Plain Language Summary: When the ancient Mongol‐Okhotsk ocean closed, due to subduction from tectonic re‐arrangement, it left the Mongol‐Okhotsk suture zone and the Adaatsag ophiolite as a trace of its location. Similarly, other tectonic boundaries are hypothesized to exist from terrane accretion across the Central Asian Orogenic Belt (CAOB) and Central and Southern Mongolia, which is located between the Siberian and North China cratons. This region is also rich in economically significant copper and gold deposits. The tectonic evolution of this region and especially the lithospheric structure is not fully understood and has been poorly studied. We analyze magnetotelluric data and generate a model of the electrical resistivity distribution. Additionally, we show models of the seismic velocity for comparison. Examining multiple complementary geophysical models helps to reduce interpretation uncertainty. Anomalies are observed in both models (e.g., low resistivity and low velocity). The suture zone is proven to be a strong lithospheric‐scale boundary. The proposed boundaries of tectonic domains are also imaged, confirming ideas about the development of the CAOB, and solving some controversies. Key Points: Lithospheric‐scale, wide, low‐resistivity zone revealed below the ophiolite belt associated with the closure of the Mongol‐Okhotsk oceanVertical, narrow low‐resistivity features aligned with proposed tectonic boundaries and locations of large mineral zones (copper and gold)The northern part of central Mongolia has a sharp mid‐crustal transition from high to low resistivity, whereas the southern part does not [ABSTRACT FROM AUTHOR]

Abstract—During the magnetotelluric studies in North Vietnam, simultaneous Phase Roll Out from Quadrant effect was detected in the behavior of impedance phases Zxy and Zyx at one of the sounding sites, CTH, in the Cam Thuy district, Thanh Hoa province. The investigation of this phenomenon has shown that it is accompanied by negative (directed upwards) components of the Umov–Poynting vector of electromagnetic energy flux in the entire range of the recorded periods of magnetotelluric variations. This energy flux direction remains unchanged when the initial coordinate system is rotated by angles of 45° and 60°. Another characteristic feature of this phenomenon is an unusual behavior of the apparent resistivity curves: the apparent resistivity magnitudes increase starting from a period of 200 s up to a period of 104 s, and this increase occurs practically along the asymptote. The analysis of the magnetotelluric field polarization and phase tensor asymmetry parameter (skew angle) β has shown that the section is characterized by significant three-dimensional (3D) distortions which manifest themselves by β values ranging between 20° and 90°. [ABSTRACT FROM AUTHOR]

Geophysical exploration of bauxite deposits has been carried out in the area of Posušje in Bosnia and Herzegovina, which were formed on an Upper Cretaceous carbonate substrate, whereas the hanging wall rocks can be Paleogene limestones and sedimentary clastic rocks. Karst terrains are demanding for geophysical exploration due to the relatively complex geological relationships and exceptional near-surface inhomogeneities that generate large noises and challenging conditions for taking field measurements. The fundamental question is whether geophysical research can detect exceptionally irregular karst bauxite deposits with relatively small dimensions. The basic idea is to combine several geophysical methods and a joint interpretation of several data sets to increase the efficiency of geophysical surveying in detecting complex bauxite deposits in karst terrains. Therefore, fundamental near-surface research methods, electrical tomography and seismic refraction are used. In addition, magnetometry was used to examine whether bauxite deposits yield potential magnetic anomalies that could help in detecting them. Research undertaken in the area of Posušje was carried out in the first step on already discovered and known bauxite deposits to determine whether geophysical responses correlate with the occurrence of bauxite deposits and to evaluate the effectiveness of each of the applied surface geophysical methods. Measurements were taken at several locations, and results for two micro-locations, Krstače and Mratnjača, are shown. Geophysical measurements were firstly performed on discovered bauxite deposits in order to reliably determine the possibility of identifying deposits in geophysical inverse models. Bauxite deposits were clearly recognised as characteristic geophysical responses in inversion models using both methods, electrical tomography and seismic refraction. Although the response of bauxite deposits is expressed in both models, resistivity and velocity, it is much more evident in resistivity models. The characteristic resistivity response was confirmed by the discovery of a new deposit. Therefore, the conclusion is that electrical resistivity tomography should be considered a basic method for exploring karst bauxite deposits. Seismic refraction provides a better characterisation of deposits and reduces the interpretation ambiguity. This solution can generally be applied to the problem of researching bauxite deposits in the Dinarides and similar geological models in the Mediterranean. Magnetometric measurements have shown that no magnetic anomalies could be associated with bauxite deposits, and only magnetometry was not successful in discovering bauxite deposits. [ABSTRACT FROM AUTHOR]

Joint inversion is a crucial approach to mitigate the non-uniqueness problem in geophysical inversion. Nevertheless, existing joint inversion methods fall short of meeting the stringent requirements of high-precision exploration, necessitating the development of new techniques. In this paper, we introduce the Structural Similarity Index (SSIM) as a novel structural consistency constraint for the joint inversion of gravity and magnetic data. Compared with the results of cross-gradient inversion, our method demonstrates outstanding performance and stability. SSIM inversion not only introduces a new class of joint inversion with structural constraints but also enhances the consistency of inversion results in the distribution of physical attribute values. The structural constraints of SSIM inversion are more comprehensive and robust, significantly improving the reliability of the inversion. Both synthetic and real data applications demonstrate that the proposed method can effectively handle both synthetic and real data, yielding outstanding results. [ABSTRACT FROM AUTHOR]

The study compares the three deep learning approaches and assesses their relative performance solving the 1-D magnetotellurics (MT) inverse problem. MT data from a 1-D geothermal-type structure are used as an example to examine Variational Autoencoder (VAE), Residual Network (Res-Net), and U-Net architectures, adapted for 1-D MT inversion. Root Mean Square Error (RMSE) and Pearson correlation coefficient are applied as misfit measure and similarity criterion, and box plot tools are used to parameterize individual model parameters. The results show that the U-Net provides the most successful recovery of the 1-D resistivity models, even though all three approaches can produce accurate inversions of MT data. To investigate applicability of results to real data sets, the models performance are examined for the case of data containing noise. Three deep learning algorithms are robust with respect to data noise, although the U-Net is relatively superior. The study results provide a platform for more complex magnetotelluric inverse problems and ones involving real data sets. [ABSTRACT FROM AUTHOR]

