Ji'nan possesses highly abundant geothermal resources, which are hosted by Ordovician-Cambrian karst-fissured geothermal reservoirs and Neogene-Paleogene clastic pore-fissure geothermal reservoirs. The geothermal exploration in this study focuses on the Ordovician-Cambrian karst fissured geothermal reservoirs in Daqiao Town in northern Ji'nan. Through geophysical profile measurements, this study aims to identify the distributions of strata and fault structures and the burial depths of geothermal reservoirs, infer the attitudes and spatial morphologies of fault structures associated with heat control and conduction, delineate the target area for geothermal well construction, and conduct drilling verification in the favorable underground water-rich position. Building on the collected data, this study interpreted and inferred the fault structures in the study area and comparatively analyzed the water-bearing properties by employing direct-current sounding, controlled source audio magnetotellurics, and magnetotelluric survey. A geothermal exploration and production combined well was constructed in a favorable position of the geothermal target area, manifesting a completion depth of 1 532.06 m, a static-water burial depth of 13.03 m, a wellhead water temperature of 50.1 ℃, a water yield of 132.998 m³/h, and a dropdown depth of 18.27 m.

Following China's planning for ore prospecting in overburden areas, China's geochemical exploration researchers have conducted extensive research on the fundamental theories, methods, and technologies of geochemical exploration for overburden areas in the past decade. They achieved significant advances mainly in two aspects: (1) the research on the migration mechanism, occurrence state, and anomaly formation mechanism of elements in overburden areas; (2) advances in methods and technologies, including geoelectrochemistry, active state of elements, geogas, separation of micro-fine-sized soil particles, soil thermomagnetic composition, and integrated gas survey, as well as numerous experimental demonstrations. These advances represent continuous progress in the research on the fundamental theories, methods, and technologies of geochemical exploration for overburden areas, providing new geochemical methods and technologies for ore prospecting breakthroughs in overburden areas.

The Laiwu area in central Shandong Province, situated in the eastern North China Craton, is a significant production area of skarn iron-rich ores. Its ore deposits occur primarily in the contact zone between the mining rock mass and the Middle Ordovician carbonate formation. Based on the latest areal gravity and magnetic survey results, this study thoroughly investigated the characteristics of gravity and magnetic anomalies along the Shijiaquan-Liujiamiao area in the western periphery of the mine rock mass. Then, this study delineated the deep prospecting target combining the characteristics of gravity and magnetic fields of the known iron deposits in the Laiwu area. Large-scale gravity and magnetic profiles were arranged in the favorable mineralization area. With the known boreholes as constraints, the gravity and magnetic anomalies were qualitatively and quantitatively interpreted using the 2.5D gravity-magnetic joint inversion technique. The interpretation results provide a basis for the location and depth of the borehole to be placed, which revealed a 15.8 m-thick iron-rich ore deposit, suggesting remarkable prospecting effects. This study holds critical indicative significance for further exploration of skarn iron ore deposits in this area.

The artificial source electromagnetic method is an important technique for deep resource exploration. The key challenge is to improve the depth and precision of detection through innovative technology. The detection mode of electromagnetic methods is evolving from far-field to near-field, and the study of near-source electromagnetic methods has become an international research frontier in recent years. Building on the recent advancements in wide-field electromagnetic methods and multi-channel transient electromagnetic methods, the short-offset transient electromagnetic method (SOTEM) has been further developed and proposed. The distinguishing features of SOTEM are its stronger signals and wider bandwidth, which are advantageous for achieving the detection requirements of greater depth and higher precision. This special issue presents eight articles covering the methods, techniques, software, and applications of SOTEM, providing strong support for the growing need for high-resolution subsurface detection.

Despite abundant geothermal reserves of the Tangyu geothermal field in Meixian County, Shaanxi Province, long-term exploitation has decreased the water temperatures and yields of its existing geothermal wells year by year. Hence, there is an urgent need to explore new potential geothermal resources in the geothermal field. Since the known geothermal wells in the geothermal field are significantly controlled by faults, investigating the deep fault propagation holds critical significance for exploring the geothermal field’s potential geothermal resources. Due to the method limitations and the topographic influence, identifying thermal control faults through conventional geological route investigation or large-scale engineering is not applicable to the geothermal field. Therefore, a new technical method combining the penetrating soil radon measurement and the controlled source audio magnetotelluric (CSAMT) method was employed in this study to find concealed faults and delineate potential geothermal areas. Based on the measured surface soil radon concentration anomaly data and the subsurface electrical structure model derived from the CSAMT data inversion, this study inferred six new concealed faults on the basis of corroborating the known faults, predicted two potential geothermal areas, and built a conceptual model for the Tangyu geothermal field. As revealed by the results, the soil radon concentrations at concealed faults are much higher than the regional background value, and the concealed faults are located in the low-resistivity fracture zones as indicated by the apparent resistivity results based on CSAMT data inversion. Besides, the two potential geothermal areas spread from 450~750 m and 850~1 150 m on the profile, respectively, at depths of approximately 250~300 m. This study concludes that the geothermal field resides in a low-resistivity region with soil radon anomalies three times the regional background value. The results of this study provide a reference for the subsequent sustainable production and utilization of potential geothermal resources in the region.

