The northeastern margin of the Linyi uplift is located at the eastern end of the Luxi Block and immediately adjacent to the Yishu fault in the east. The main structural framework of the study area is controlled by the NE-trending Tangwu-Gegou fault and the NW-trending Mengshan fault. Covered by the Cenozoic sediments, the boundaries of main tectonic units in the study area are almost all concealed, and it is necessary to further investigate the change in the strike of the eastern end of the Mengshan fault as well as the distribution of the angular unconformity along the northern boundary of the Linyi uplift. Using the latest 1:50,000 high-precision gravity data, this study mainly investigated the positions and intersection relationships of the boundaries of tectonic units based on the qualitative analysis of gravity field, the interpretation of multiple gravity potential field conversion, and the division scheme of geotectonic units in Shandong Province. The analysis results are as follows. The Mengshan fault at the junction of the Mengshan uplift and the Pingyi sag transitions from the NW trending to nearly-EW trending in the east of Bancheng Town, significantly cuts the NE-trending Tangwu-Gegou fault, and shows a NW-trending turn to the east again. The angular unconformity at the junction of the Linyi uplift and the Pingyi sag neither ends in the Mengshan fault in the north nor turns southward but extends to the Tangwu-Gegou fault in the east. This unconformity also controls the southern boundary of the Pingyi sag, making the NW-trending banded gravity anomalies of the sag turn eastward. Consequently, the boot-shaped low-value gravity anomalies were formed in the study area. Based on the high-precision gravity boundary identification, this study determined the fault system and tectonic division of the northeastern margin of the Linyi uplift, providing high-precision gravity data for the basic geological study in the study area and laying a good foundation for further mineral geological survey.

Based on the data on the geology, minerals, exploration, and geochemistry of more than 30 fluorite deposits in the Heyu-Checun area, western Henan Province, this study summarized the types, spatial distribution, and geochemical characteristics of fluorite deposits in the area and explored the genesis and material sources of the deposits. The fluorite deposits in this area have simple types and are distributed in Yanshanian granites and along the fault zone of the external contact zone of the granites. The formation ages of the Heyu and Taishanmiao plutons are 124.7~148.2 Ma and 115~123.1 Ma, respectively. The mineralized age of fluorites is 120~126.8 Ma, indicating that the mineralization occurred in the late stage of the intrusion of the Heyu pluton and the early stage of the intrusion of the Taishanmiao pluton. The ore-forming fluids belong to the NaCl-H₂O system with a medium-low temperature, a low salinity, and a low density, indicating that the deposits in the area are medium-low-temperature supergene hydrothermal fluorite deposits. The chondrite-normalized REE patterns of fluorites in the area can be divided into slightly leftward, flat, and rightward types dominated by the rightward type. Moreover, the rightward chondrite-normalized REE patterns of fluorites are similar to those of the Yanshanian granites, both showing strongly negative Eu anomalies and weakly negative Ce anomalies. This finding indicates that the Yanshanian granites provide materials for the formation of fluorites. The metallogenic element F may mainly originate from the Heyu and Taishanmiao plutons, while the metallogenic element Ca partly comes from granites as surrounding rocks.

This study developed a workflow of Rayleigh-wave dispersion inversion using the Python programming language, and the detail is as follows.First,carry out the forward modeling of the dispersion curves on a horizontal layered model using the pysurf96 software package.Second,create an objective function used to describe the fitting degree of the dispersion curves.Third,complete the dispersion curve inversion using the heuristic algorithm in the scikit-opt software package.The problems encountered in the function call in the workflow were proposed and solved.The results show that the Python-based dispersion curve inversion of Rayleigh wave in multilayered media is reliable and offers a certain computational efficiency.In this way,this study built a Python-based inversion platform of underground layered structures using the wave dispersion,thus providing a method for other researchers to do inversion using open-source software.Finally,this study carried out the inversion of the crust and upper mantle structures using the dispersion curves extracted from the study of Yi-bo Peng on the noise in the Hailar Basin,achieving ideal results.