Outflows play a pivotal role in star formation as one of its most visible markers and a means of transporting mass, momentum, and angular momentum from the infalling gas into the surrounding molecular cloud. Their wide reach (at least thousands of astrnomical units) is a contrast to typical disk sizes (∼10–100 au). We employ high-resolution three-dimensional nested-grid nonideal magnetohydrodynamic (MHD) simulations to study outflow properties in the Class 0 phase. We find that no disk wind is driven from the extended centrifugal disk that has weak magnetic coupling. The low-velocity winds emerge instead from the infalling magnetic pseudodisk. Much of the disk actually experiences an infall of matter rather than outflowing gas. Some of the pseudodisk wind (PD-wind) moves inward to regions above the disk and either falls onto the disk or proceeds upward. The upward flow gives the impression of a disk wind above a certain height even if the gas is originally emerging from the pseudodisk. The PD-wind has the strongest flow coming from a disk interaction zone that lies just outside the disk and is an interface between the inwardly advected magnetic field of the pseudodisk and the outwardly diffusing magnetic field of the disk. The low-velocity wind exhibits the features of a flow driven by the magnetic pressure gradient force in some regions and those of a magnetocentrifugal wind in other regions. We interpret the structure and dynamics of the outflow zone in terms of the basic physics of gravity, angular momentum, magnetic fields, and nonideal MHD. [ABSTRACT FROM AUTHOR]

Western Desert region between Cairo and Fayoum in Egypt is a geologically interesting area due to its active seismicity status and the continuous bidirectional urban expansions ongoing northward and southward growth. This work aims to develop a geological model of the region by combining magnetic intensity data (aeromagnetic) and potential field data (airborne gravity) with magnetotelluric (MT) data to offer decision-makers an additional evaluation tool for long-term future planning. Applying a number of filters to aerial gravity and magnetic data allowed us to calculate the subsurface density distribution and structure of the area between Cairo and Fayoum. In addition, the surface of the crust was imaged down to a depth of 6 km using a 3-D inversion of gravity data. Magnetotelluric data were gathered at eight locations over the NS-extended Cairo-Fayoum Road profile. MT data were inverted in 2-D to generate a resistivity model that defines the subsurface structure of the researched region. The subsurface geometry in the MT-derived resistivity model agrees with the results of airborne potential measurements, and no consideration was given to any faults that may have been undetected from the potential maps. Long-term seismological observations indicated that the likely active sources of earthquakes are limited to the recognized main faults and that the ongoing "1185 buildings" construction project did not and will not cause unanticipated seismicity. The paper concludes that urban growth is secure so long as the earthquake codes are rigorously considered while planning civil projects. The northern study region must be regularly monitored for induced seismicity. On the Cairo-Fayoum Road's western side, the middle sector of the study area is the safest place for future civil developments. [ABSTRACT FROM AUTHOR]

Non-trivial spin textures driven by strong exchange interaction, magneto-crystalline anisotropy, and electron correlation in a low-dimensional magnetic material often lead to unusual electronic transitions. Through a combination of transport experiments in exfoliated nanoflakes down to 16 layers and first principle calculations, we unravel emergent electronic phases in quasi-2D van der Waals ferromagnet, Fe4GeTe2, possessing ferromagnetic TC ~ 270 K, along with a spin-reorientation transition (TSR ~ 120 K) with the change of magnetic easy axis. Two electronic transitions are identified. The first transition near TSR exhibits a sharp fall in resistivity, followed by a sign change in the ordinary Hall coefficient (R0), together with, maximum negative magnetoresistance (MR) and anomalous Hall conductivity. Another unusual electronic transition, hitherto unknown, is observed near ~ 40–50 K (TQ), where R0 again changes sign and below which, the resistivity shows a quadratic temperature dependence, and MR becomes positive. An analysis of the experimental data further uncovers the role of competing inelastic scattering processes in anomalous magnetotransport behavior. The density-functional theory based first-principle calculations unveil two possible magnetic phases, followed by a low-energy model Hamiltonian which captures the essence of these phases as well as explains the observed magnetotransport behavior. Thus, we demonstrate an interplay between magnetism and band topology and its consequence on electron transport in Fe4GeTe2, important for spintronic applications. [ABSTRACT FROM AUTHOR]

Mountains are vital water sources for humans and ecosystems, continuously replenishing lowland aquifers through surface runoff and mountain recharge. Quantifying these fluxes and their relative importance is essential for sustainable water resource management. However, our mechanistic understanding of the flow and transport processes determining the connection between the mountain block and the basin aquifer remains limited. Traditional conceptualizations assume groundwater circulation within the mountain block is predominantly shallow. This view neglects the role of deep groundwater flowpaths significantly contributing to the water, solute, and energy budgets. Overcoming these limitations requires a holistic characterization of the multiscale nature of groundwater flow along the mountain‐to‐valley continuum. As a proof‐of‐concept, we use a coupled groundwater flow and transport model to design a series of numerical experiments that explore the role of geology, topography, and weathering rates in groundwater circulation and their resulting resistivity patterns. Our results show that accumulating solutes near stagnation zones create contrasting electrical resistivity patterns that separate local, intermediate, and regional flow cells, presenting a target for magnetotelluric observations. To demonstrate the sensitivity of magnetotelluric data to features in our resistivity models, we use the MARE2DEM electromagnetic modeling code to perform forward and inverse simulations. This study highlights the potential of magnetotelluric surveys to image the resistivity structure resulting from multiscale groundwater circulation through relatively impervious crystalline basement rocks in mountainous terrains. This capability could change our understanding of the critical zone, offering a holistic perspective that includes deep groundwater circulation and its role in conveying solutes and energy. Plain Language Summary: Mountains are vital water sources for humans and ecosystems, continuously replenishing lowland aquifers through surface runoff and mountain recharge. Quantifying these fluxes and their relative importance is essential for sustainable water resource management. Here, we present a novel approach to characterize the nested nature of groundwater flow along the mountain‐to‐valley continuum by combining flow and transport models and magnetotelluric (MT) geophysical surveys. We assess the approach's potential by creating virtual realities that mimic realistic patterns of subsurface electrical resistivity. Then, using an inverse modeling approach, we test the ability of different MT survey configurations to reconstruct the resistivity fields. Our analysis shows that the accumulation of solutes in subsurface low‐velocity zones (i.e., stagnation zones) results in resistivity fields with enough contrast to image the local, intermediate, and regional groundwater flow cells. While this study is conceptual in nature, we aim to offer a framework for geophysical exploration that can characterize the critical zone without neglecting deep groundwater circulation and its role in conveying solutes and energy. Key Points: We use a coupled flow and transport model to explore the role of deep groundwater circulation in mountain‐to‐valley systemsRegional groundwater circulation conveys significant amounts of water, energy, and solutes through relatively impervious depthsMagnetotelluric surveys can potentially map the resistivity patterns created by the solute concentration patterns within the mountain block [ABSTRACT FROM AUTHOR]