Geothermal resources are significant clean energy and tourism mineral resources. The Rucheng Basin, a carbonate basin in the southeastern mountainous area of Hunan Province, possesses favorable conditions for the formation of convective geothermal energy. However, the basin is enclosed on three sides by the giant Zhuguangshan rock mass, and its basement is subjected to the intrusion and destruction by the rock mass, resulting in severely deformed formations, crisscrossing faults, and significantly different eastern and western structures. The understanding of the basin's water- and heat-conducting pathways and deep reservoir structures remains elusive, thus restricting the investigation of the basin's geothermal potential. Hence, this study probed the basin's deep structures through gravity survey and audio magnetotellurics (AMT), obtaining the following insights: (1) The Rucheng Basin has developed into a bidirectional ramp structure due to east-west differentiation. The synclinorium in the east experienced compression and clockwise rotation due to the emplacement of the Yanshanian rock mass, rocks were fragmented in the core zone, and strike-slip fracture zones were found at the boundary. The faults have vertical cutting depths exceeding 4 km, widths ranging from 300~600 m, and dip angles between 80°~90°. (2) The basin's basement anticlinal axis hosts several NWW-directed concealed rock masses, with diameters from 3~4 km and buried depths from 0.5~1.5 km. Hot springs reside in the fracture zones crossing the boundaries of the concealed rock masses. (3) The basin boasts favorable conditions for the formation of convective geothermal energy. Folds, fault zones, and concealed rock masses match each other to form a unified spatial combination of heat-controlling elements, manifesting heat accumulation characterized by east-west recharge and intermediate discharge. With more thriving deep geothermal reservoirs in the east, the basin has high potential for geothermal resources.

The Fengtai ore concentration area is an important producing area of plumbum-zinc and gold ores in the middle of the Qinling orogenic belt. It hosts many large to super-large deposits, such as Qiandongshan-Dongtangzi, Bafangshan-Erlihe, Baguamiao, and Shuangwang deposits. With the exploitation proceeding, the reserves of these deposits have decreased significantly, and the ore prospecting in these deposits has shifted from the surface to the deep part. However, the geophysical fields in the deposits are yet to be ascertained, severely restricting research on the metallogenic regularity of the deposits and the ore prospecting and exploration in the peripheral zones. Based on the latest 1∶50,000 aeromagnetic and airborne radioactivity survey data, as well as gravity data, this study investigated the multi-source geophysical fields on the scales of the region, the ore concentration area, and deposits, aiming to summarize the distribution patterns of geophysical anomalies of different scales and provide evidence for research on metallogenic regularity and prospecting prediction. The results show that the Fengtai and the Xicheng ore concentration areas, with similar magnetic structures, are separated by the zone with strong magnetic anomalies caused by the crystalline basement of the Huicheng Basin. The first vertical derivative of gravity reveals that the Fengtai and Xicheng ore concentration areas have density structures similar to the Huicheng Basin. It can be inferred that the shallow part is a unified basin and that a large prospecting space exists between the two ore concentration areas. Many NW-trending linear magnetic anomaly zones occur in the Fengtai ore concentration area. Their locations are highly consistent with those of fault structures, and they were offset by NE-trending structures due to late transformation. The second vertical derivative of gravity reveals that many intermediate-acid intrusive stocks or veins have developed in the deep part of the Fengtai ore concentration area. Structural boundaries can be effectively identified based on the first vertical derivative, X-directional derivative, and wavelet transform of aeromagnetic data. Furthermore, ore bodies are mostly distributed in the NW direction along the tectonic belt. All these will play an important role in guiding ore prospecting and exploration in the Fengtai ore concentration area.

The eastern Kunlun metallogenic belt, as a significant metal metallogenic belt in China, hosts extensive orogenic gold deposits and large-scale Kunlunhe, Gouli, and Wulonggou gold concentration areas. The Dachaigou gold deposit is a large-scale gold deposit newly discovered in the Wulonggou gold field in recent years. Despite its high metallogenic potential, the western extension of its ore belt has not been defined. Hence, this study conducted induced polarization (IP) sounding and wide-field electromagnetic sounding in the deposit. The results show that the known ore belt is situated in the regional gravity anomaly gradient zone, the transition zone of positive and negative weak magnetic anomalies, the edge of IP anomalies, or the electrical gradient zone. The development zone of the regional tectonic belt resides in the large-scale IP anomaly section. The regional tectonic belt is characterized by a wide range of low-resistivity anomaly zones. The IV and III alteration zones of the known ore belt are located in the opening position of the low-resistivity anomaly zone and the shallow electrical anomaly gradient zone, respectively. Based on the above understanding and the electromagnetic anomaly change patterns of several parallel profiles in the western extension segment, it was inferred that the regional ore-controlling structure extends steadily in the W-NWW direction, forming a favorable prospecting space in the western extension segment of the deposit. The results of deep geophysical exploration in the Dachaigou deposit indicate that geophysical methods manifest significant advantages in deep geological prospecting research, providing successful experience for deep prospecting in the eastern Kunlun gold deposit area.

With the rapid development of urban infrastructure,the demand for urban geological work is increasing,and urban geological surveys become particularly important.Urban geophysical exploration has different exploration purposes and working environments from conventional geophysical exploration.Accordingly,compared with conventional geophysical exploration methods,the geophysical exploration methods for urban geological surveys face the challenges of many interference factors,limited construction sites and time,and high requirements for exploration accuracy.The opposing-coils transient electromagnetic(OCTEM) method enjoys a strong anti-interference ability,convenient and efficient construction,and high resolution.Therefore,this study employed the OCTEM method to investigate the test profile in the urban geological survey and evaluation of Haidong City.This test profile was subjected to numerous interference sources since it crossed 11 highways and railways and passed through factories,schools,logistics parks,villages,living quarters,and rivers.Consequently,the OCTEM results agree well with the results of single-point resistivity sounding and drilling results.Therefore,the OCTEM method proposed in this study is effective for urban geological surveys.