Due to the strong attenuation effect of loess cover on seismic and electromagnetic waves, the successful application of seismic reflection wave method and electromagnetic wave method in loess covered area is limited.In view of the characteristics of large thickness and fine stratification of loess cover, the active source and passive source surface wave methods are combined in this paper, so that the advantages of the two surface wave methods are complementary and the geological stratification of loess covered area can be accurately detected.The study area is located in the suburb of Fengxiang County,Weihe Basin.It is a typical loess covered area, and the thickness of loess cover is 80~120 m.By processing the measured data of active and passive surface waves in the study area, the positions of the main strata on the 2D shear wave velocity profile are basically consistent with the actual borehole test results, and the 3D stratum structure in the study area is also obtained.The results of joint imaging show that it is feasible and effective to use passive and active surface wave joint exploration for stratification of loess covered area, which provides technical support and beneficial idea for geological mapping of loess covered area.

This study summarized the progress and major application performance of gravity and magnetic techniques for onshore hydrocarbon exploration in China in recent years.By combining the research results of the authors,this study elucidated the new progress made in the gravity and magnetic techniques for hydrocarbon exploration from the prospect of acquisition,processing,interpretation,and application and sorted the application performance of these techniques in key fields including deep targets,complex areas,and volcanic rocks.Moreover,this study future analyzed the demand for the gravity and magnetic techniques for hydrocarbon exploration.By combining the new trends of gravity and magnetic exploration techniques at home and abroad,this study proposed the development direction and application prospect of gravity and magnetic techniques for oil and gas in deep strata and igneous rocks in complex areas.The results of this study show that significant progress has been made in gravity and magnetic exploration techniques,which play an important role in supporting the current hydrocarbon exploration.It is expected to develop high-precision and high-density gravity and magnetic exploration techniques and gravity-gravity-electricity-seismic collaborative innovation techniques.

As resource exploration deepens and becomes increasingly difficult,improving the imaging precision and the reservoir prediction accuracy under a complex tectonic setting has become a top priority of research.The full waveform inversion (FWI) method developed in recent years can be applied to complex geological structures.This method can reveal structural details in a complex geological setting using the dynamic and kinematic information in the pre-stack seismic wave field.However,this method involves many research elements such as model parameterization,building of inverse error function,data preprocessing,numerical simulation of wavelengths,and wavelet estimation.Thus,its development is bound to be a long-term gradual improvement process.The FWI method has been applied to actual observation data with the development of theory and computer technology.This study introduced the principle and processing flow of the FWI method and summarized its development history and its application status in marine and onshore seismic data,and deep seismic reflection data.Accordingly, this study presented the current application bottlenecks,data processing difficulties, and challenges of deep-crustal inversion imaging for subsequent research and application of the FWI method.

Many karst fracture-vug reservoirs have been found in the Ordovician carbonate paleo-buried hills in the Lungu area,Tarim Basin.Hydrocarbons are mainly enriched in these fracture-vug reservoirs,which are mainly related to the paleo-underground river system in carbonate paleo-buried hills.The paleo-underground river system is well developed,especially in the western Lungu area.The fracture-vug reservoirs related to the paleo-underground river system have strong longitudinal and lateral heterogeneity,and ascertaining the seismic and geological characteristics of the paleo-underground river system in this area is the key to the efficient development of fracture-vug reservoirs in this area.Based on the characteristics of modern karst underground rivers and the log and drilling data of this area,this study established a geological model of underground rivers for forward modeling.The study results are as follows.The underground river system developing under the tight limestone setting showed continuously linear strong reflections on the seismic profile.The seismic amplitude decreased as the height and width of underground rivers decreased,and higher seismic amplitude corresponded to larger underground river caves and lower filling velocity.The amplitude can accurately characterize the horizontal range of the underground river on the seismic profile.Meanwhile,the frequency and phase can describe the outline of the underground river on the seismic profile,but the outline described was larger than that of the real underground river.The main channels of the underground river system were prone to be filled with mud.By contrast,the branch channels had a low filling probability and thus serve as the main areas for both the occurrence of underground river reservoirs and the hydrocarbon accumulation.

