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The direction of drilling wells in the plateau slope area is toward finding local favorable water-rich blocks, which are relative groundwater accumulation areas under the control of structure, lithology, and landform. These areas often have obvious geological boundary conditions (such as the presence of a water resisting layer in the vertical direction, the development of a fault fracture zone in the plane), and their corresponding physical boundary often has a relatively low or high resistivity to the surrounding rock. In this paper, the comprehensive geophysical method is used to study the application of water prospecting in the plateau slope of Shuangnuo village, Fuyuan, Yunnan Province. First, according to the hydrogeological conditions (the development of a fault fracture zone and clastic rock is unknown), the plane distribution range and vertical development of the low-resistivity abnormal fault fracture zone are determined using the electrical resistivity tomography (less than 100 m) and audio magnetotelluric methods (100–500 m). Vertically, the development depth and thickness of the clastic rock aquifuge (P 1 l) are determined using the audio frequency magnetotelluric method, which provides a basis for the maximum depth of the borehole layout. The combination of the electrical resistivity tomography and audio frequency magnetotelluric methods can delineate the favorable water-rich block in the study area well and verify that the study area has the prerequisite to become a water prospecting target. To determine the best location of the borehole layout, a combination of the composite profiling, microtremor horizontal-to-vertical spectral ratio (HVSR), apparent resistivity sounding, and K-reflection coefficient methods are carried out in the favorable water-rich block, which delineated by the electrical resistivity tomography and audio frequency magnetotelluric methods. The optimal borehole layout location is determined through the synchronous low resistivity anomaly of the composite profiling method, and the synchronous low resistivity anomaly is determined as a karst fracture zone (qualitative determination) in combination with the HVSR high-value anomaly of the microtremor method. The development depth of the karst fracture zone is finally determined by using the apparent resistivity sounding and K curves. This study reveals that the depth of the drilled hole is 243.5 m, and the water inflow is 144.3 m 3 / day, successfully solving the serious water shortage problem in the local area. The case study results show that the combination of geophysical prospecting methods, namely, the electrical resistivity tomography, audio frequency magnetotelluric, composite profiling, microtremor, apparent resistivity sounding, and k-reflection coefficient methods, is effective for water exploration in the plateau slope zone.

The terrain conditions and geological structure of the mountainous areas in western China are complex. To meet the design requirements for the expressway, the route adopts the design of deep-buried super-long tunnels in hilly areas. If the highway tunnel passes through faulty structures, such as improper selection of structure and foundation form, it can cause collapse and structural instability during construction. Therefore, basic characteristics of faults and information that is more accurate should be provided during the survey process to avoid subsequent problems. The frequency and magnitude of earthquakes in this study area are high and available data show that the Xiaojiang fault was still active during the Quaternary Holocene period, which is a high-risk area for earthquakes. Therefore, a set of comprehensive technologies, such as geophysical prospecting, geological survey, and drilling, and was used to identify faults and their characteristics and to visually display underground information within a certain depth range. Here, the magnetotelluric method was used to analyze the electrical characteristics and structure of the highway tunnel. In addition, the electrical characteristics and structure of the Xiaojiang fault were discussed. Geological surveys and drilling agree well with the analysis and interpretation of the research results and further proposed a processing and interpretation method for correcting the dip angle of the fault using the statistical results from the long axis dip angle of the tensor polarization map for the wave impedance. Thus, a large amount of information in the tunnel site can be effectively obtained for predicting and evaluating the Xiaojiang fault. Furthermore, our results provide strong technical support for designing and operating highway tunnels, with meaningful experience and reference for future geophysical processing and interpretation.