Controlled-source audio frequency magnetotellurics (CSAMT) is an artificial-source electromagnetic technique that partially mitigates the limitations of weak natural-field signals. However, practical field surveys inevitably encounter strong interference, severely affecting signal quality. Traditional methods such as Fourier transformation, which directly computes apparent resistivity from frequency-domain information, are inadequate in this context, so we need alternative denoising approaches. However, research on CSAMT denoising is currently limited. Given the excellent performance of long short-term memory (LSTM) neural networks in the processing of magnetotelluric (MT) data, as demonstrated by previous studies, this paper proposes the use of LSTM to denoise CSAMT signals in the time domain. Unlike traditional denoising methods, we aim to directly extract the target frequency signal from the time-series data for denoising. For MT data, target frequency signals and noise are all mixed together, so noise suppression can only be achieved by identifying noise characteristics in the time series. However, unlike MT data, CSAMT data has an artificial transmitting source, and the frequency of the valid signal is fixed within a time interval. This allows for the direct extraction of target frequency signals without considering the complex characteristics of noise. In this study, we developed a neural network based on bidirectional LSTM to accomplish the task of noise suppression. After conducting both simulated and measured data tests, this method was able to, on average, improve the signal-to-noise ratio (SNR) of CSAMT data by approximately 20 dB and partially address the challenge of denoising when the data's SNR falls below 0 dB. [ABSTRACT FROM AUTHOR]

Geophysical data inversion typically involves the numerical solution of high-dimensional ill-posed problems. To reduce the non-uniqueness, prior information in the form of appropriate regularization schemes, together with a proper representation of the quantities of interest, is helpful. To this end, methods are recommended that take into account a low-dimensional formulation of the inverse problem, a suitable representation for the quantities of interest, and a helpful numerical procedure. Structural aspects of the objects of interest, such as the dimensions of structures, are often available as prior knowledge in archaeological magnetic surveys. However, they are not easily exploited by classical geophysical data inversion applications; for example, a typical representation together with Tikhonov-like regularization schemes or total variation, which promote smoothness in the solutions, occlude underlying structural information or retrieve fuzzy boundaries. In this work, a three-dimensional inversion of magnetic data is developed based on an evolution strategy. It is adapted to a numerical representation that easily incorporates aspects achievable at archaeological sites. Synthetic test cases and a magnetic dataset corresponding to an archaeological site are used to report the results. [ABSTRACT FROM AUTHOR]

Single‐molecule toroics are molecular magnets with vortex distribution of magnetic moments. The coupling between magnetic and electric properties such as the magnetodielectric effect will provide potential applications for them. Herein, the observation of significant magnetodielectric effect in a triangular Dy3 crystal with toroidal magnetic moment and multiple magnetic relaxations is reported. The analysis of magnetic and electric properties implies that the magnetodielectric effect is closely related to the strong spin‐lattice coupling, magnetic interactions of Dy3+ ions, as well as molecular packing models. [ABSTRACT FROM AUTHOR]

We calculate a universal shift in work function of 59.4 meV per decade of dopant concentration change that applies to all doped semiconductors and from this use Monte Carlo simulations to simulate the resulting change in secondary electron yield for doped GaAs. We then compare experimental images of doped GaAs layers from scanning electron microscopy and conductive atomic force microscopy. Kelvin probe force microscopy allows to directly measure and map local work function changes, but values measured are often smaller, typically only around half, of what theory predicts for perfectly clean surfaces. LAY DESCRIPTION: Doping means the intentional contamination of a semiconductor by foreign atoms that are integrated as ions into the crystal lattice after either donating (as donors) additional electrons or (as acceptors) electronic holes and thereby change the local electric properties. The resulting material is called n‐ or p‐doped, and pn‐junctions are used in all diodes and transistors that form the basic units of more complicated electronic devices such as computers or solar cells. We calculate how doping changes the energy needed to extract an electron from the semiconductor (called its work function) and how this influences the secondary electron yield in scanning electron microscopy and resistive or Kelvin probe measurements in conductive atomic force microscopy. Both microscopy methods can be used to directly map the spatial distribution of dopants in doped nanostructures but quantitative measurements are difficult due to the influence of surface effects. [ABSTRACT FROM AUTHOR]

Numerous studies have reported the occurrence of aseismic slip or slow slip events along faults induced by fluid injection. However, the underlying physical mechanism and its impact on induced seismicity remain unclear. In this study, we develop a numerical model that incorporates fluid injection on a fault governed by rate‐and‐state friction to simulate the coupled processes of pore‐pressure diffusion, aseismic slip, and dynamic rupture. We establish a field‐scale model to emulate the source characteristics of induced seismicity near the Dallas‐Fort Worth Airport (DFWA), Texas, where events with lower‐stress drops have been observed. Our numerical calculations reveal that the diffusion of fluid pressure modifies fault criticality and induces aseismic slip with lower stress drop values (<1 MPa), which further influence the timing and source properties of subsequent seismic ruptures. We observe that the level of pore‐pressure perturbation exhibits a positive correlation with aseismic‐stress drops but a reversed trend with seismic‐stress drops. Simulations encompassing diverse injection operations and fault frictional parameters generate a wide spectrum of slip modes, with the scaling relationship of moment (M0) with ruptured radius (r0) following an unusual trend, M0∝r04.4 ${M}_{0}\propto {r}_{0}^{4.4}$, similar to M0∝r04.7 ${M}_{0}\propto {r}_{0}^{4.7}$ observed in the DFWA sequence. Based on the consistent scaling, we hypothesize that the lower‐stress‐drop events in the DFWA may imply less dynamic ruptures in the transition from aseismic to seismic slip, located in the middle of the broad slip spectrum, as illustrated in our simulations. Plain Language Summary: Injection‐induced earthquakes have presented significant obstacles to developing energy resources related to fluid injection, such as enhanced geothermal systems and shale gas development. Despite their prevalence, the causes and impact of these earthquakes are not fully understood. Aseismic slip, characterized by slower velocities and longer durations than typical earthquakes, has been observed in induced earthquake studies. In this study, we use a numerical model to investigate how fluid pressures influence the slip properties of induced seismicity near the Dallas‐Fort Worth airport (DFWA), Texas. Our model shows that elevated fluid pressure induces aseismic slip and advances or delays fast slip (i.e., earthquakes). The pore‐pressure perturbation alters the source characteristics of both aseismic‐slip events and seismic ruptures, enhancing aseismic‐stress release while diminishing seismic‐stress release. Simulations involving various fault frictional properties reveal a wide spectrum of slip modes, ranging from slow to rapid slip, which are different from the stress‐release processes that drive globally observed natural earthquakes, but exhibit similarities to observations in the DFWA. Consequently, we infer that the DFWA events may exhibit reduced dynamic characteristics akin to slow slip events positioned in the middle of the broad spectrum generated in our modeling. Key Points: Pore‐pressure change induces aseismic slip with lower stress drops, either advancing or delaying seismic rupturesPore‐pressure perturbation exhibits a positive correlation with aseismic‐stress drops but a reversed trend with seismic‐stress dropsSimulations show a wide spectrum of induced‐slip behavior, exhibiting a similar source scaling to observations [ABSTRACT FROM AUTHOR]

