Search

Landslides are a type of natural disaster that can cause substantial harm to humanity. Monitoring and predicting the initiation of potential landslides is critical to avoiding losses due to disasters and economic activities. The impact of the controlled-source audio-frequency magnetotelluric method on investigating landslide surfaces is assessed through numerical simulations with a finite element approach. A Dirichlet boundary condition is selected to match the truncated boundary, resulting in a remarkable improvement in simulation efficiency. Rederivation of the formulas for a layered medium adept to the controlled-source audio-frequency magnetotelluric method is necessary to determine the electromagnetic field at any location along the truncated boundary. After the reliability evaluation of the new codes, a landslide model with a slide surface is designed, and the characteristics of its electromagnetic field and the apparent resistivity are studied. Instead of the total electromagnetic field, which is strongly influenced by topography variation, the apparent resistivity should be used for sliding surface detection. The normalized pure anomalous electromagnetic field may also be employed to quickly assess the detectability of the sliding surface. Overall, this study demonstrates that the controlled-source audio-frequency magnetotelluric method can be employed for investigating landslides, and recommends survey parameters, including configuration, frequency range, and length of survey line in landslide exploration. [ABSTRACT FROM AUTHOR]

Yangshan gold belt (YSGB) in Gansu Province is a super‐large orogenic gold deposit located in the middle section of the Mianxian‐Lueyang arcuate suture zone (Mian‐Lue suture zone). The YSGB is mainly divided into the Gejiaowan, Anba, and Gaoloushan mine sections. The ore veins are strictly controlled by strong strain zones in the fracture zone and secondary fractures superimposed on the inherited activity and are vein‐like in general and lenticular in localities. For a long time, there have been different understandings regarding its ore‐controlling factors and mineral genesis. By utilizing controlled‐source audio‐frequency magnetotellurics (CSAMT) technology to conduct electrical characteristic studies, the deep electrical structural characteristics of the Gaoloushan section are identified, and a tectonically‐controlled geoelectric model of the deposit is established, which provides geophysical evidence for the view that the Yangshan gold mine is a tectonically‐controlled low‐temperature hydrothermal deposit in altered rock, guiding the arrangement of exploration work and identifying prospective mining areas, and thereby providing a geophysical exploration paradigm for deep exploration of large orogenic gold deposits. [ABSTRACT FROM AUTHOR]

Objective The aim of this study is to characterize the deep electrical structure of the Baishawo pegmatite-type deposits, explore the spatial distribution of rare metal mineralization models and ore-conferring carriers, and elucidate the relationship between the location of ore veins to provide a basis for prediction in rare metal mineral exploration. Methods Through the controlled-source audio-geomagnetic method (CSAMT) and the conjugate gradient method of inverse measurement of three exploration profiles, deep hidden rock (ore) bodies were detected. Then, by combining these results with the information from drill holes and elemental geochemical anomalies, a comprehensive analysis was carried out to reveal the distribution of the hidden dikes and the mineralization characteristics. Results The study showed that the concealed pegmatite veins are mainly located in the Lengjiaxi Group, where they are concentrated on the top of the granite body and around tectonic fissures and have burial depths ranging from 50 to 300 m. The geophysical signature of pegmatite vein mineralization is a high-resistance vein-like geologic body intruded from a deep high-resistance body into a shallow low-resistance body. Conclusion The determined distribution and burial depth of concealed pegmatite veins, identified potential concealed veins in the study area, and geophysical characteristics of the pegmatite vein mineralization provide a basis for understanding the formation mechanism of fracture zone-constrained pegmatite veins. Significance The research results provide a scientific basis for follow-up exploration of the Baishawo deposit, reveal the formation mechanism of the pegmatite veins, and provide reliable physical exploration and prediction technology and experience useful for rare metal exploration in northeast Hunan and south China.

Copyright of Journal of Geomechanics is the property of Journal of Geomechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Mining Magazine is the property of China Mining Magazine Co., Ltd. and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The development of geothermal energy has received extensive attention because of global energy scarcity and environmental pollution. The Tangquan area is in the north of the Yangtze fold belt, and the lack of magmatic rock development has resulted in a low-temperature type of geothermal reservoir. There are sporadic hot springs and cold springs exposed in the study area, but the uncertain deep geological structure, unknown geothermal reservoir formation mechanism, and lack of detailed exploration data seriously restrict the exploration and development of geothermal resources in the area. Filling underground faults with water can significantly reduce electrical resistivity, while traps filled with warm water can cause a decrease in S-wave velocity. Thus, a new integrated geophysical method, including the controlled source audio-frequency magnetotelluric (CSAMT) and microtremor methods, is applied for geothermal exploration in the region. The combination of CSAMT and microtremor methods can determine thermal-controlled and water-conducting structures more effectively and locate geothermal storage more accurately. The source, channel, storage, and cover of regional geothermal reservoir formation are analyzed using geophysical and geological data. That is, the regional NE- and NW-trending faults are explained as thermal-controlled and water-conducted structures, respectively. The deep Sinian Dengying Formation supplies a heatand water-bearing space. The tectonic intersection area, especially the tensional fault zone, is found to be closely related to the existence of geothermal reservoirs, which is well verified by later drilling results. Finally, a geothermal reservoir model is established to comprehensively understand the distribution of geothermal energy in the region. [ABSTRACT FROM AUTHOR]