Loess soils are widely distributed worldwide and typical in northwest China, and excessive agricultural irrigation has caused landslides in the area, specifically in the Heifangtai loess region in Lanzhou, Gansu, China. Geophysical exploration is an essential method in landslide engineering geological surveys, and geological surveying, drilling, geophysical prospecting, monitoring, and other methods are used for performing engineering geological evaluation and obtaining comprehensive basic data for landslide protection design and construction. The theoretical feasibility of using geophysical methods in loess landslide detection is essential. On the basis of the shallow geological structure of the Heifangtai landslide region in Lanzhou, Gansu, China, a typical geoelectric model of the magnetotelluric method was established, and the loess landslide area was modeled through a two-dimensional finite element method, forward numerical simulation, and engineering geological analysis. The distribution characteristics of the magnetotelluric field were determined. This is a typical application of the geological process analysis method in geophysical exploration. This study provides the typical stratigraphic structure and electrical characteristics of different groundwater distributions in Heifangtai, Gansu, China, verifies the accuracy of forward modeling and calculation results, and provides a detailed theoretical basis for landslide detection through magnetotelluric methods. Through the numerical simulation of the forward modeling of the Heifangtai landslide region in Lanzhou, Gansu, China, this study can provide a detailed geophysical basis for landslide investigation, corroborate results of geological investigation and landslide design, and facilitate the sustainable development of agriculture in Heifangtai.

Epithermal deposits represent a significant category of gold occurrences, with their subsurface structure playing a key role in reserve assessments. Fujian Province, characterized by extensive Mesozoic volcanic activities, stands out as a noteworthy region for shallow hydrothermal mineralization in China. This paper focus on the Youxi area within Fujian Province, employing the dual-frequency induced polarization method (DFIP) and controlled-source audio-frequency magnetotelluric method (CSAMT) to investigate the target ore. The DFIP results revealed predominant northeast-oriented zones with high polarizability and notable apparent resistivity. The CSAMT data were inverted using the SCS2D software. Two-dimensional resistivity profiles reveal a three-layer electrical structure, comprising subsurface banded rhyolites influenced by fault zones, intermediate-low resistivity sandstone layers, and deep-seated high-resistivity conglomerates. The resistivity gradient zones and highly polarizable locations align closely with known local faults. We interpreted these resistivity gradient zones as prospective target areas for mineralization, a hypothesis subsequently validated by drilling results. Combining geochemical analyses of epithermal gold deposits with the electrical resistivity structure, we propose an explanatory model for the mechanism of the formation of epithermal gold–silver deposits in the Youxi area. The magmatic hydrothermal fluids ascended along the fault, underwent convection-driven interaction with meteoric waters, and subsequently metasomatized the host rocks. This integrated approach provides valuable insights into the geological processes governing epithermal gold–silver deposit formation in the Youxi region.

A wide range of terrain features and landforms, which are exemplified by intricate geological formations and diverse rock compositions, are found in the western mountainous regions of China. These areas frequently encounter geological disasters. As one of the natural disasters, landslides lead to considerable loss of human life and property. Considering mitigation of the losses caused by landslide disasters, a necessary measure for disaster prevention and mitigation involves conducting detailed investigations and monitoring of landslides, which is also the cornerstone of landslide warning. This study compares and analyzes the feasibility of the magnetotelluric detection method for landslides using the results of engineering geological surveys and landslide monitoring. The study aims to address the scientific problem of the validity of using magnetotelluric methods to detect landslide development processes. The Tangjiawan landslide signal on the left side of the K94+000~K94+145 section of the Wenma Expressway is analyzed by employing engineering geological survey, magnetotelluric detection, landslide monitoring, landslide analysis, and other methods. Analysis results provide the static electrical characteristics of lithology, structure, and groundwater, as well as the dynamic electrical characteristics of landslide development. This study focuses on analyzing the relationship between the methods of magnetotelluric detection and engineering geological surveys and the results of landslide monitoring. The workflow and methods for data collection, processing, inversion, interpretation, and analysis using the magnetotelluric method to detect the dynamic development process of landslides are presented in the conclusion. Preliminary conclusions indicate a strong correlation between the dynamic changes in magnetotelluric wave impedance with the surface displacement of landslides and the dynamic changes in groundwater. The use of the magnetotelluric method for landslide detection and monitoring is a feasible example. The research results can offer certain technical references for the detection and monitoring of landslides using magnetotelluric methods and also provide references and guidance for the selection of diversified landslide monitoring methods in the future.