The Xiong'an New Area is located in the middle part of the Jizhong Plain.The Cenozoic strata in the underground structure of the area have a large thickness,good stratification,and relatively stable tectonic activities.To finely determine the shallow geological structures,ascertain the fault structure characteristics,and improve the shallow exploration accuracy,this study combined two-dimensional seismic surveys and high-density resistivity sounding and made the following important progress.①This study finely determined the geological structure and the spatial distribution characteristics of fault structures at a depth of less than 200 m in the Xiong'an New Area;②This study constructed a three-dimensional visualized geological structure model,which intuitively displays the stratigraphic fluctuation pattern of Cenozoic strata and the spatial distribution of main fault structures;③This study analyzed and summarized the application of geophysical methods under the background of urbanization-induced high disturbance,including their exploration depths,horizontal and vertical resolution,response characteristics of geological bodies,and applicability.This study effectively supports and serves the planning,construction,and underground-space development and utilization in the Xiong'an New Area and serves as a reference for the geophysical exploration of urban underground space in hugely thick sedimentary basins.

The heavy metal element contents in soil affect the quality of soil environment. Their prediction using different models based on survey data is an important means to study the changing trends of soil element contents and soil environmental quality. Based on the data from 1∶250 000 multi-purpose regional geochemical surveys and 1∶50 000 land quality geochemical assessments, this study predicted the contents of five heavy metal elements in the soil of the study area in 2027 using the single-period incremental model and the input-output flux model individually. The results are as follows. The two models yielded different prediction results but consistent trends that the contents of five heavy metal elements increased to different degrees. Moreover, the single-period incremental model yielded larger increments than the input-output flux model. Among the various input channels of the flux model, Cd and Pb entered the soil mainly through dry and wet atmospheric subsidence, As and Cr entered the soil mainly through fertilization, and Hg entered the soil mainly through irrigation water. Based on the survey and prediction data of soil monitoring sites, the soil environmental quality grade was classified for these sites. The proportion of the sites for priority protection showed a downward trend, indicating that the soil environmental quality decreased year by year.

To quickly and effectively detect the hidden hazards of dams,this study proposed the microtremor B-mode ultrasound technology based on linear arrays.Most of the (earth) dams also act as highways,and the vibration signals generated from running vehicles propagate along dams.Therefore,this study proposed deploying linear arrays along the dams,with the vibration propagation direction consistent with the signal receiving direction.In this way,abundant vibration sources can be provided for detecting hidden hazards of the dams.The results of this study show that the data on multiple exploration points can be simultaneously acquired using the multi-channel acquisition technique based on linear arrays,thus improving the efficiency of field data acquisition.Moreover,the influence of source differences can be avoided,and the lateral resolution and the accuracy of exploration results can be improved.The technology proposed in this study was applied to the pre-flood safety inspection of a dam in Jiujiang,Jiangxi Province.Three low-velocity hidden hazards were identified in this dam and were presumed to be the weak layers of the dam foundation and the loose media of the dam body.Practices have proved that this technology effectively counteracts the deficiencies (i.e.,low efficiency and lateral resolution) of the previous microtremor exploration.Moreover,this technology allows scanning at a spacing of 1 m or 0.5 m,thus improving the lateral resolution.This study will provide efficient and accurate guidance for dam safety management.