Traditional methods for monitoring the foundation settlement of airport runways predominantly employ equipment such as leveling instruments, total stations, layered settlement instruments, magnetic ring settlement instruments, ground-penetrating radar (GPR), and synthetic aperture radar. These methods suffer from low automation levels, are time-consuming, labor-intensive, and can significantly disrupt airport operations. An alternative electromagnetic detection technique, Controlled Source Audio-Frequency Magnetotellurics (CSAMT), offers deep-depth detection capabilities. However, CSAMT faces significant challenges, particularly in generating high signal-to-noise ratio (SNR) signals in the far-field region (FfR). Traditional CSAMT utilizes grounded horizontal dipoles (GHDs), which radiate symmetric beams. Due to the low directivity of GHDs, only a small fraction of the radiated energy is effectively utilized in FfR observations. Enhancing the SNR in FfR typically requires either reducing the transceiving distance or increasing the transmitting power, both of which introduce substantial complications. This paper proposes an airborne-dangled monopole-antenna symmetric remote-sensing radiation source for airport runway monitoring, which replaces the conventional GHD. The analytical, simulation, and experimental verification results indicate that the energy required by the airborne-dangled symmetric source to generate the same electric field amplitude in the FfR is only one-third of that needed by traditional CSAMT. This results in significant energy savings and reduced emissions, underscoring the advantages of the airborne-dangled monopole-antenna symmetric source in enhancing energy efficiency for CSAMT. The theoretical analysis, simulations, and experimental results consistently verify the validity and efficacy of the proposed airborne-dangled monopole-antenna symmetric remote-sensing radiation source in CSAMT. This innovative approach holds substantial promise for airport runway monitoring, offering a more efficient and less intrusive solution compared to traditional methods. [ABSTRACT FROM AUTHOR]

Geothermal energy is a key part of sustainable and renewable energy strategies, especially for clean heating in northern regions. This study focuses on Qihe County in Shandong Province, applying a controlled source audio-frequency magnetotellurics (CSAMT) method to investigate deep karst geothermal reservoirs. This research addresses the complex geological conditions and electromagnetic interference in the region, aiming to improve sustainable geothermal resource development. The findings indicate that the geothermal reservoir in the study area primarily consists of Ordovician limestone, characterized by moderate burial depth, high water volume, and elevated water temperature. Integrating CSAMT with vertical electrical sounding (VES) and radiometric surveying has clearly defined the deep aquifer layers and major water-controlling fault structures. Drilling verification results demonstrate the significant effectiveness of the integrated geophysical methods employed, providing reliable technical support for deep geothermal exploration in similar regions. This study makes a significant contribution to the scientific and technical foundation necessary for the sustainable development and utilization of geothermal resources, supporting the broader goals of environmental sustainability and renewable energy. [ABSTRACT FROM AUTHOR]

Abstract Yangshan gold belt (YSGB) in Gansu Province is a super‐large orogenic gold deposit located in the middle section of the Mianxian‐Lueyang arcuate suture zone (Mian‐Lue suture zone). The YSGB is mainly divided into the Gejiaowan, Anba, and Gaoloushan mine sections. The ore veins are strictly controlled by strong strain zones in the fracture zone and secondary fractures superimposed on the inherited activity and are vein‐like in general and lenticular in localities. For a long time, there have been different understandings regarding its ore‐controlling factors and mineral genesis. By utilizing controlled‐source audio‐frequency magnetotellurics (CSAMT) technology to conduct electrical characteristic studies, the deep electrical structural characteristics of the Gaoloushan section are identified, and a tectonically‐controlled geoelectric model of the deposit is established, which provides geophysical evidence for the view that the Yangshan gold mine is a tectonically‐controlled low‐temperature hydrothermal deposit in altered rock, guiding the arrangement of exploration work and identifying prospective mining areas, and thereby providing a geophysical exploration paradigm for deep exploration of large orogenic gold deposits.

Copyright of World Nuclear Geoscience is the property of World Nuclear Geoscience Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Controlled source audio‐frequency magnetotelluric is frequently used in association with other geophysical methods, especially in complex geological areas to highlight geological structures such as water reservoir rock. Although it gives satisfactory results, combining several methods requires time and expense. In addition, despite this combination, several drilling locations proposed after geophysical investigations were inaccurate, resulting in many unsuccessful drillings. The latter occurs due to the difficulty to emphasize the fracture zones properly. To work around this problem, we proposed a novel approach called pseudostratigraphic to reduce the repercussion of unsuccessful drilled boreholes and to demarcate the water reservoir rock. The technique consists to discretize the resistivity of the inverted OCCAM2D model based on the true layer resistivities collected from the borehole log data (observed layers). The discrete resistivity model is known as the new resistivity model. It is used to generate the pseudostratigraphic log at each station by pseudo‐demarcating the thicknesses of the observed layers with a low margin of error. Moreover, the combination of multiple new resistivity models from different survey lines creates a three‐dimensional pseudostratigraphic map useful to emphasize the water reservoir rock. The pseudostratigraphic implementation is carried out in the Xingning area as a real‐world case study. The results show that the intersection of the main fault (F1) and the conductive zones (≤100 Ω m) indicates the potential water reservoir rock. Its thickness is estimated around 150–600 with an error equal to ± 7°m. Based on the three‐dimensional pseudostratigraphic map, the water found in the fracture zone located under the reservoir rock is considered much hotter due to the intense geothermal activity along F1, thereby making it a better place for hot water exploitation. Finally, the pseudostratigraphic technique could be an innovative and cheap strategy to find groundwater reservoirs in complex geological areas. [ABSTRACT FROM AUTHOR]