Magnetotelluric data from Mount Tongariro have been analysed using an unstructured tetrahedral finite-element inversion code that incorporates topography, which was not included in previous analysis of these data. Incorporating topography adds information, which stabilizes the resistivity inversion modelling, and for the first time allows details of the shallow hydrothermal system and its relationship with the underlying magmatic system to be resolved. Specifically, an electrically conductive zone between 4 and 12.5 km depth marks the underlying magmatic system, which is shown to directly connect via conductive pathways to the area where the most recent phreatic eruptions at Tongariro occurred in 2012. The resultant phreatic eruptions in 2012 August and November showed no new magmatic component to the eruption deposits. Nevertheless, by combining the magnetotelluric resistivity image with relocated seismicity, we can see that seismicity (a proxy for magma ascent) migrated from the top of the magmatic system into the hydrothermal system in the months preceding these eruptions. Magmatic interaction with the extant hydrothermal system likely caused the over pressurization for the phreatic eruption. This work highlights the utility of combining geophysical methods and petrological data to constrain phreatic eruption processes. [ABSTRACT FROM AUTHOR]

Silicic volcanic complexes in the Main Ethiopian Rift (MER) system host long-lived shallow magma reservoirs that provide heat needed to drive geothermal systems. Some of these geothermal systems in Ethiopia appear to be suitable for green and sustainable electricity generation. One such prospect is located at the Corbetti volcanic complex near the city of Awassa. High-resolution imaging of the subsurface below Corbetti is of imminent importance, not only because of its geothermal potential, but also due to reported evidence for an ongoing magmatic intrusion. In this study, we present a new subsurface 3-D electrical conductivity model of Corbetti obtained through the inversion of 120 magnetotelluric stations. The model elucidates a magmatic system under Corbetti and reveals that it is linked to a magma ponding zone in the lower crust. Magma is transported through the crust and accumulates in a shallow reservoir in form of a magmatic mush at a depth of |$\gtrapprox 4\, {\rm km b.s.l.}$| below the caldera. The imaged extent and depth of the shallow magma reservoir is in agreement with previous geodetic and gravimetric studies that proposed an ongoing magmatic intrusion. Interpreting our model with laboratory-based conductivity models for basaltic and rhyolitic melt compositions suggests that Corbetti is seemingly in a non-eruptible state with ∼6–16 vol. per cent basaltic melt in the lower crust and ∼20–35 vol. per cent rhyolitic melt in the upper crust. With these observations, Corbetti's magmatic system shares common characteristics with volcanic complexes found in the central MER. Specifically, these volcanic complexes are transcrustal two-stage magmatic systems with magma storage in the lower and upper crust that supply heat for volcano-hosted high-temperature geothermal systems above them. According to the presented subsurface model, a cross-rift volcano-tectonic lineament exerts first-order controls on the magma emplacement and hydrothermal convection at Corbetti. Our study depicts hydrothermal convection pathways in unprecedented detail for this system and helps identify prospective regions for future geothermal exploration. 3-D imaging of both the Corbetti's magmatic and associated geothermal systems provides key information for the quantitative evaluation of Corbetti's geothermal energy potential and for the assessment of potential volcanic risks. [ABSTRACT FROM AUTHOR]

Gravity and magnetic surveys have been extensively employed in various fields like regional geology studies, environmental engineering, and mineral exploration. However, interpreting the data from these surveys remains a challenge because the potential field inversion lacks uniqueness. To address this issue, combining gravity and magnetic data in a joint inversion helps to narrow down the possible solutions. This study introduces a method for jointly inverting gravity and magnetic data, specifically focusing on the sediment–basement interface. Within this framework, a 3D voxel-type inversion using joint Gramian-based techniques incorporates a depth-to-basement model as a guiding constraint. This approach was applied to gravity and magnetic data collected around the Victoria Mine area in Nevada, USA. The joint inversion successfully produced 3D models representing the density and susceptibility of both unconsolidated sediments and the basement underlying the surveyed region. [ABSTRACT FROM AUTHOR]

Ocean bottom electromagnetic receivers (OBEMs) are invaluable tools for observing seafloor electromagnetic signals, primarily used in magnetotelluric (MT) sounding and marine controlled source electromagnetics (MCSEM). However, the high operational costs of deploying OBEMs require thorough pre-deployment testing to enhance the data reliability and quality. Commercial signal generators used for MT and controlled source electromagnetic (CSEM) testing often fall short of the restricted terms of the frequency range, signal-to-noise ratio, storage depth, time synchronization, and amplitude dynamics. To address these limitations, we developed a specialized marine MT and CSEM signal simulative generator. The generator employs pseudorandom number code-based white noise to simulate MT signals and uses multi-frequency synthesis and amplitude modulation (AM) to generate CSEM signals. The system is developed using a low-power microcontroller unit and a field programmable gate array platform, integrating various circuits such as power, clock, encoding, control, data storage, chopper, and amplification circuits. The generator simultaneously outputs four-channel white noise and AM signals. The white noise feature provides a wide and adjustable frequency band and amplitude, while the AM feature provides a large dynamic amplitude range and multi-frequency synthesis at various carrier frequency points. Comprehensive testing verified the performance of the proposed simulative generator. The test results demonstrate that the MT simulated signals cover a frequency range from 1 E4s to 100 Hz, providing adjustable amplitudes between 10 μVpp and 10 mVpp. The CSEM simulated signals include standard square waves, third harmonic waves, and seventh harmonic waves, with amplitudes adjustable from 10 mVpp to 10 Vpp. The proposed simulative generator enhances the efficiency of OBEM functional testing and provides essential equipment support for maintaining the quality of marine data. [ABSTRACT FROM AUTHOR]