As a kind of clean energy, geothermal energy has attracted the attention of scholars all over the world in recent years. Previous geochemical exploration methods for geothermal resources are limited to the analysis of individual geochemical indices. Moreover, previous studies of microorganisms in geothermal fields mostly focus on hot spring outcrops, lacking ecological studies of geothermal resources in complex terrains. This study investigated the soil geochemistry and microbial diversity of the Bantang Hot Spring geothermal field in Chaohu, Anhui Province. Geochemical indices such as head-space gas, soil gas, acid-hydrolyzed hydrocarbons, and altered carbonate were detected in this study. Combined with the microbial high-throughput sequencing technology, this study analyzed the composition and spatial-temporal distribution of the microbial population above the geothermal fields in uplifted mountains and the relationship between these bioinformatics characteristics and the geochemical indices. The results indicate that the acid-hydrolyzed hydrocarbons on the surface of the geothermal field showed a maximum methane concentration of 43.7 μL/kg in the area between faults F2 and F3, adequately reflecting the fault location of the geothermal field.Bacillaceae, Hydrogenophilaceae, and Thermodesulfovibrionaceae in the geothermal field and the background area showed large relative abundance differences, which were 0.178%, 0.108%, and 0.060%, respectively. This result indicates that they are sensitive to geothermal resources and correspond well to geochemical indices above the known geothermal field. This study preliminarily investigated the diversity of geothermal microorganisms in the geothermal field and analyzed the corresponding relationships between microbial distribution characteristics and geochemical indexes, providing technical support for the microbiological exploration of geothermal resources.

Distributed acoustic sensing (DAS) technology, one of the most advanced sound field detection technologies, can achieve distributed, long-distance, and high-precision real-time detection of the ambient vibration and sound field information interacting with optical fiber. The optical fiber exploration system of the DAS technology solves the problems of high cost and deployment difficulty of conventional geophones in complex geological environments. In recent years, the DAS technology has experienced rapid development, especially in monitoring application scenarios that require long-term and large-scale deployment. However, its systematic understanding is insufficient due to divergent research results. To further understand the research advances of the DAS technology in geophysical exploration for more effective subsequent research, this study systematically classified and summarized the development history of the DAS technology and its recent research results in geophysical exploration based on the oil and gas, marine, and environmental engineering application scenarios through literature research. This study focused on the development process of the DAS technology in different directions, the research advances in data processing, and relevant literature with specific results. Finally, this study generalized the development trend and urgent problems of the DAS acquisition system, analyzing the DAS development prospect.

Since the periphery of the Xishan rare earth deposit in Weishan County, western Shandong is mostly covered by the Quaternary strata, single geophysical exploration methods are ineffective in searching for rare earth elements in this area. To establish a geological-geophysical prospecting model for deep rare earth prospecting in this area, a combination of exploration techniques and methods suitable for the deep exploration of rare earth deposits in this area were selected through multiple geophysical exploration technology experiments on the known geological profiles. The distribution range of the underground Mesozoic Xishan alkaline complex was roughly determined through gravity survey and high-precision magnetic survey. The ore body outcrop was delineated through ground-based gamma spectrometry, and the deep ore body characteristics were revealed through drilling. Finally, this study developed an integrated geophysical exploration method including gravity-magnetic joint delineation of rock masses, radioactive positioning for ore body outcrops, and deep drilling. By using this exploration model, one super-large rare earth deposit was discovered in this area, providing a reference for the exploration of rare earth deposits in the surrounding area.

To improve the detection level of municipal roads for rapid and effective municipal road collapse warning and rapid search for municipal pipe network distribution, the 22^nd Research Institute of China Electronics Technology Group Corporation designed and developed real-time three-dimensional ground-penetrating radar (3D GPR). With the real-time 3D GPR, which is based on the architecture of field programmable gate array and digital signal processor (FPGA&DSP), the institute achieved the design and implementation of several key technologies for the multi-channel high-speed acquisition system, enriching the road detection techniques and methods. The real-time 3D GPR enables high-speed acquisition of ten-channel radar data using the horizontally polarized antennae equipped with five transmitters and six receivers. The channels can be switched using high-speed switches, which operate in an interactive interpolation manner. The 3D GPR allows for up to 32 channels and detection speeds of above 60 km/h (channel interval: 2 cm). This is attributed to the switching of the antenna array using switches. The optimum antenna polarization design was verified by the comparison of experimental data from cavity- and metal-plate-based experimental sites. As a result, the optimal antenna scheme was determined. The measured results show that, compared to general LTD-2600 radar, the real-time 3D GPR boasts a higher acquisition speed and higher performance in terms of amplitude and phase, conducive to the improvement of road disaster detection technologies. Therefore, there is high market demand for the real-time 3D GPR.

It is difficult to explore the overlapping double-layer waterlogged goafs using the transient electromagnetic method. The reason is that upper waterlogged goafs will hinder the propagation of the electromagnetic field, thus prolonging the observation of the lower waterlogged goafs and reducing the signal-to-noise ratio. Besides, the burial depths and layer spacings of double-layer waterlogged goafs affect the signal-to-noise ratio and the observation time of transient electromagnetic signals. By building a double-layer waterlogged goaf model based on the Majiayan coal mine in Shanxi, this study analyzed the electromagnetic field propagation under layer spacings of 25 m, 50 m, 75 m, and 100 m,and calculated the observation time of waterlogged goafs with different layer spacings. Furthermore, it quantitatively characterized the differences between induced voltages in the double-layer waterlogged goafs with different layer spacings using root mean square errors. Additionally, this study proposed the identification criteria for explorable lower waterlogged goafs based on the record errors and noise levels during the observation. The results of physical simulation experiments are as follows: The differences between the induced voltages of double-layered waterlogged goafs with different layer spacings occur mainly in the late stage; the differences between induced voltages gradually decrease as the layer spacing and the burial depth of upper waterlogged goafs increases; the difference between induced voltages is close to the noise level when the layer spacing is greater than 75 m. The actual detection of the double layer waterlogged goaf with a spacing of 75 meters was conducted in Majiayan Coal Mine, and the results showed that the lower waterlogged goaf was not effectively identified.Therefore, It is difficult to effectively explore the lower waterlogged goafs when the layer spacing is greater than 75 m.