Zhaoping fault in Jiaodong area is an important gold ore controlling fault. Many large, medium and small gold deposits have been identified nearby, and the controlled gold resources are nearly 2 000 t. The existing geological data show that Zhaoping fault is mainly developed in the fracture alteration zone near the contact zone between Qixia sequence granite and Linglong sequence granite. In recent years, with the increasing exploration depth, it is found that the occurrence of the deep part of the fault is different from that of the shallow part, and its spatial occurrence law needs to be further studied and verified. Therefore, the controllable source audio frequency magnetotelluric survey is carried out in the deep part of the typical Dayingezhuang and Jiaogezhuang deposits, and a three-dimensional physical property structural model was established to characterize the deep lateral subduction law of the fault zone by inversion resistivity parameters. The model shows that the Zhaoping fault zone corresponding to the gradient zone of resistivity changes extends downward in a gentle wave shape. It is inferred that its depth is more than 2 500 m, and the depth slows down and lies to the northeast. Combined with the ore control characteristics of the fault and a priori geological information, two deep prospecting targets are predicted at the change of fault occurrence, which are confirmed by drilling. On one hand, the geophysical evidence of the lateral lodging law of Zhaoping fault proposed in this paper improves the understanding of the fault zone, and has a certain guiding significance for the deep prospecting prediction and work deployment of the fault zone. On the other hand, this work verifies that it is feasible to use the CSAMT method to detect the deep gold ore-controlling structure in the fault zone. [ABSTRACT FROM AUTHOR]

Copyright of Geology & Resources is the property of Geology & Resources Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Controlled Source Audio-frequency Magnetotellurics (CSAMT) is a geophysical method utilizing artificial electromagnetic signal source to estimate subsurface resistivity structures. One-dimensional (1D) inversion modelling of CSAMT data is non-linear and the solution can be estimated by using global optimization algorithms. Particle Swarm Optimization (PSO) and Grey Wolf Optimizer (GWO) are well-known population-based algorithms having relatively simple mathematical formulation and implementation. Hybridization of PSO and GWO algorithms (called hybrid PSO-GWO) can improve the convergence capability to the global solution. This study applied the hybrid PSO-GWO algorithm for 1D CSAMT inversion modelling. Tests were conducted with synthetic CSAMT data associated with 3-layer, 4-layer and 5-layer earth models to determine the performance of the algorithm. The results show that the hybrid PSO-GWO algorithm has a good performance in obtaining the minimum misfit compared to the original PSO and GWO algorithms. The hybrid PSO-GWO algorithm was also applied to invert CSAMT field data for gold mineralization exploration in the Cibaliung area, Banten Province, Indonesia. The algorithm was able to reconstruct the resistivity model very well which is confirmed by the results from inversion of the data using standard 2D MT inversion software. The model also agrees well with the geological information of the study area.

Copyright of Rudarsko-Geolosko-Naftni Zbornik is the property of Faculty of Mining, Geology & Petroleum Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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.

Copyright of Coal Geology & Exploration is the property of Xian Research Institute of China Coal Research Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Underground goaves were left in many mining areas due to the continuous exploitation of coal resources. These mining areas seriously affect the production safety of the mines and the safety of life and property of the surrounding residents. Enormous safety hazards will be generated if the goaf range is not accurately controlled. In this study, we proposed a method for the detection of goaves in coal mines with a complex terrain by combining controlled source audio-frequency magnetotellurics (CSAMT) and an activated-carbon method for radon measurement. The disadvantage of failing to interpret goaf depth for the activated-carbon method for radon measurement was compensated by the advantage of the capability of goaf-depth sounding for CSAMT. Subsequently, the reference for CSAMT data was provided by the immunity of the activated-carbon method for radon measurement to the influences of terrain, earth electricity, and EMF. On this basis, the proposed method was employed to detect the goaf of Houjiagou Coal Mine in Liulin County, China, and obtained reliable detection results. The feasibility of the comprehensive geophysical prospecting method in the complex terrain was verified and it provides a new reference for the detection method of goaves with other conditions. [ABSTRACT FROM AUTHOR]