Subsurface energy resources are often found in three‐dimensional and non‐spatially continuous rock formations that exhibit electrical anisotropy. Deep‐sensing tri‐axial borehole electromagnetic measurements are currently being used to detect three‐dimensional fluid‐bearing subsurface formations, but borehole environmental, geometrical and instrument‐design factors, together with measurement noise, constrain their practical range of detection and spatial resolution. By understanding the interplay of the above factors on the detectability and sensitivity of borehole deep electromagnetic measurements, one can potentially quantify the uncertainty of both target spatial location (relative to the well trajectory) and electrical resistivity contrast, thereby improving the certainty of three‐dimensional well navigation in real time. We implement a finite‐volume method to numerically solve Maxwell's equations for three‐dimensional electrically anisotropic heterogeneous rock formations in the calculation of magnetic fields measured with deep‐sensing tri‐axial borehole electromagnetic instruments. The calculated magnetic fields at measurement locations are described as the per cent difference between measurements acquired in rock formations with and without conductive or resistive three‐dimensional targets. We quantify the maximum radial distance of detection from the well trajectory and the spatial sensitivity of a commercially available deep‐sensing electromagnetic instrument with respect to environmental factors and measurement acquisition parameters by assuming that the borehole electromagnetic instrument can reliably detect offset three‐dimensional targets if the corresponding per cent measurement difference exceeds the threshold for measurement noise. Results indicate that commercially available tri‐axial deep‐sensing borehole electromagnetic instruments can achieve maximum detection distances between a quarter of and a full transmitter–receiver spacing. In addition, we show that radial detection distances vary from 0.3 to 2 skin depths depending on the geological environment, that is, target conductivity contrast with respect to the embedding background, electrical anisotropy of the background formation and targets and measurement acquisition parameters, that is, frequency and transmitter–receiver spacings. The above findings are not only important for instrument design and measurement‐acquisition planning but also for the effective implementation of real‐time inversion‐based measurement interpretation procedures. [ABSTRACT FROM AUTHOR]

Fe−6.5%Si has higher electrical resistivity, lower magnetocrystalline anisotropy, and lower magnetostriction than traditional Fe−3.2%Si silicon steel. The reduced iron losses of Fe−6.5%Si render it a highly favorable candidate for high-speed motors and transformers. However, large-scale production of wide Fe−6.5%Si tape by rapid solidification can be challenging mainly because of its high melting point. In this work, boron is alloyed to Fe−6.5%Si to reduce its melting temperature and interfacial energy to improve the alloy's processability. Boron additions from 0.01 wt.% to 2.24 wt.% into Fe−6.5%Si and its effect on ribbon thickness, grain size, magnetic, and mechanical properties were studied. Minor boron alloying significantly changed the melt pool stability and wetting on the quench wheel and in turn increased the quench rate with minimum impact on the magnetic saturation and ductility. Boron addition of < 0.06 wt.% was also found beneficial to the magnetic property of the alloy by lowering both its hysteresis and eddy current losses. [ABSTRACT FROM AUTHOR]

On January 1, 2024, a strong earthquake occurred in Japan, causing deaths and damage to Japanese infrastructure. This study discusses the electromagnetic and solar signals that anticipated the strong earthquake. This earthquake was preceded by a series of electromagnetic signals recorded by the RDF network developed by the Radio Emissions Project in Italy and by peculiar solar activity that occurred in the days before the disastrous quake. The authors believe that there may be a relationship linking telluric activity with space weather, evidenced by electromagnetic signals detectable in the phases preceding the earthquake in a time window of about five days. The results of the experiment show that the data can be compared with other known cases in the scientific literature, in the context of a crustal diagnosis and seismic precursor candidates. [ABSTRACT FROM AUTHOR]

Induced polarization datasets, which assess the overvoltage characteristics of the subsurface, are becoming increasingly prevalent. These datasets are not limited to mineral resource exploration but are also gaining traction in various engineering applications. We present the result of joint inversion of direct current resistivity and induced polarization data. We have obtained two subsurface properties: electrical resistivity and chargeability, by minimizing the single objective function. For this purpose, we have computed the distorted apparent resistivity using the secondary voltage measure at each time gate. We compared our results with the conventional inversion of induced polarization on synthetic data with both high and low chargeable mineralized ore bodies. We noted that our approach provides a more reasonable model for high chargeable ore bodies. However, both joint inversion and nonlinear approaches give similar results for low-chargeable ore bodies. Nonlinear inversion of induced polarization was accomplished by solving two objective functions: One for resistivity and another one for induced polarization. Thus, error in the resistivity inversion propagates in the chargeability computation due to consequences. Further, the developed joint inversion algorithm is also applied to a field data set measured at the Beldih mine located in the West Bengal, India. We compared our final chargeability models with the local geology and geologic models obtained via other geophysical methods on the same profiles and found an excellent correlation in both models. [ABSTRACT FROM AUTHOR]

In this study, a deep learning algorithm was applied to two-dimensional magnetotelluric (MT) data inversion. Compared with the traditional linear iterative inversion methods, the MT inversion method based on convolutional neural networks (CNN) does not rely on the selection of the initial model parameters and does not fall into the local optima. Although the CNN inversion models can provide a clear electrical interface division, their inversion results may remain prone to abrupt electrical interfaces as opposed to the actual underground electrical situation. To solve this issue, a neural network with a residual network architecture (ResNet-50) was constructed in this study. With the apparent resistivity and phase pseudo-section data as the inputs and with the resistivity parameters of the geoelectric model as the training labels, the modified ResNet-50 model was trained end-to-end for producing samples according to the corresponding production strategy of the study area. Through experiments, the training of the ResNet-50 with the dice loss function effectively solved the issue of over-segmentation of the electrical interface by the cross-entropy function, avoided its abrupt inversion, and overcame the computational inefficiency of the traditional iterative methods. The proposed algorithm was validated against MT data measured from a geothermal field prospect in Huanggang, Hubei Province, which showed that the deep learning method has opened up broad prospects in the field of MT data inversion.

Magnetotelluric (MT) forward modeling is essential in geophysical exploration, enabling the investigation of the Earth’s subsurface electrical conductivity. Traditional finite difference methods (FDMs) typically use uniform grids, which can be computationally inefficient and fail to accurately capture complex geological structures. This study addresses these challenges by introducing a non-uniform grid-based FDM for MT forward modeling. The proposed method optimizes computational resources by varying grid resolution, offering finer grids in areas with complex geology and coarser grids in more homogeneous regions. We apply this method to both typical synthetic models and a complex fault structure case study, demonstrating its capability to accurately resolve subsurface features while reducing computational costs. The results highlight the method’s effectiveness in capturing fine-scale details that are often missed by uniform grid approaches. The conclusions drawn from this study suggest that the non-uniform grid FDM not only improves the accuracy of MT modeling but also enhances its efficiency, making it a valuable tool for geophysical exploration in challenging environments.