Airborne geophysical surveys, characteristic of being green, economical, efficient, and subjected to less influence by surface factors, serve as the one of most effective means of basic surveys and scientific research on the Qinghai-Tibet Plateau. This study reviewed the progress in the airborne geophysical surveys in the Qiangtang Basin of the Qinghai-Tibet Plateau in the past thirty years, systematically summarizing the progress and geological interpretation results of comprehensive airborne geophysical surveys in the basin. Furthermore, this study presented research progress and understanding of major basic geological issues of the basin, such as the basin's boundaries, central uplift zone, basement properties, deep structures, and cover characteristics, as well as the identification of favorable structural areas for oil and gas exploration. Finally, based on an analysis of the developmental trends of airborne geophysical surveys in the Qiangtang Basin, this study proposed opinions and suggestions for key research directions in the future.

Huize County of Yunnan Province is situated in the karst area in southwestern China, where karst groundwater is its primary water source. To conquer local difficulties in drinking water, this study constructed a conceptual model of groundwater occurrence by fully investigating the hydrogeological conditions of the Huize area. Moreover, this study evaluated the applicability and optimal combination of geophysical methods based on the measurement results of petrophysical properties. According to the actual local needs, this study deployed a comprehensive profile combining high-density electrical resistivity tomography (HDERT) and audio magnetotellurics (AMT) in Tuogu Village, Huize County. The groundwater enrichment site was delineated relying on resistivity anomalies, effectively guiding the layout of boreholes. The boreholes achieved the maximum single-borehole water yield of 20.76 m³/d, thus effectively alleviating the local drinking water problem. The HDERT-AMT combined exploration method proves to be optimal for prospecting for groundwater in carbonate rock areas. HDERT can accurately characterize weathered layer thicknesses, bedrock boundaries, fissure evolutionary degrees, and water-bearing properties of strata, constraining groundwater recharge channels, thus counteracting AMT's defects for identification of near-surface stratigraphic structures. AMT can accurately reflect the spatial structures of fracture zones and the macrostructures of strata, limiting the boundary conditions (aquicludes) of water-bearing structures, thus making up for the defects of insufficient detection depths of HDERT in high-resistivity stratigraphic regions. HDERT and AMT, which are complementary to each other in terms of accuracy and depth, can be applied to identify and constrain the spatial occurrence conditions of groundwater migration, storage, and enrichment.

The grounded-source transient electromagnetic (TEM) method, which enjoys the advantages of high topographic adaptability and large exploration depths, is suitable for deep resource exploration in mountainous areas. However, the TEM responses can be distorted due to topographic effects, causing great difficulties in data interpretation. This study investigated the influence patterns and correction method of topographic effects based on the three-dimensional unstructured time-domain finite element method. First, this study conducted the fine-scale description of mountains using unstructured tetrahedral grids, calculated the response of various topographic models, and analyzed the influence patterns of topographic effects. Then, it proposed a correction method for topographic effects based on the principle of the linear superposition principle of electromagnetic fields, established a geoelectric model of mountains according to the actual elevation data, and calculated the model responses through three-dimensional forward modeling. Subsequently, this study determined the topographic responses by subtracting the flat Earth model responses from the mountain model responses and then obtained the corrected TEM responses by removing the topographic responses from the total responses. The results are as follows: (1) The influence of mountains on the TEM responses is concentrated in the early stage and weakens gradually with time; (2) The topographic effects are concentrated near mountains, and their intensity depends on the distance of survey points from mountain peaks; (3) The influencing range and response amplitude of mountains are proportional to the mountain scale. In other words, a larger mountain scale corresponds to a larger influencing range and higher response amplitude; (4) Mountains with relatively high resistivity show more intense topographic influence. As shown by multiple models with simple and regular topographic anomalies, the corrected TEM responses, which match well with the responses from direct forward modeling, can effectively eliminate topographic effects to a certain extent. The research on the influence and correction method of topographic effects can be used as a reference for the processing and interpretation of TEM data of areas with complex terrain.

Since individual geophysical exploration methods suffer the multiplicity of solutions, comprehensive geophysical prospecting has been extensively applied in deep ore prospecting presently. This study conducted the geological exploration of the Duhu porphyry copper deposit in Xinxing County using multiple geophysical methods such as high-precision magnetic survey and controlled source audio-frequency magnetotellurics (CSAMT). It was inferred that the CSAMT-derived medium-low resistivity anomalies and the low-gentle anomalies derived from the high-precision magnetic survey serve as significant prospecting indicators. Satisfactory results were achieved in follow-up verification of the anomalies. Specifically, copper, molybdenum, silver, and gold mineralized bodies with a cumulative thickness of 178.2 m were identified in a 1 000 m deep borehole, with the highest copper grade of 1.45%. The application of comprehensive geophysical prospecting holds great significance in guiding the exploration of porphyry copper deposits in western Guangdong.

With the rapid development of cities and the accelerated construction of subway tunnels,there is an urgent demand for the detection of unfavorable geological bodies ahead of tunnel excavation.It is difficult for traditional electromagnetic methods to yield excellent detection results in an urban environment with high electromagnetic interference.Active-source surface wave exploration has gained increasing popularity in shallow superficial exploration and engineering geophysical prospecting in cities due to its strong anti-interference,convenient acquisition devices,and low construction cost.However,the traditional active-source reflection seismic method uses only a heavy hammer with limited excitation energy as a seismic source,and the collected signals are prone to be disturbed by urban activities.Meanwhile,the asphalt or cement pavement in urban areas is unfavorable for the placement of geophones and the excitation of seismic signals from a hammer.Given these,this study improved the geophones and seismic source devices at low costs,obtaining a more efficient and user-friendly surface wave acquisition device.As confirmed by practical engineering exploration,the improved device can collect surface-wave signals with strong energy and high signal-to-noise ratios,resulting in high-quality data,desirable inversion and imaging results,and high consistency between the geological defects and actual geological conditions.The improved acquisition device can be extensively promoted and referenced in active-source surface wave exploration in cities.