The recordings of controlled source audio electromagnetic (CSAMT) are invariably contaminated with powerline noise, which seriously impedes the application of CSAMT in densely populated areas. Based on the integer-period cancellation, a powerline noise suppression scheme is described for CSAMT data acquisition and processing. The essence of this scheme is to choose reasonable transmitting frequencies and window lengths of spectrum estimation. According to the specified power transmission standard, a set of CSAMT transmitting-receiving frequencies and sampling lengths can be designed. The effective amplitude and phase can be estimated through dividing the pre-filtered soundings into specified segments for spectrum estimation and Robust stacking. Without involving the magnetic field that is more sensitive to noise, the electric field component is directly converted into the full-field apparent resistivity directly to obtain geoelectric feature. Synthetic and field examples indicate that the nonstandard powerline noise can be effectively suppressed. This scheme can be easily embedded in most of the modern instrumentations, and extend application conditions to high cultural noise areas. • The transmitter frequencies and sampling lengths can be optimally designed. • Combination method based on integer-period cancellation can effectively remove noise. • This scheme can be easily embedded in most of the modern instrumentations. [ABSTRACT FROM AUTHOR]

At the stages of the FENICS experiment conducted in 2014 and 2019, unique data on deep electromagnetic sounding with grounded sections of industrial power lines were obtained at distances from 180 to 940 km from the center of the supply line to the measuring installation. The electromagnetic field components were recorded by VMTU-10 measuring equipment (VEGA, St. Petersburg). The fluctuations of the current in the supply line were recorded as a time series with a sampling rate of 1 kHz. Based on synchronous time series of the field components at the observation points and the current strength in the supply vibrator, estimates of the power spectra of the autocorrelation and cross-correlation functions of the recorded values were calculated using fast Fourier transform (FFT). The resulting spectral characteristics were used to determine the amplitudes of the field components of the source and phase shifts between them, as well as to estimate the impedance tensor components. To do this, correction factors were calculated for the ratio of the apparent resistivity values for the horizontal magnetic field component to those for the impedance and electric field. A 2D interpretation is made and estimates of the resistivity allocation at depth are obtained for two sublongitudinal and sublatitudinal profiles of the Karelia–Kola region. [ABSTRACT FROM AUTHOR]

Traditional controlled-source audio-frequency magnetotellurics (CSAMT) radiates symmetric beams using a grounded symmetric dipole (GSD). Only a tiny fraction of radiant energy is taken advantage of during the far-field (Ff) observation due to the low directivity of the GSD. In order to enhance the signal-to-noise ratio (SNR) during the Ff observation, it is necessary to reduce the transceiving distance (TD) or increase the transmitting power (TP), but both methods will cause many problems. Further, when using the tensor method for observation, GSDs in two vertical directions will be employed to radiate energy, and then a series of problems will occur such as an asymmetry of the SNR in two vertical directions if the geological conditions under the two GSDs vary widely. An arithmetic phase difference (APd) weighting asymmetric beamforming method (ABFM) in CSAMT is proposed in this paper, which uses a GSD array instead of a single GSD, and a signal with APd is transmitted to control the wavefront for beam steering. A significant enhancement (about 3 dB) of the SNR will occur by collecting the radiant energy in the region of concern (RoC) using ABFM. The analysis and simulation results demonstrate that under the premise of the same TD and TP, the ABFM has obvious advantages in improving energy utilization in CSAMT. In other words, the APd-weighted ABFM can deal with a complex noise environment in the field better than the traditional method. [ABSTRACT FROM AUTHOR]

The Ningdong mining area in the western Ordos Basin, China, mainly mines coal seam in Yan'an group, where its overlying rock is a thick sandstone layer of the Middle Jurassic Zhiluo Formation. This rock layer poses a direct water hazard threat to the coal mining if it is water-rich. The water abundant rock layer in the upper strata of Zhiluo Formation forms a low-resistivity overburden layer, decreasing the resolution of controlled source audio magnetotelluric (CSAMT) method in detecting water-bearing in the lower part of Zhiluo Formation sandstone layer of coal seam direct roof. Therefore, under the influence of the low resistivity overburden of the upper sandstone, how to accurately detect the aquosity of the lower sandstone layer is of great importance to the safe mining of coal mines in the region. On the basis of CSAMT detection, combined with high-resolution seismic exploration method, the joint inversion of seismic and CSAMT is realized by using cross-gradient operation between the seismic wave impedance attributes clustered by particle swarm algorithm and CSAMT inversion model. The seismic data fitting term in the joint inversion objective function is discarded, and the pseudo-2D inversion method is used for CSAMT to reduce the calculation cost of the inversion. A 3D geological model conforming to the hydrogeological characteristics of the Ningdong mining area is established, and the joint inversion test between seismic and CSAMT is conducted, proving the feasibility and applicability of joint inversion to detect the water enrichment of sandstone in this area. The accuracy of the seismic and CSAMT joint inversion results is verified by combining the engineering example of water abundance detection in the sandstone layer in Maiduoshan coal mine that accorded with the typical hydrogeological characteristics of Ningdong mining area and the results of later downhole drilling exposures, which is remarkably better than the single method. The research shows that the joint inversion of seismic and CSAMT can accurately identify the water abundance of the lower sandstone layer and its range under the influence of the upper low resistance sandstone overburden and achieve the purpose of fine detection of the water abundances of the lower sandstone layer of the Zhiluo Formation. The joint inversion can provide important safety geological guarantee for the mining of coal seams in the Ningdong mining area in the western part of Ordos Basin. [ABSTRACT FROM AUTHOR]