The detection and evaluation of concealed mineral resources deep in metallic mines and in the surrounding areas remain technically difficult. In particular, due to the complex topographic and geomorphic conditions on the surface, the detection environments in these areas limit the choices of detection equipment and data collection devices. In this study, based on metallogenic theory and the metallogenic geological characteristics of banded iron formation (BIF)-type iron ores, equipment for surface geophysical surveys (i.e., the high-precision ground magnetic survey method, the transient electromagnetic method, and the magnetotelluric method) and data collection devices capable of taking single-point continuous measurements were employed to detect the concealed iron ore bodies in the transition zone CID-1 between the Hejia and Dumu iron deposits in the Gongchangling iron ore concentration area in the Anshan-Benxi area (Liaoyang, China), a representative area of BIF-type iron ores. The results showed that an optimal combination of these geophysical survey methods accurately determined the anomalous planar spatial locations and anomalous profile morphologies of the concealed iron ore bodies. On this basis, we determined their locations, burial depths, and scales. Two anomalous zones induced by concealed iron ore bodies, YC-1 and YC-2, were discovered in zone CID-1. Two concealed iron-bearing zones, one shallow (0–150 m) and one deep (300–450 m), were found in YC-1. A 100 m scale drilling test showed that the cumulative thickness of the shallow iron-bearing zone was over 23.6 m.

The western segment of the suture zone between the Yangtze and Cathaysia blocks, which is the most important tectonic boundary related to the formation and rifting of south China, is enigmatic and not fully understood due to the sporadic exposure of Precambrian strata and ophiolites. Three‐dimensional electrical resistivity models derived from inversion of magnetotelluric data identified a lithospheric‐scale conductive zone extending northeastwards beneath the Youjiang basin, which was interpreted as the western segment of the suture zone. The high conductivity and coincident high magnetic anomalies closely match the location of Carlin‐type gold deposits, which can be explained by fluids and gold‐bearing sulfide minerals in a fossil suture zone. Inconsistent with the southeast‐dip resolved at the eastern segment of the suture zone (the Jiangshan‐Shaoxing fault) in the earlier study, the slightly north‐dipping geometry at the western suture zone implies the reactivation by northward subduction and closure of the Paleo‐Tethys Ocean. Plain Language Summary Suture zones are tectonic scars that mark the subduction, collision, and amalgamation of different tectonic units. Imaging suture zones is critical because they are first‐order tectonic boundaries and can play a guiding role in continental rifting and breakup. The suture zone between the Yangtze and Cathaysia blocks is the most important tectonic boundary in south China. While the eastern segment of this suture zone is agreed to be located along the Jiangshan‐Shaoxing fault, the western segment of this suture zone is under debate. This study used magnetotelluric method to image the deep earth structure beneath the western boundary of the Yangtze and Cathaysia blocks. We identified a high‐conductivity zone from the subsurface to a depth of 80 km and interpreted this zone as being caused by fluids and gold‐bearing sulfide minerals in a fossil suture zone. The conductivity pattern observed in this suture zone differs from that in the earlier study about the eastern segment of the suture zone. This implies that the western suture zone has been modified after the initial collision of the two continents, perhaps by northward subduction and closure of the Paleo‐Tethys Ocean. Key Points Magnetotelluric array data were inverted to obtain the lithospheric resistivity structure in southwestern China Three‐dimensional resistivity model images a Precambrian suture beneath the Youjiang basin The geometry resolved at the suture zone implies the reactivation by northward subduction and closure of the Paleo‐Tethys Ocean