Significant aeromagnetic and gravity anomalies were found in the ultra-deep coverage zone of the Pandian area in the northwestern Shandong Province. Through systematic verification of gravity and magnetic anomalies, a breakthrough in prospecting for deep skarn iron deposits has been achieved through several boreholes around the Pandian gravity-magnetic anomaly zone. However, the gravity-magnetic anomaly zone spreads extensively and its characteristics cannot directly indicate the prospecting target, thus some boreholes failed to find ores or revealed poor ore-finding conditions. Hence, to accurately delineate the ore-forming location in the gravity-magnetic anomaly zone and achieve a further breakthrough in ore prospecting, this study conducted the wide-field electromagnetic (WFEM) sounding in the verified Pandian gravity-magnetic anomaly zone. Combining the drilling verification, this study delineated the deep ore-forming interval of skarn iron deposits in the deep coverage zone and the favorable structural plane for ore-forming, suggesting the deep fine-scale prospecting targets.

The performance of ray-based tomography inversion is affected by many factors,such as initial model error and low-velocity interlayer.The conventional tomography method based on first-arrival wave travel time,which constrains or smooths models,destroys the relative relationship between model parameters and rays and affects the inversion stability.By testing the performance of first-arrival wave travel time-based tomography inversion under different initial models,this study proposed a first-arrival wave travel time-based tomography inversion method with surface wave information as constraints.The process of this method is as follows:(1)Given that surface waves feature high energy and frequency dispersion in seismic data,the surface-wave frequency dispersion curves are obtained through the multi-channel analysis of surface waves;(2)Using the damped least squares method,the shallow-surface shear wave (S-wave) velocities are determined through inversion;(3)With the S-wave velocity structure as the constraint,the initial compressional wave (P-wave) model is established,and accordingly,the first-arrival wave travel time-based tomography inversion that considers regularization is achieved.This method improves the accuracy and stability of shallow structure inversion by fully utilizing the surface wave information in seismic data to counteract the inherent defects of tomography inversion.The effectiveness of this method has been verified using actual data.

To explore the critical factors influencing the results of microtremor-based exploration at a depth of thousands of meters,this study conducted experiments using triangular arrays based on spatial autocorrelation(SPAC) and extended SPAC(ESPAC).Focusing on factors such as array size,acquisition unit frequency,and acquisition duration,this study explored the frequency band ranges corresponding to different array sizes,the arrangement of arrays in kilometer-depth exploration for obtaining both deep and shallow data,and the improvement in deep resolution.Based on the analysis and discussion results,this study established a parameter-setting system to improve the accuracy of exploration at a depth of thousands of meters.

This study aims to ascertain the distribution patterns and influencing factors of fluorine in irrigation water and soils in the Gaomi area, Shandong Province, China. Through systematic sampling and testing, this study obtained data including the pH and fluoride concentration of irrigation water and the pH, organic matter, and fluorine concentration of soils. Based on these data, this study plotted the geochemical contour maps for statistical, correlation, and difference analyses. Furthermore, this study explored the influencing factors. The results are as follows: (1) The irrigation water in the study area has a fluoride concentration of 1.89 mg/L on average, which shows strong spatial variability. Zones with high fluoride concentrations in irrigation water are distributed in the northern low-flat alluvial plain, with the number of samples with fluoride concentrations greater than 2 mg/L accounting for 63.16%. There is a significant positive correlation between the fluoride concentration in the irrigation water and the pH (P < 0.01); (2) The soils have a fluoride concentration of 455×10^-6 on average, which shows an inhomogeneous spatial distribution. Zones with high or excess fluorine concentrations are distributed in the northern part of the study area. The fluorine concentrations of soils show significant positive correlations with the pH and organic matter of soils and the fluoride concentration of irrigation water (P < 0.01); (3) The fluoride concentrations in the irrigation water and soils are high in the distribution area of lime concretion black soil. The results of this study reveal the background characteristics and influencing factors of fluoride in the irrigation water and soils of the Gaomi area, providing a geochemical basis for the precise prevention and control of endemic fluorosis.

Magnetotelluric sounding (MT) has been extensively applied in mineral resource exploration. However, strong anthropogenic electromagnetic interference severely constrains the acquisition of high-quality original MT data. This study provided a detailed summary of the common types of electromagnetic noise sources in China and analyzed the characteristics of electromagnetic noise they produced. By comparing the methods for MT electromagnetic noise reduction at home and abroad, this study developed a rapid and effective construction and processing technology for MT data denoising in high-interference ore districts based on actual production demands. The results indicate that Robust processing, remote reference technique, and manual selection are effective and necessary in enhancing MT data quality. Besides, theoretical calculations suggest that the distance between the remote reference stations should be set at 3.56-fold skin depth or above, as verified by the MT experiments in the ore district of the Hongze salt basin, Jiangsu Province.

Xiong’an New Area is one of the areas with the best conditions for the development and utilization of geothermal resources in sedimentary basins of eastern China. Wumishan Formation of Jixian System is the main thermal reservoir, with buried depth of the top boundary varies greatly, which istypical carbonate type thermal reservoir. In order to find out the stratigraphic structure and concealed faults within 6 km of the starting area of Xiong’an New Area, focus on finding out the spatial distribution and structural characteristics of the main deep thermal reservoirs, and predict the favorable geothermal areas, the time-frequency electromagnetic method is applied to the geothermal resources exploration of Xiong’an New Area. Through high-standard data acquisition, refined data processing and resistivity-constrained inversion, the pseudo-seismic imaging technology and borehole data are used to calibrate the resistivity horizon, which effectively improves the reliability of interpretation results. In this work, 8concealed faults were identified, mainly NNE strike normal faults, which controlled the salient-depression pattern and stratigraphic distribution of the study area. The study area is divided into Rongcheng salient, middle sub-depression, Niutuozhen salient and Baxian depression from west to east. The thermal reservoirs of Wumishan Formation is mainly distributed in Niutuozhen salient, Rongcheng salient and middle sub-depression, with buried depth of top interface is about 600~2600m. Vsing the inversion results of the time-frequency electromagnetic method, the three-dimensional geological model of the study area is constructed, and the Niutuozhen salient area is considered to be the optimal geothermal favorable area from the aspects of heat source, channel, reservoir, caprock and fluid, especially near the footwall of F₄.