Vector controlled-source audio-frequency magnetotellurics (CSAMT) emits electromagnetic waves with a low directivity coefficient using a grounded horizontal electric dipole (HED). During observations in the far-field region (FfR), only a fraction of radiation energy is used. To improve the signal-to-noise ratio (SNR) in the FfR, it is necessary to increase the power of the transmitter or shorten the transceiver distance, but it will restrict the development of vector CSAMT. Comparatively, the tensor CSAMT uses HEDs in two directions to measure geological bodies in every direction. If the geological conditions of two HEDs are vastly different, it is easy to cause issues, such as an imbalance of the SNR in two directions of the receiving point. This paper presents a comparative study of a novel arithmetic amplitude-phase (AAP) weighted beamforming method (BFM) in vector and tensor CSAMT, which uses multiple HEDs to transmit signals with controlled amplitude ratio and phase difference to modulate the wavefront, thereby achieving beam steering and other additional functions (such as amplitude compensation). By concentrating the radiation energy in the area of interest (AoI) using BFM, the SNR can be largely regulated. The comparative simulation and analysis demonstrate that the BFM has advantages in improving energy utilization and beam steering in vector and tensor CSAMT. On the premise of same power and transceiver distance, using the AAP-weighted BFM, the SNR received in the AoI can meet the requirements better than that received via the traditional method. [ABSTRACT FROM AUTHOR]

In traditional controlled-source audio-frequency magnetotellurics (CSAMT), the orthogonal magnetic and electric field components in the far-field region are recorded to calculate the apparent resistivity. However, as the distance between the receiver and the transmitter increases, the electromagnetic signal weakens considerably. Moreover, as the location of the transmitter is fixed, the location of the far-field region also is fixed, which limits the exploration range. In this study, a novel phased-array transmitting source was proposed to overcome this limitation. In traditional CSAMT, a grounded single-dipole long-line source is used to transmit the electromagnetic wave. This source has a low gain and no directionality, resulting in a low signal-to-noise ratio (SNR) in the area of interest (AoI). Conversely, by using a phased-array source, beam control and stable directional radiation will be achieved so that the electromagnetic energy should be capable of effectively focusing within the AoI. Without increasing the transmitting power, the SNR should be conveniently enhanced and the size of the AoI can be greatly increased. In this paper, the characteristics of the radiation field of a single-dipole long-line source and its application in traditional CSAMT are analyzed. The design principle and the method of implementation of a novel phased-array source are provided. The feasibility and effectiveness of the proposed source are verified by simulations and experiments, and a prototype is realized. [ABSTRACT FROM AUTHOR]

Controlled-source audio-frequency magnetotellurics (CSAMT) is an important geophysical tool which has been widely used in many areas, such as mineral surveys and groundwater and geothermal exploration. Numerous studies have shown that resistivity anisotropy has a significant influence on CSAMT responses, while another important physical parameter—magnetic susceptibility—is often neglected. In fact, for items such as magnetic minerals, steel pipes and concrete reinforcing bars, the magnetic susceptibility is often non-negligible. However, to the best of our knowledge, there are no three-dimensional (3D) CSAMT studies that have taken both resistivity anisotropy and magnetic susceptibility anisotropy into consideration. Therefore, we present a 3D CSAMT forward modeling algorithm which is capable of handling 3D resistivity and susceptibility anisotropic anomalies using the finite element method. In the far-field zone, this algorithm shows highly accurate results by comparison with the analytical and numerical solutions of MT. Then, the responses of four different models are studied. The results show that for magnetic anomalies with low resistivity contrast, the consideration of magnetic susceptibility is essential, as high susceptibility may seriously distort or even invert its responses. [ABSTRACT FROM AUTHOR]

The subsidence or collapse of coal mine goaf has a great impact on the construction of various large-scale projects and the environment, and can threaten the safety of people's lives. In the present study, CSAMT was used to detect coal mine goaf in China's Fangzi mine. Anti-interference data acquisition and processing strategies were adopted to enhance and classify electrical characteristics to improve goaf detection accuracy under strong interference. Experiments were first performed under strong interference, based on the geological and geophysical goaf characteristics. To acquire high-precision CSAMT data, the effects of emission parameters, electromagnetic high-voltage interference, and other factors were investigated. Data were postprocessed using multilevel low-pass filtering approaches, including static correction, threshold segmentation, and the power function method, to reduce data noise, remove shallow abnormal interferences, and enhance the abnormal electrical characteristics of deep goaf. Finally, k-means clustering was used to categorize CSAMT electrical characteristics and quantitatively analyze the resistivity values. Results showed that the proposed method performs effectively for the identification of coal mine goaf. [ABSTRACT FROM AUTHOR]