The spatiotemporal evolution of earthquakes induced by fluid injections into the subsurface can be erratic owing to the complexity of the physical process. To effectively mitigate the associated hazard and to draft appropriate regulatory strategies, a detailed understanding of how induced seismicity may evolve is needed. In this work, we build on the well-established continuous-time random walk (CTRW) theory to develop a purely stochastic framework that can delineate the essential characteristics of this process. We use data from the 2003 and 2012 hydraulic stimulations in the Cooper Basin geothermal field that induced thousands of microearthquakes to test and demonstrate the applicability of the model. Induced seismicity in the Cooper Basin shows all the characteristics of subdiffusion, as indicated by the fractional order power-law growth of the mean square displacement with time and broad waiting-time distributions with algebraic tails. We further use an appropriate master equation and the time-fractional diffusion equation to map the spatiotemporal evolution of seismicity. The results show good agreement between the model and the data regarding the peak earthquake concentration close to the two injection wells and the stretched exponential relaxation of seismicity with distance, suggesting that the CTRW model can be efficiently incorporated into induced seismicity forecasting. [ABSTRACT FROM AUTHOR]

The magnetotelluric (MT) method is a widely used geophysical technique for deep structure exploration. However, rapid industrial development has resulted in significant anthropogenic interference for practical applications of this method in recent years. To carry out MT survey in regions with strong electromagnetic (EM) noise, we develop a strategy, in which part of MT sites are set for night time period and a newly proposed automatic clustering method based on MT signal patterns is applied to process measured data from Yingde area in Guangdong. The MT sites are employed in night time to avoid human activity and measure the quiet time MT signal to make sure that we can capture portion of MT signal. Based on cosine similarity, we can use clustering algorithms to separate the signals from the noise. The application of this strategy for geothermal exploration in Yingde area in Guangdong, indicates the validity of our proposed strategy for real geothermal detection. [ABSTRACT FROM AUTHOR]

The Weihe Basin, located in central China, stands out for its significant earthquake activity while concurrently harboring promising geothermal reservoirs. The potential association between these two geological occurrences and the underlying mechanisms remain enigmatic. Here, we compile a catalog of historic earthquakes, total strain data, data related to crustal mantle structure, surface heat flow data, and heat production data of the rocks in the Weihe Basin. Our aim is to unveil the intricate interplay among the occurrence of earthquakes, tectonic activity, and the genesis of geothermal resources. Our findings reveal that earthquake activity in the Weihe Basin is regulated by the responses of faults or fractures intricately influenced by regional tectonics. These tectonic processes are responsible for the formation of favorable geothermal resources beneath the basin. We propose there is a weak zone beneath the basin, which is controlled by a combination of tectonic processes and the flow of the asthenosphere. We finally establish a comprehensive model to visualize the genesis of the occurrence of earthquakes and the formation of geothermal resources. These results have important guiding significance for future research endeavors in the realms of both geothermal exploration and earthquake investigations within the Weihe Basin. [ABSTRACT FROM AUTHOR]

The controlled source audio-frequency magnetotelluric method (CSAMT) stands out for its economic efficiency and widespread application in geophysical monitoring. However, the separate inversion of time-lapse monitoring data encounters challenges in comparing and identifying abnormal changes due to variations in data fitting. Furthermore, the utilization of a method akin to Cagniard apparent resistivity for inversion necessitates the simultaneous observation of at least two components of the electromagnetic field, making it unsuitable for extensive three-dimensional observations. This paper proposes a 3D time-lapse electric field inversion algorithm for CSAMT, addressing the complexities in geophysical monitoring. The algorithm introduces two regularization factors and defines an objective function with both temporal and spatial constraints. Synthetic testing reveals the stability of the 3D time-lapse electric field inversion algorithm, demonstrating its effectiveness in delineating underground variations. This solution resolves the challenges posed by the independent inversion of time-lapse monitoring data. [ABSTRACT FROM AUTHOR]

In 2018 the first subglacial lake in the Canadian Artic was proposed to exist beneath Devon Ice cap, based on the analysis of airborne radar data. Here, we report a new interpretation of the subglacial material beneath Devon Ice Cap, supported by data acquired from multiple surface-based geophysical methods in 2022. The geophysical data recorded included 9 km of active source seismic reflection profiles, 7 transient electromagnetic soundings and 17 magnetotellurics stations. These surface-based geophysical datasets were collected above the inferred locations of the subglacial lakes and show no evidence for the presence of subglacial water. The acoustic impedance of the subglacial material, estimated from the seismic data, is 9.49 ± 1.92 x 106 kg m-2 s-1, comparable to consolidated or frozen sediment. The resistivity models obtained by inversion of both the transient electromagnetic and magnetotelluric measurements show the presence of highly resistive rock layers (1000 – 100000 Ω.m) directly beneath the ice. Re-evaluation of the airborne reflectivity data show that the radar attenuation rates were likely overestimated, leading to an overestimation of the basal reflectivity in the original radar studies. Here, we derive new radar attenuation rates using the temperature- and chemistry-dependent Arrhenius equation, and when applied to correct the returned bed power, the bed power does not meet the basal reflectivity threshold expected over subglacial water. Thus, the radar interpretation is now consistent with the seismic and electromagnetic observations of dry or frozen, non-conductive basal material. [ABSTRACT FROM AUTHOR]

A silicon nanocrystal (Si NC) white light-emitting (λ = ∼400–900 nm) thin film with a relatively low resistivity of 1.6 × 104 Ω m has been prepared as an active medium for electrically driven Si light sources. The average size of Si NC is 2.4 ± 0.4 nm. To enhance the light emission efficiency of this low-resistivity Si NC thin film, approach of hydrogen passivation suitable for the traditional high-resistivity (1.2 × 107 Ω m in this work for example) red light-emitting Si NC thin film has been tried and found unavailable unfortunately. Our first principles simulation shows that Si NCs bonded to −O, −NH2, −OH, and −H ligands are responsible for red, green, and blue (RGB) primary color emissions in this white light-emitting sample, respectively. Passivation of the sample in NH3 and H2O atmosphere is then conducted, aiming to increase the number of the RGB light emitters. The light emission is significantly enhanced, with photoluminescence intensity, photoluminescence quantum yield, electroluminescence intensity, and net optical gains increased by factors of 4.6, 4.2, 4.0, and ∼3.0, respectively, after 10-day passivation. Further enhancements are expected for longer passivation. [ABSTRACT FROM AUTHOR]