Audio magnetotellurics (AMT) is widely used for energy and mineral explorations because of its high exploration efficiency and high vertical resolution. Using a three-dimensional (3D) inversion algorithm based on data space, this study performed 3D inversion of the AMT data collected from geothermal exploration in the Santunhe area of Xinjiang. As indicated by the inversion results, the 3D inversion avoids the influence of inhomogeneous geobodies on the survey lines in the study area and yielded very rich and intuitive 3D geoelectric anomalies. In combination with the geological data and the 3D inversion results, this study analyzed the subsurface electrical properties of the study area and the formation water-bearing properties related to geothermal reservoirs, and finally inferred several favorable areas for geothermal reservoirs from the geothermal accumulation patterns of the study area.

Ground-penetrating radar (GPR) data are often contaminated by random noise in the actual engineering inspection.The noise in data will reduce the signal-to-noise ratio and resolution of the data,adversely affecting the subsequent inversion and interpretation.Accordingly,this study proposed neural network-based denoising for GPR data.First,a multi-layer neural network model was constructed to integrate the data corrupted by white Gaussian noise into the noise-free data.Then,the corrupted data and their corresponding noise patches were built as training data.The weights of neurons in every layer of the model e updated using a back-propagation algorithm to minimize the model training loss.Finally,the two synthetic data and the measured radar data were input to the trained model,and the model's output was calculated using the noise characteristic weights acquired from the training.Compared with the curvelet transform,the numerical simulation test results verify the effectiveness and robustness of the method proposed in this study.Moreover,the proposed method can suppress the noise more thoroughly in areas with complex structures and weak amplitudes,and show effective signals more clearly.

Airborne gravity-magnetic data are effective in revealing the deep structures of a basin.Based on the latest airborne gravity-magnetic data,combined with field-measured physical property data,this study expounded the characteristics and geological origin of airborne gravity-magnetic anomalies present in the Baiyunhu sag.Using the airborne gravity-magnetic data,this study identified the distribution of faults and magmatic rocks in the Baiyunhu sag.Furthermore,it calculated the burial depth of the magnetic basement and the structural morphologies of the Mesozoic basement in the sag using the artificial tangent method, power spectrum analysis method,and Parker-Oldenburg iterative inversion algorithm.Additionally,this study verified the structural stratification results through the integrated interpretations of gravity and magnetism in target sections.The findings suggest that the undulations of the Mesozoic and Paleozoic sediments in the Baiyunhu sag are the primary cause of gravity anomalies,while the regional airborne magnetic anomaly primarily reflects the distribution features of the Precambrian basement.The deeply buried basement of the Baiyunhu sag,featuring continuously distributed,thick Mesozoic strata and the lack of regional faulting and magmatic activity,is scarcely affected by tectonic movements and possesses great potential for oil and gas exploration.

Southern China boasts great potential for normal-pressure shale gas resources,with distribution areas primarily including the peripheral complex structural areas and the extrabasinal fold belts of the Sichuan Basin.These areas exhibit intricate surface and subsurface geological conditions,leading to poor seismic acquisition quality,low imaging accuracy,and unclear varying patterns of sweet spot parameters.This study systematically summarized the research achievements and technical advances in the seismic acquisition,image processing,and reservoir prediction for normal-pressure shale gas in southeastern Chongqing,including:①The development of variable-density 3D observation system design technique and the seismic excitation and reception technique for complex mountains with limestone surfaces,ensuring sufficient sampling of the reflected wave field in complex subsurface structures and improving data quality and construction efficiency;②The optimization of prestack seismic preprocessing technique for complex mountains,imaging techniques for complex structures in basin-margin transition zones, and imaging techniques for synclinal structures in extrabasinal fold belts,achieving resulting profiles with high signal-to-noise ratios,wide effective frequency bands,and high structural imaging accuracy;③The quantitative prediction of the thickness,formation pressure coefficient,and brittleness of high-quality shales based on research on petrophysical characteristics;the quantitative prediction of the organic carbon content,gas content,and porosity of shales based on statistical petrophysics;the quantitative prediction of fractures formed due to the superimposed effect of multi-stage structural modifications based on the paleo-stress field evolution revealed using the finite element simulation technique;and the ascertainment of the distribution patterns of the current in-situ stress field using the current stress field prediction technique developed using the combined spring model.The above breakthroughs have effectively guided the sweet spot prediction,exploration,and production of normal-pressure shale gas,providing a basis for the discovery of the Nanchuan normal-pressure shale gas field.Subsequent research should focus on more scientific and reasonable seismic acquisition techniques based on seismic reception using 5G wireless nodes,high-precision automatic image processing technologies for high-steep structures in complex mountains,and integrated geology-engineering-economy seismic evaluation methods for sweet spots.