Controlled source audio magnetotelluric (CSAMT) has good depth penetration and high data quality. However, the Cagniard apparent resistivity calculated in the near- field zone and transition zone is distorted, and collecting electric field components in some specific landscapes requires a high cost, such as desert, permafrost, and water areas. The magnetic field y-component (Hy) is not restricted by bad electrode grounding conditions, and the signal level is greater than that of the magnetic field z-component (Hz), which can be used to obtain the ground resistivity. A simple algorithm was used to calculate the apparent resistivity defined by Hy, and the response characteristics and measurement range were analysed by model calculation. The results show that the Hy full-field apparent resistivity has no obvious distortion. This method is applied to geological surveys in the Xiong'an New Area, China. The results indicate that the detection depth of the Hy full-field apparent resistivity is better than that of electric field x-component (Ex), and the signal-to-noise ratio is better than that of Hz. Moreover, the 1D and 2D inversion results are in good agreement with the known geological conditions. This method can extend the observational conditions and range of CSAMT. [ABSTRACT FROM AUTHOR]

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of the Chinese Society of Rare Earths is the property of Editorial Department of Journal of the Chinese Society of Rare Earths and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The detection of the depth and temperature of deep geothermal reservoirs suffers great uncertainty if it is completed using the simple combination of traditional geophysical and geochemical methods. Given this, this study investigated the combined utilization of multiple methods including the multi-information joint detection using the controlled source audio frequency magnetotellurics (CSAMT) method and geothermometers in the Qutan geothermal field. First, the reservoir temperature and the depth of geothermal water circulation in the geothermal field were estimated using the geochemical method. Afterward, the relationship between the CSAMT resistivity and temperature of strata was explored through borehole temperature measurement. Based on this, the depth and temperature of geothermal reservoirs in the geothermal field were estimated again. According to the comprehensive analysis and comparison of the thermal reservoir temperatures and depths obtained using the two methods, the shallow reservoirs in the Qutan geothermal field have a top burial depth of approximately 423 m, a thickness of about 300 m, a temperature of about 79°C, and a fluid circulation depth of about 1959 m.

Underground goaves were left in many mining areas due to the continuous exploitation of coal resources. These mining areas seriously affect the production safety of the mines and the safety of life and property of the surrounding residents. Enormous safety hazards will be generated if the goaf range is not accurately controlled. In this study, we proposed a method for the detection of goaves in coal mines with a complex terrain by combining controlled source audio-frequency magnetotellurics (CSAMT) and an activated-carbon method for radon measurement. The disadvantage of failing to interpret goaf depth for the activated-carbon method for radon measurement was compensated by the advantage of the capability of goaf-depth sounding for CSAMT. Subsequently, the reference for CSAMT data was provided by the immunity of the activated-carbon method for radon measurement to the influences of terrain, earth electricity, and EMF. On this basis, the proposed method was employed to detect the goaf of Houjiagou Coal Mine in Liulin County, China, and obtained reliable detection results. The feasibility of the comprehensive geophysical prospecting method in the complex terrain was verified and it provides a new reference for the detection method of goaves with other conditions.

Shallow conductive heterogeneity can lead to static shifts ain the apparent resistivity sounding curve of controlled-source audio-frequency magnetotellurics (CSAMT). The static effect will shift the apparent resistivity curves along with axial log-log coordinates. Such an effect, if not properly processed, can distort the resistivity of rock formation and the depth of interfaces, and even make the geological structures unrecognizable. In this paper, we discuss the reasons and characteristics of the static shift and summarize the previous studies regarding static shift correction. Then, we propose the Guided Image Filtering algorithm to suppress static shifts in CSAMT. In detail, we use the multi-window superposition method to superimpose 1D signals into a 2D matrix image, which is subsequently processed with Guided Image Filtering. In the synthetic model study and field examples, the Guided Image Filtering algorithm has effectively corrected and suppressed static shifts, and finally improved the precision of data interpretation.

The apparent resistivity tensor ρB is an electromagnetic transfer function, which can be used to analyze and explain the underground electrical structure. Conventional method for obtaining the parameter requires controlled sources and can be easy to be disturbed by cultural noises. We present a new method for calculating the apparent resistivity tensor, the current density is first obtained by measuring the curl operator of the magnetic field on the Earth's surface. This approach is independent of the assumption of a plane wave, and may be used irrespective of source types and field areas. We derived the analytical expressions of the apparent resistivity tensor based on synthetic horizontally layered models with a vertical magnetic dipole source. We then calculate the responses of ρB through numerical modeling examples using both natural sources and controlled sources. Compared to traditional apparent resistivity definitions, our apparent resistivity tensor has the same amplitude value but with more sensitive phases in the far zone, and shows few distortions in the transition zone. And in the near-field zone, it is closer to the resistivity distribution under the ground. The simulation results have demonstrated the effectiveness of the proposed method for calculating the apparent resistivity tensor. [ABSTRACT FROM AUTHOR]

Abstract On June 29, 2015, a small phreatic eruption occurred in the most intensively steaming area of Hakone volcano, Japan. A previous magnetotelluric survey for the whole volcano revealed that the eruption center area (ECA) was located near the apex of a bell-shaped conductive body (resistivity