The Northern Tanzanian Divergence in the East Africa Rift is arguably the best place on Earth to study the controls on rifting of thick lithosphere. Here, where the East Africa Rift intersects the Tanzanian Craton and the Mozambique Belt, the relationships between volcanism, faulting, pre‐existing structures and lithospheric thickness and composition can be observed. In this work, we carry out the first lithospheric‐scale 3D magnetotelluric modeling of the Northern Tanzanian Divergence and combine the results with experimental electrical conductivity and petrology models to calculate mantle composition, which is also inferred in the craton from reanalysis of garnet xenocryst data. Our results show that metasomatic materials exist in the cratonic lithospheric mantle and the relatively undeveloped southern part of the rift zone. However, the lithospheric mantle of the Mozambique Belt and the more developed northern section of the rift is more resistive and does not contain metasomatic phases. Combined with geochemical data from erupted lavas, these results suggest that, in zones that have experienced voluminous Cenozoic magmatism, melting events have destroyed the metasomes and dehydrated the mantle. Since the presence of magma is a primary control of lithospheric strength, rifting may become limited as the lithospheric mantle becomes dehydrated and harder to melt. Plain Language Summary The motion of tectonic plates relies on a specific set of physical conditions. Continental breakup or rifting occurs when certain parts of the lithosphere are weak, and when stress applied to these regions is sufficient. Weaknesses in the lithosphere rely on its composition and pre‐existing structures. We can image and analyze these features using the magnetotelluric method, a geophysical technique that maps electrical conductivity variations within the Earth. Our results show that compositionally weakening agents (metasomes) play an essential role in the development of the rift by making the mantle easier to melt. We also image some portions of the rift that do not contain such agents, suggesting that melts may have dried out these parts of the lithosphere, leaving a dry and resistive residue. This situation may indicate that melting in the region might be limited in the long run due to the absence of these materials. Key Points 3D magnetotelluric models of North Tanzanian Divergence are converted to water in mantle models to map metasomatism in the region Melting events in the Mozambique Belt caused metasomes to be destroyed and the lithospheric mantle to be dehydrated The rifting in the region might be limited if there is no supply of metasomatic material toward the rift zone

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 systems Regional groundwater circulation conveys significant amounts of water, energy, and solutes through relatively impervious depths Magnetotelluric surveys can potentially map the resistivity patterns created by the solute concentration patterns within the mountain block

The North China Craton is the oldest continental block, and has suffered from large-scale lithospheric thinning and destruction, which in turn led to gold deposits in northern China. The decratonic gold deposits in the North China Craton became the most important gold deposits in China, and geophysical methods are key means to detect and discover gold deposits there. In this paper, based on the geological and petrophysical characteristics of the North China Craton, the geological model of the decratonic gold deposits is transformed into a geophysical model. At present, two methods of geophysical exploration of decratonic gold deposits are in use: rapid and efficient exploration on the scale of the ore concentration area, and large depth exploration on the scale of the deposit area. In detail, the airborne electromagnetic, magnetic and gravity methods are used to detect the shallow (1,500 m) anomaly area on the scale of the ore concentration area. Through the ground-controlled source electromagnetic and ground magnetotelluric methods, explorations for targets at significant depth (5,000 m) are carried out in the mining area. Then, taking the Liaodong ore concentration area as an example, geophysical methods are used to discover two prospecting areas around the Jianshanzi Fault in the Qingchengzi ore concentration area, Baiyun-Xiaotongjiapuzi deep prospecting area, and Qingchengzi deep prospecting area. Next, three prospecting areas are delineated around the Jixingou Fault in the Wulong mining area, Wulong deep prospecting area, Weishagou deep prospecting area, and Chang’an deep prospecting area. The anomalies in the ore concentration area and mining area are revealed by means of three-dimensional exploration methods, thereby providing technical support for the exploration of metal minerals such as decratonic gold deposits.