In geoscientific field, the essential object of all the research problems is the physical world which is derived from the crust-mantle interaction and has deeply influenced globally the environment and resources. The metallogenic geochemical theory believes that the metallogenic materials are the internal factors for the metallogenic system to influence the metallogenic process, and taking metallogenic materials as the main body to study the problems of metallogenic materials and metallogenic processes is the basic meaning of the metallogenic geochemical theory, and the core subject of the studies of metallogenic rules and theories. During the mineralization process of metallogenic system, metallogenic materials formed into metallogenic series of corresponding scale. This paper outlines several scientific topics of the metallogenic geochemical studies, among which, the topic of global metallogenic system mainly studies the metallogenic processes and relations of the series of metallogenic regions, provinces and belts formed by metallogenic materials in the context of global metallogenic process; the topic of regional metallogenic system mainly studies the metallogenic processes and relations of ore field series in the context of regional metallogenic process; the topic of ore field metallogenic system mainly studies the metallogenic processes and relations of mineral deposit series in the context of ore field metallogenic process; the topic of mineral deposit metallogenic system mainly studies the metallogenic processes and relations of ore-body series in the context of mineral deposit metallogenic process. The basic research ideas concerning above mentioned studies are discussed in this paper, including the metallogenic materials' geneses and sources, migration and evolution, differentiation and concentration, as well as the zoning relations of each level's metallogenic system and series of the world during the metallogenic processes. The purpose is to summary the metallogenic rules, explore the metallogenic mechanism and guide the mineral resources exploration. Supported by modern technologies and methods of IT(information technology), modeling and AI(artificial intelligence), the metallogenic geochemical theory uses the earth system scientific ideas to study the problems of metallogenic system and metallogenic series, construct the theoretical framework for metallogenic geochemical research, and provide a theoretical basis for the mineral resources exploration, evaluation and development technics and methods.

Given large data volumes and low post-processing efficiency of full matrix capture-total focusing imaging,this study proposed a planar array-total focusing method(PATFM) for the imaging of planar array data.First,the wave front time of the downgoing planar array was calculated using the eikonal equation based on the characteristics of both the total focusing imaging algorithm and the planar array wave field.Then,the total focusing imaging formula was improved using the upgoing and downgoing ultrasonic propagation time based on the delay superposition principle.Finally,focusing imaging was performed on a wide range of imaging points below the planar array aiming at the derived directivity and diffusion correction coefficient of the planar array.Through Field II simulation,the PATFM was compared with three imaging methods,including phase-controlled scanning imaging,full matrix capture-based total focusing imaging,and plane wave capture-based total focusing imaging.The results show that the PATFM can be used for large-range focusing imaging of single planar array data,greatly improving the computational efficiency while obtaining corresponding accuracy.Therefore,this study provides a feasible technical means for 3D imaging of array acoustic waves.

The transient electromagnetic method (TEM) commonly uses the all-time apparent resistivity parameter for interpretation, which involves complex formulas and time-consuming iterative processes. Based on the characteristics of TEM data, this study employed the artificial neural network (ANN) for TEM pseudo-resistivity imaging. First, this study designed a multi-hidden-layer BP neural network and calculated a response amplitude through TEM analysis. The response amplitude, as the mapping parameter of pseudo resistivity, was used for network training. Then new data outside the training set were used to test the trained network. A homogeneous half-space and one-dimensional layered model was built to verify the correctness and adaptability of the neural network. The imaging of the three-dimensional geoelectric model was performed. As revealed by the results, the pseudo resistivity calculated based on the neural network can reflect the target anomalies of the geoelectric model, with highly accurate network imaging results. Finally, the measured data were processed using the neural network algorithm, further indicating that the neural network-based imaging can serve as a basis for data interpretation. This study verified the feasibility of the ANN in TEM imaging, thus providing a new approach for TEM imaging.

This study aims to ascertain the heavy metal pollution of groundwater in a typical chemical industry park in northwestern Shandong. According to the investigation and evaluation requirements for groundwater environments in chemical industry parks, this study collected 10 groundwater samples to analyze the concentrations and spatial distributions of eight heavy metals, namely Fe, Cu, Zn, Al, Cd and Pb. Furthermore, it conducted the health risk assessment of groundwater for different populations. The results indicate that: (1) except Mn and Al, all heavy metals in the groundwater of the chemical industry park showed concentrations lower than the class III water quality standard stated in the Standard for Groundwater Quality (GB/T 14848—2017), with a comprehensive pollution index ranging from 0.37 to 0.78. The monitoring points for heavy metal elements are all pollution-free; (2) the overall spatial distributions of heavy metals are roughly consistent with the distribution areas of key enterprises in the chemical industry park. This consistency indicates that external factors such as the production activities of enterprises affect the spatial distributions of heavy metals in groundwater; (3) the health risks are lower for children than for adults and lower via skin contact than via drinking. The non-carcinogenic risks under different exposure routes are acceptable for different populations. Carcinogens As and Cd have slight carcinogenic risks for adults. Local authorities should strengthen the supervision of the production activities of enterprises and thoroughly inspect enterprises with suspected pollution. Only in this way can we effectively control and then gradually reduce the risks to human health caused by groundwater pollution.

This study aims to systematically investigate the distribution and over-limit elements of areas with high geological background values of heavy metals in soils in Yunnan Province. GIS spatial analysis was conducted based on the heavy metal content data from a province-wide 1∶200,000 stream sediment survey and the regional geological map. The analysis results were validated using the data of heavy metals in soils in Kunming, Yuxi, Zhaotong, and other regions. A total of 61 geological units were identified, with heavy metal content in soils exceeding the screening values of agricultural land, accounting for 21.09% of the total land area of Yunnan. The cultivated land in high geological background areas covers an area of approximately 2.844 1 million hectares, accounting for 7.22% of the total land area of Yunnan. The lithologies that cause over-limit heavy metals in soils primarily comprise carbonate rocks, mafic-ultramafic volcanic rocks, intermediate mafic intrusive rocks, coal-bearing clastic rocks, and clastic rocks with mafic components. The over-limit heavy metal elements in high geological background areas are dominated by Cu, Cr, Ni, and Cd. In contrast, As manifests an over-limit risk mainly in carbonate rock formations, Pb and Zn only exhibit an over-limit risk in individual strata, and Hg almost shows no over-limit risk.