We have developed a three-dimensional (3-D) algorithm for computing the controlled-source audio-frequency magnetotelluric response which is capable of handling local inhomogeneities in the electrical conductivity and magnetic permeability distribution. It is a difference equation algorithm that is based on the integral forms of Maxwell's equations. To avoid a spatial singularity being introduced by the source, we used a secondary electric field approach. We adopt a staggered-grid finite difference method to disperse the secondary electric field equation which is simple to realize and can calculate relatively complex models. The final sparse equation system after dispersion is solved using an ILU preconditioning quasi-minimal residual (QMR) method. The code is validated for nonmagnetic and permeable conductive structures by two synthetic models. One of them is a two-dimensional (2-D) nonmagnetic conductive geoelectric model; we validate our 3-D computation result by comparing it to the result of 2-D CSEM finite element forward program. The other one is a 3-D permeable geoelectric model; we validate our 3-D computation result by using the COMSOL Multiphysics software. We also designed two theoretical 3-D geoelectrical models to analyze the effects of magnetic permeability heterogeneity. Numerical simulation results well reveal the influence of magnetic permeability heterogeneity on high-resistance and low-resistance models. [ABSTRACT FROM AUTHOR]

In order to accurately identify the old goaf in Pingshuo mining area, based on the optimized electrical exploration method, a parameter optimization test was performed to determine the corresponding construction technology system, and it was applied on site. The results show that the electrical exploration in Pingshuo mining area was mainly based on the TEM to detect the goaf and water accumulation area, the CSAMT was used to detect the middle and deep and multi-layer goaf, and the DC method was used to detect the strong electromagnetic interference and shallow mined-out area of the pit step area. After parameter optimization, the TEM wire frame was 240 m × 240 m, the frequency was 8 Hz, the power supply current was 10 A, the CSAMT transmission and reception distance was 3.5 km, the MN point distance was 10 m, and the measurement point distance was 2～5 m, the influence of different AO distances in DC method was small. The research conclusions preliminarily determined that the TEM and the CSAMT were suitable for the detection of the goaf in the Pingshuo mining area, and the construction parameters provided a more reliable reference for the precise exploration of the goaf in the Pingshuo mining area. [ABSTRACT FROM AUTHOR]

Copyright of Nonferrous Metals (Mining Section) is the property of Beijing Research Institute of Mining & Metallurgy Technology Group and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Carbon-bearing stratum normally features low resistance and high polarization. If the lithostratigraphy of the exploration area contains large amounts of carbon, the induced polarization anomaly caused by metal sulfide ore bodies will be inundated by the high polarization of carbon-containing wall rock. In this work, we adopted time-domain induced polarization (TDIP) and controlled-source audio-frequency magnetotellurics (CSAMT) on deep prospecting of the carbon-bearing stratum of the Ar Horqin Banner, Inner Mongolia. The underground medium is divided into target geologic bodies according to the geological information within the known exploration line borehole, and the physical properties of various target geologic bodies are calculated using weighted averages to build a geologic–geophysical model that can fit the observation data. Consequently, we can determine the range and morphological characteristics of the electrical properties of the ore-bearing geologic bodies in the inversion results in the study area. Then we can use the characteristics summarized from the known exploration line to interpret unknown exploration line. Results indicated that, when the difference in physical properties between the ore body and interference wall rock is not clear, the geologic body can be classified via the paragenetic (associated) assemblage relations of the underground medium. Geological interpretation is guided by the comprehensive physical properties of ore-bearing geologic bodies to avoid interferences. [ABSTRACT FROM AUTHOR]

The Southwestern area of Fujian Province in China contains a major metallogenic belt. There have been three major tectonic movements since the Late Paleozoic, and the thrusts here are the main mineral deposits. These occurred between the Early Carboniferous and Late Permian eras. Due to dramatic undulations in the surface and associated complex underground structures, a single geophysical method cannot provide reliable imaging results. This is largely due to difficulties in data acquisition and processing. Seismic exploration provides one example. Using this method, raw shot gathers have a low signal-to-noise ratio because of the undulations in the topography. Furthermore, strong lateral velocity variation makes the migration process exceedingly difficult. This means that interpretations of the resulting reflection seismic profile give rise to uncertainty. For this reason, two-dimensional reflection seismology and controlled source audio-frequency magnetotellurics (CSAMT) electromagnetic sounding techniques were performed. After initially completing conventional processing on the seismic reflection data, subsequent pre-stack depth migration (PSDM) over the rugged topography yielded a much better image. It was able to identify thrust faults and magma intrusions. Then, using CSAMT, inversion was conducted with the same topography as the seismic reflection. By combining the migrated seismic profile, inverted resistivity profile, and borehole data, a vertical geological model was constructed. This proved the existence of an overlapped thrust, and it also indicated the possible presence of deeper mineralization. [ABSTRACT FROM AUTHOR]

Banded thermal reservoirs are important geothermal resources in coastal areas of China. Deep geophysical technology is the main tool used to explore the formation and accurately identify the fracture system and thermal storage structure. Jianghai industrial park in Jiangsu Qidong is in the coastal beach reclamation district. A thick layer of saltwater with a salinity of 20 g/L from the surface to a depth of 200 m forms an ultra-low resistance shielding layer in that area. We use controlled source audio-frequency magnetotelluric (CSAMT) soundings to explore this area using a one-dimensional inversion technique to overcome the effect of the transition zone and increase the effective depth of our exploration. Simultaneously, we encrypt the line to screen out false anomalies caused by the static effect and multiple solutions. Combining with the existing geological data, this methodology allows the identification of heat storage in the low-resistance layer strip. Using CSAMT for exploration provides the basis of developing and utilizing both geothermal resources along the coastal shoal reclamation district and the ultra-low resistance shielding layer for banded thermal storage. [ABSTRACT FROM AUTHOR]