To reveal the deep seismogenic environment and mechanism of earthquakes in Songyuan City, Northeastern China, 59 broadband magnetotelluric sites in the Songyuan area were arranged in this study at a spacing of 5 km. In addition, two intersecting magnetotelluric profiles, with a total of 23 measuring sites and a spacing of 2 km, were established near the Ningjiang earthquake swarm. Using a nonlinear conjugate gradient (NLCG) algorithm, resistivity structures in the lithosphere were obtained at different scales using three-dimensional (3D) inversion. The research results show that: a deep high-conductivity system (<10 Ω·m) was identified at 25–85 km depth in the lithosphere under Songyuan, corresponding closely to a region of high heat flow. It is inferred to be the molten material of mantle upwelling. In addition, a shallow high-conductivity system (<10 Ω·m) was identified beneath the Ningjiang earthquake swarm, which is interpreted to correspond to the Fuyu North fault. It is the main seismo-controlling structure of the Ningjiang earthquake swarm. The deep seismogenic environment and seismogenic mechanism of the Ningjiang earthquake swarm can be described as a deep upwelling of molten mantle material, which provides the power source. The deep magma intruded into the lower crust and accumulated, then intruded along faults and fissures, resulting in the activation of the North Fuyu fault and triggering the Ningjiang earthquake. It is attributed to the activation of shallow faults caused by the upwelling of molten mantle material. [ABSTRACT FROM AUTHOR]

By means of three-dimensional resistive-magnetohydrodynamical models, we study the evolution of the so-called dead zones focused on the magnitude of the Reynolds and Maxwell stresses. We consider two different types of static resistivity radial profiles that give rise to an intermediate dead zone or an intermediate active zone. As we are interested in analysing the strength of angular momentum transport in these intermediate regions of the disc, we use as free parameters the radial extent of the intermediate dead (Δ r idz) or active (Δ r iact) zones, and the widths of the inner (⁠|$H_{b_1}$|⁠) and outer (⁠|$H_{b_2}$|⁠) transitions. We find that regardless of the width or radial extent of the intermediate zones, Rossby wave instability (RWI) develops at these transition boundaries, leading to the emergence of vortices and spiral waves. In the case of an intermediate dead zone when |$H_{b_1}\,H_{b_2}\le 0.8$|⁠ , the vortices are almost completely confined to the dead zone. Remarkably, we find that the formation of vortices at the inner transition can drag magnetic field lines into the dead zone stirring up the region that the vortex covers (reaching an α ≈ 10−2 value similar to that of an active zone). Vortices formed in the outer transition only modify the Reynolds stress tensor. Our results can be important to understanding angular momentum transport in poorly ionized regions within the disc due to magnetized vortices within dead zones. [ABSTRACT FROM AUTHOR]

Gravity surveys constitute an important method for investigating the Earth's interior based on density contrasts related to Earth material differentials. Because lithology depends on the environment and the period of formation, there are generally clear boundaries between rocks with different lithologies. Inversions with convex functions for approximating the L 0 norm are used to detect boundaries in reconstructed models. Optimizations can easily be found because of the convex transformations; however, the volume of the reconstructed model depends on the weighting parameter and the density constraint rather than the model sparsity. To determine and adapt the modelling size, a novel non-convex framework for gravity inversion is proposed. The proposed optimization aims to directly reduce the L 0 norm of the density matrix. An improved iterative hard thresholding algorithm is developed to linearly reduce the L 0 penalty during the inner iteration. Accordingly, it is possible to determine the modelling scale during the iteration and achieve an expected scale for the reconstructed model. Both simple and complex model experiments demonstrate that the proposed method efficiently reconstructs models. In addition, granites formed during the Yanshanian and Indosinian periods in the Nanling region, China, are reconstructed according to the modelling size evaluated in agreement with the magnetotelluric profile and density statistics of rock samples. The known ores occur at the contact zones between the sedimentary rocks and the reconstructed Yanshanian granites. The ore-forming bodies, periods, and processes are identified, providing guidance for further deep resource exploration in the study area. [ABSTRACT FROM AUTHOR]

The electrical resistivity method is widely used in near-surface mineral exploration. At present, the deterministic algorithm is commonly employed in three-dimensional (3-D) electrical resistivity inversion to obtain subsurface electrical structures. However, the accuracy and efficiency of deterministic inversion rely on the initial model. In practice, obtaining an initial model that approximates the true subsurface electrical structures remains challenging. To address this issue, we introduce a broad learning (BL) network to determine the initial model and utilize the limited memory quasi-Newton (L-BFGS) algorithm to conduct the 3-D electrical resistivity inversion task. The powerful mapping capability of the BL network enables one to find the model that elucidates the actual observed data. The single-layer BL network makes it efficient and easy to realize, leading to much faster network training compared to that using the deep learning network. Both the synthetic and field experiments suggest that the BL framework could effectively obtain the initial model based on observed data. Furthermore, in comparison to using a homogeneous medium as the initial model, the L-BFGS inversion with the BL framework-designed initial model improves the inversion accuracy of subsurface electrical structures and expedites the convergence speed of the iteration. This study provides an effective approach for fast initial model design in a data-driven manner when the prior information is unavailable. The proposed method can be useful in high-precision imaging of near-surface mineral electrical structures. [ABSTRACT FROM AUTHOR]

The tectonic position of the southwest section of the Qinzhou Bay-Hangzhou Bay Tectonic Junction Zone (QHTJZ) can be determined by examining the Qinzhou-Fangcheng Junction Zone (QFJZ) in Guangxi. This zone is significant because it was the location of the largest earthquake ever recorded in the inland region of South China, specifically the 1936 LingshanM6¾ earthquake in Guangxi. Therefore, this region serves as an optimal location for researching the origins of intraplate earthquakes in South China. This study presents a display of a broadband magnetotelluric (MT) prospecting profile that traverses the Guangxi QFJZ and the Lingshan earthquake zone, extending from the northwest (NW) to the southeast (SE). A resistivity structure model was generated using three-dimensional (3D) inversion technology along the profile. The main faults in QFJZ were analyzed in terms of their deep extension forms and tectonic attributes. This analysis was performed by integrating the results obtained from geology, gravity, wave velocity ratio, Global Position System (GPS), and geothermal flow. The results showed that (1) the Dongzhong-Xiaodong fault (DXf), the eastern Fangcheng-Lingshan fault (FLf2), and the eastern Hepu-Beiliu fault (HBf2) were all trans-crustal deep faults, and crust-mantle ductile shear zones developed in the deep part. Two electrical boundary zones, DXf and HBf2, were identified. DXf inclined towards the northwest, while HBf2 inclined towards the southeast. The Fangcheng-Lingshan fault (FLf) exhibits a tectonic style resembling a "flower" shape in the upper crust. In the deeper section, it is characterized by an electrical boundary zone that gradually slopes towards the southeast direction. (2) The Hunan-Guangxi Passive Continental Margin (HGPCM) on the NW side of DXf had a stratified resistivity structure and relatively stable Bouguer gravity anomalies, which conformed to the quasi-craton tectonic attribute of the local failure at the southeastern margin of the Yangtze Block (YB). The southeastern side of this block is marked by the presence of the QFJZ and Yunkai Magmatic Arc (YKMA). These areas exhibit varying Bouguer gravity anomalies, indicating a combination of high and low resistivity in their electrical structures. This suggests that this zone has undergone multiple stages of structural evolution and transformation. The giant high-resistivity body under the Qinzhou-Fangcheng Remnant Ocean Basin (QFROB) might be the trace left by the extinction of the South China Ocean and the collision orogeny between YB and the Cathaysian Block (CB). The presence of sub-low-resistivity layers in the middle-lower crust between the Liuwandashan Magmatic Arc (LMA) and YKMA indicates that this particular zone is being influenced from a distance by magmatic activities originating from the Leiqiong mantle. (3) The focal area of the 1936 Lingshan earthquake was located in the brittle high-resistivity body with a low strain rate. Under the coupling action of NWW-SEE regional tectonic stress and deep thermodynamic force, the brittle high-resistivity body in the upper crust became the main body for accumulating the tectonic stress. The Lingshan earthquake occurred due to the dextral strike-slip fracture instability of FLf2, a rock layer with slightly lower strength in the sub-high-resistivity zone. This instability was triggered when the accumulated stress reached the ultimate rock strength. The unveiling of the seismogenic model of the Lingshan earthquake, as presented in this study, holds significant scientific importance in comprehending the factors contributing to intraplate earthquakes in the South China region. [ABSTRACT FROM AUTHOR]