Cumbersome acquisition tools and laborious indoor data processing are bound to impair the quality and accuracy of conventional field geochemical surveys, especially in study areas with many samples and a harsh natural environment. The informatization and intelligence of field geochemical surveys are the requirements of the times and an inevitable trend for the advancement of methods and technologies. Based on the ArcGIS and Android platforms, this study developed a geochemical field sampling system, which comprises task planning, field data collecting, quality control, and other functions, to match the field geochemical survey process using mobile GIS and database technologies. This system enables the informatization and intelligence of the entire field geochemical survey process, simplifying the data collection procedure, reducing the time needed for fieldwork, and enhancing the data collection efficiency. Therefore, this system improves the quality and accuracy of field survey information, advancing the digitization of field geochemical surveys.

The Dongfang 1-1 structure is situated in the northern part of the central mud diapir tectonic belt of the Yinggehai Basin on the northern continental shelf of the South China Sea.The Dongfang 1-1 gas field is the first uncompartmentalized shallow gas field discovered in the Yinggehai Basin.Despite abundant oil and gas reserves in this region, the imaging of the diapir fuzzy zone has been a critical factor restricting oil and gas exploration in this region.The original streamer-based seismic data,through multiple rounds of multi-company reprocessing,still failed to effectively image the diapir fuzzy zone.Therefore,the second acquisition of three-dimensional ocean bottom node(OBN) seismic data was conducted in this region.According to the geological conditions and the characteristics of OBN data in this region,this study proposed several critical processing techniques,including OBN preprocessing,multi-component joint shear-wave noise suppression,wavelet-domain dual-sensor summation,and full-waveform-inversion(FWI) high-precision velocity modeling.These techniques effectively improved the imaging of shallow fault structures and middle and deep diapir fuzzy zones,thus providing reliable fundamental data for the subsequent target evaluation.

Due to various strong electromagnetic mechanical interference and traffic barriers, many geophysical exploration techniques are ineffective in urban geophysical exploration.Based on transient surface waves,microtremor arrays,and microtremor spectral ratios,this study synthetically extracted two kinds of characteristic curves for joint inversion from the multi-source frequency-domain seismic data obtained by multi-point three-component low-frequency sensors.Consequently,this study achieved multi-source frequency-domain seismic exploration that integrated three techniques and developed the two-source synthetic dispersive spectrum extraction technique,the two-source characteristic curve joint inversion technique,and the equivalent homogeneous medium forward modeling technique based on inhomogeneous media.Engineering practice results demonstrate the improvements in the exploration accuracy and efficiency.

The joint processing and integrated interpretation of multi-source geophysical exploration data are indispensable to the exploration evaluation of deep geothermal resources. Joint inversion and post-inversion geological differentiation are two major hot research topics in deep resource exploration. To integrate the multi-source geophysical field information and reduce the inversion multiplicity of single geophysical fields, this study built a structural model using the stratigraphic structure information from seismic interpretation, with the prior information of petrophysical properties as a guide. This study constrained the stratigraphic geophysical parameters using the Gaussian mixture model and conducted regularized joint inversion of gravity, magnetic, and magnetotelluric data, thus achieving the coupling of multiple physical structures. Finally, this study developed the software for the joint inversion of gravity, magnetic, magnetotelluric, and seismic data. Based on the joint inversion results and electrical resistivity, this study predicted the temperature field at typical hot dry rock sites using the Arrhenius law. The forward modeling results of the theoretical model for cubic anomalies were used for the joint inversion. Compared with individual inversion, the joint inversion performs well in the spatial characterization of anomalies and the recovery of physical property values. Furthermore, the joint inversion can fully integrate multiple data on geology, petrophysical properties, and geophysics, thus well conforming to the actual conditions.

The Tiaojishan Formation in northwestern Hebei Province is home to volcanic-sedimentary strata. Due to the lack of fossil organisms, insufficient isotopic dating data, and outdated dating methods, the formation epochs of these strata have been controversial. To accurately determine their formation epochs and examine their regional geotectonic setting, this study conducted a detailed field investigation of the lithologic assemblage of the Tiaojishan Formation in the Xuanhua Basin. Petrological, petrogeochemical, and high-precision isotopic dating studies were conducted on the trachytic volcanic rocks in the upper segment of the formation, obtaining the LA-ICP-MS-based zircon U-Pb isotopic ages, which were 161.1±1.2 Ma and 162.5±1.3Ma. As indicated by the petrological and petrogeochemical characteristics, these trachytic volcanic rocks belong to the shoshonite series, exhibiting enriched light rare earth elements, relatively enriched elements including Rb, K, Th, Ce, Zr, and Hf, and relatively depleted Ba, Nb, Sr, P, and Ti. According to the comparison of principal parameters and graphical discrimination, the magma originated primarily from the melting of continental crustal materials and formed in the tectonic setting of compressional continental margin volcanic arcs. The comprehensive research reveals that the Tiaojishan Formation formed primarily during the Middle Jurassic and continued to the Late Jurassic, and the trachytic volcanic rocks in its upper segment formed in the intraplate compressional tectonic setting. The results of this study provide new data for the division and correlation of Mesozoic volcanic-sedimentary strata and the analysis of their formation environment.

Investigating the spatial distribution of permafrost is critical for cryosphere research. At present, China's investigation concerning the spatial distribution of permafrost generally employs the detection method of ground geophysical exploration combined with logs to obtain local point or line data. Alternatively, different remote sensing models can be used to simulate and estimate the thickness of regional permafrost. This study inferred the spatial distribution of permafrost based on airborne time-domain electromagnetic (TDAEM) data and resistivity calculation results. The comparative analysis of the inference results and the known drilling data reveals an average error of 18.5% between the permafrost thickness inferred from the inversion results of TDAEM data and the result determined by borehole temperature measurements. This suggests that the TDAEM method exhibits high effectiveness and accuracy in permafrost thickness investigation. With technical advantages like high efficiency and minor topographic influence, the TDAEM method can be applied to the large-scale, rapid, and quantitative permafrost investigation in the Qinghai-Tibet Plateau and the Greater Khingan Range in northeast China. Therefore, this study provides a new and effective technical solution for a comprehensive investigation of the spatial distribution of permafrost and its influence on ecological environment changes.