We propose a new 3D inversion scheme to invert the near- and transition-zone data of CSAMT with topography accurately. In this new method, the earth was discretized into unstructured tetrahedra to fit the ragged topography and the vector finite-element method was adopted to obtain precise responses and good sensitivity. To simulate the attitude and shape of the transmitter, we divided a long-grounded transmitter into dipoles and integrated these dipoles to obtain good responses in the near- and transition-field zones. Next, we designed an L2 norm-based objective functional and applied a standard quasi-Newton method as the optimization method to solve the inverse problem and guarantee steady convergence. We tested our 3D inversion method first on synthetic data and then on a field dataset acquired from select sites near Changbai Mountain, China. In both tests, the new inversion algorithm achieved excellent fitting between the predicted and observed data, even in near- and transition-field zones, and the inversion results agreed well with the true model. These findings reveal that the proposed algorithm is effective for 3D inversion of CSAMT data. [ABSTRACT FROM AUTHOR]

This paper aims to study the deep electrical conductivity of the Murmansk block (Fennoscandian Shield) using the controlled source audio-frequency magnetotelluric (CSAMT) and audiomagnetotelluric (AMT) methods. One of the most important tasks in deep sounding studies implying the joint application of the AMT and CSAMT methods is to take into account the influence of surface conductors on the measurement results (static shift). To solve this problem, we develop a methodology for processing and interpreting the measurement data of the CSAMT and AMT system using the results of the deep sounding experiment conducted in the frequency range from 1 to 500 Hz performed in 2018 (Murman-2018) as an example. Measurements with the controlled source in the form of two mutually orthogonal horizontal electric dipoles are taken at distances of 12 to 105 km. The generator-measuring complex consisted of the VMTU-10 measuring station (manufactured by OOO VEGA, St. Petersburg) and the Energy-4 generator (developed at the Kola Science Center, Russian Academy of Sciences, Apatity). Using the synchronous time series of the field components at the observation points and the current in the supply dipole, the power spectra of the autocorrelation and cross-correlation functions of the recorded values are calculated based on the fast Fourier transform (FFT). The obtained spectral characteristics are used (i) to determine the amplitudes of the source field's components and the phase shifts between them, and (ii) to evaluate the components of the AMT field's impedance tensor. The values of the apparent resistivity are calculated using the amplitudes of the horizontal components of the electromagnetic field and the impedance ratios. The obtained measurement results are corrected for the static shift. For this, the correction coefficients are calculated from the ratio between the apparent resistivity values for the horizontal component of the magnetic field and the apparent resistivity values inferred from the impedance and electrical field values. The data for the cases of axial and equatorial arrays, together with the data of the AMT and remote sounding, made it possible to establish a high degree of lateral homogeneity of the deep electrical section and to expand the frequency range of the obtained curves of the apparent resistivity and impedance phase. A one-dimensional interpretation is made to obtain estimates of the distribution of the deep resistivity. [ABSTRACT FROM AUTHOR]

CSAMT or Controlled Source Audio-Magnetotelluric is one of the Geophysics methods to determine the resistivity of rock under earth surface. CSAMT method utilizes artificial stream and injected into the ground, the frequency of artificial sources ranging from 0.1 Hz to 10 kHz, CSAMT data source effect correction is inverted. From the inversion results showed that there is a layer having resistivity values ranged between 2.5 Ω.m – 15 Ω.m, which is interpreted that the layer is clay.

This paper presents a novel numerical method for simulation controlled-source audio-magnetotellurics (CSAMT) and radio-magnetotellurics (CSRMT) data. These methods are widely used in mineral exploration. Interpretation of the CSAMT and CSRMT data collected over an area with the complex geology requires application of effective methods of numerical modeling capable to represent the geoelectrical model of a deposit well. In this paper, we considered an approach to 3D electromagnetic (EM) modeling based on new types of preconditioned iterative solvers for finite-difference (FD) EM simulation. The first preconditioner used fast direct inversion of the layered Earth FD matrix (Green's function preconditioner). The other combined the first with a contraction operator transformation. To illustrate the effectiveness of the developed numerical modeling methods, a 3D resistivity model of Aleksandrovka study area in Kaluga Region, Russia, was prepared based on drilling data, AMT, and a detailed CSRMT survey. We conducted parallel EM simulation of the full CSRMT survey. Our results indicated that the developed methods can be effectively used for modeling EM responses over a realistic complex geoelectrical model for a controlled source EM survey with hundreds of receiver stations. The contraction-operator preconditioner outperformed the Green's function preconditioner by factor of 7-10, both with respect to run-time and iteration count, and even more at higher frequencies. [ABSTRACT FROM AUTHOR]