Electrodes are used to measure a potential difference between two points. In geophysical and geotechnical applications they are often in the form of non‐polarizable porous‐pot electrodes. Here we describe the design, construction, and testing of modular and refillable electrodes, which facilitates repair as the electrodes degrade over time. We use a chemical composition based on a metal in contact with an over‐saturated electrolyte that consists of a salt of that metal and an auxiliary salt. We compare characteristics when the electrolyte is stabilized in a clay or not, and with various states of ceramic porous plugs and two types of wood plugs. Next, we assess the long‐term stability (more than 1 month), noise (periods of 1 s to 1 hr), and temperature sensitivity of different types of electrodes. Electrodes with an electrolyte and clay formula showed lower noise (0.2–0.4 μV at periods of 1–120 s), greater long‐term stability (0.05–0.5 mV/month of smooth drift), and greater consistency between samples measured than those with no clay (noise and drift values up to four times larger). The effects from different porous plugs were negligible, with similar results for ceramic and wood types. The temperature sensitivity of the electric potential was assessed, from −3 to 35°C. All electrodes showed a temperature sensitivity of about −30 μV/°C. This is considered very low compared to some commercially available electrodes. Finally, continuous long‐term laboratory and field measurements of the potential highlight the application of the new electrodes. Key Points: Development of a modular, repairable, refillable porous‐pot electrode with an over‐saturated electrolyte, preferably stabilized in clayLong‐term measurements reveal (a) high stability, (b) smooth drift, <0.5 mV/month, and (c) low noise, 0.2–0.4 μV at a period of 1–120 sExperiments from −3 to 35°C determine a temperature sensitivity of the electric potential of about −30 μV/°C, which is considered low [ABSTRACT FROM AUTHOR]

The Bakreswar geothermal province represents a medium enthalpy geothermal system with its Bakreswar and Tantloie hot springs. It lies within the Chotanagpur Granite Gneissic Complex in the eastern part of the Indian Peninsula. The province has a high heat flow and a high geothermal gradient of 90°C/km. Magnetotelluric data from 95 sites in a frequency range of 10 kHz–10 Hz were acquired over the Bakreswar geothermal province to obtain an electrical conductivity model and map the geothermal reservoir with its fluid pathways and related geological structures. Subsurface conductivity models obtained from three‐dimensional inversions of the Magnetotelluric data exhibit several prominent anomalies, which are supplemented by gravity results. The conductivity model maps three features which act as a conduit (a) a northwest–southeast trending feature, (b) an east–west trending feature to the south of the northwest–southeast trending feature (which lies 1 km north of the Oil and Natural Gas Corporation fault marked by previous studies) and (c) shallow conducting features close to Bakreswar hot spring. The northwest–southeast trending feature coincides with the boundary of the high‐density intrusive block. This northwest–southeast trending feature provides the pathway for the meteoric water to reach a maximum depth of 2.7 km, where it gets heated by interacting with deep‐seated structures and then it rises towards the surface. The radiogenic process occurring within the granites of Chotanagpur Granite Gneissic Complex provides the heat responsible for heating the meteoric water. The northwest–southeast and east–west trending features are responsible for the transport of meteoric water to deeper depths and then towards the shallow regions of the Earth. The near surface features close to the Bakreswar hot spring are responsible for carrying the water further towards the hot spring. The resistivity of these structures plotted as a function of salinity and temperatures for saline crustal fluids suggests the involvement of meteoric water. Further, applying Archie's law to this resistivity suggests that the conduit path has a porosity greater than 10%. This study successfully maps the anomalous structures which might foster the migration of geothermal fluid in Bakreswar geothermal province. [ABSTRACT FROM AUTHOR]

Hydraulic fracturing, a significant contributor to seismic activity within and around operational fields, has been extensively used in shale gas production. Magnetotelluric (MT) sounding is an effective geophysical tool for identifying high-conductivity fluid-filled and/or molten regions. In this study, we deploy a dense grid of rectangular MT sites to investigate the 3D geoelectrical resistivity structure beneath the Weiyuan shale gas block (WSGB) and subsequently examine the causes of seismic activity. The resistivity data, obtained through 3D inversion accounting for topography using ModEM, reveals a shallow low-resistivity layer (<10 Ω-m) within the WSGB, ranging from ∼2 to 5 km in depth. This layer exhibits multiple isolated areas with very low resistivity (<5 Ω-m), indicative of fluid-filled zones associated with hydraulic fracturing or shale gas-bearing formations. In the northwestern WSGB, the Weiyuan anticline presents a high-resistivity dome extending possibly to depths beyond 20 km, without extending beyond the northern boundary of our study area. Conversely, the sedimentary zone in the southeastern WSGB displays a low-resistivity feature, with an extremely low-resistivity center (<1 Ω-m). Since a consistent high-resistivity zone exists beneath each fault and its top depth is <5 km, so faults might not extend downward below 5 km. Earthquakes with magnitudes (ML) of 3.0 or higher predominantly occur close to the faults, when considering industrial production data, we found a noteworthy correlation between earthquakes with ML < 3.0 and annual shale gas production within the WSGB. Tectonic faulting is not the leading cause for ML < 3.0 earthquakes but likely the primary contributor to seismic events with ML ≥ 3.0. [ABSTRACT FROM AUTHOR]