Ocean bottom electromagnetic receivers (OBEMs) are mainly used for high-precision observation and measurement of magnetotelluric signals and controlled-source electromagnetic signals at the sea bottom. To overcome the shortcomings of large volume, high power consumption, and high cost of the existing OBEMs (OBEM-Ⅲ type), this study conducted technical research regarding miniaturization, low power consumption, and low cost. As a result, the overall power consumption of the existing OBEMs (OBEM-Ⅲ type) has been reduced from 1 600 mW to 500 mW or less (by equipment of inductive magnetic sensors) due to the development of a low-power control unit and preamplifier, the installation of low-power fluxgate sensors, and adoption of advanced power management technology. Traditional acoustic releasers are expensive and bulky and require more suitable buoyant materials. By integrating the underwater acoustic communication module and being equipped with the external erosion wearing release device, the MicrOBEMs make release and recovery possible using only a 17-inch glass sphere, thus greatly reducing the volume and hardware cost of the instrument and improving the integration and operation efficiency of devices. Compared to the OBEM-Ⅲ type, the volume, power consumption, and cost of the newly developed MicrOBEMs are reduced by 3/4, 2/3, and 1/2, respectively. A deep-water geomagnetic test was conducted in March 2021 in the southern South China Sea, preliminarily verifying the geomagnetic measurement function of the MicrOBEMs and reflecting that the MicrOBEMs have the advantages of small size, low power consumption, and low cost.

An ocean bottom electromagnetic receiver (OBEM) is primarily designed to measure the submarine electromagnetic signal. In order to verify the function of the instrument and improve the accuracy of result, the instrument is self-checked by a built-in channel calibration before OBEM enters the water. OBME-Ⅲ needs to export the calibration file generated by channel calibration from the instrument, and then use the Matlab program on the PC side to perform calibration calculation, which has shortcomings such as complex offshore operations and low calculation efficiency. In order to solve these problems, the author developed a calibration calculation program based on the ARM-Linux platform. By entering the relevant commands, the channel calibration calculation can be realized locally in OBEM-Ⅲ, reducing the trouble of exporting data for calculation on multiple platforms. The mixed-base fast Fourier transform calculation method adopted reduces the calculation time from 90 s to 11 s while ensuring the calculation accuracy, which greatly improves the calculation speed and improves the efficiency of the instrument's offshore operations. In the magnetotelluric scientific research mission carried out in the southwest of the South China Sea from July to August 2020, the program performed well and successfully obtained high-quality submarine magnetotelluric sounding data.

To overcome the shortcomings of traditional nonpolarizing electrodes, such as the poor stability of potential difference, high low-frequency noise, short life, and requiring regular maintenance, the authors researched and developed maintenance-free ultra-low noise Pb-PbCl₂ nonpolarizing electrodes after over a decade of development and constant tests. Lab test results show that the new nonpolarizing electrodes have a potential difference drift within one month of less than ±0.06 mV and a temperature coefficient of less than 20 μV/℃, which are 5% and less than one-fifth of those of the PMS9000 electrodes exported from France, respectively; under the ideal condition of the distance between two adjacent electrodes of 100 m, the signal-to-noise ratios relative to the natural induced electric field are 40dB@10³s, 20dB@10⁴s, and 10dB@10⁵s. The field comparative tests show that the newly developed solid nonpolarizing electrodes can significantly improve the acquisition accuracy of geoelectric field signals and the data quality of dead and low magnetotelluric frequency bands.

This study explored the geothermal resources in Yueliangwan, Binhai County, Jiangsu Province using the controlled source audio-frequency magnetotellurics (CSAMT) method and the wide-field electromagnetic method. Through the auxiliary correction of near-field and transition-field curves, as well as the inversion based on the CSAMT data, this study obtained the electrical structure information of underground geothermal resources in the Binhai port. Meanwhile, this study acquired the information on the underground geometric structure using the microtremor exploration method. By comprehensively analyzing the interpretation results of three kinds of geophysical data, this study obtained the geothermal model of the study area and determined the locations of the anomalies. A geothermal well with a depth of 2 919 m was drilled in the study area, obtaining water yield of 2 171 m³/d with a water temperature of 51 ℃. The high consistency between the results from the comprehensive geophysical exploration and the geological and geothermal well data indicates that the comprehensive geophysical exploration method can improve the reliability of geothermal exploration results.

Geothermal measurement is the most direct method to study the distribution of geothermal field. The intensity and distribution of geothermal heat sources directly affect the distribution of the soil temperature field in the surface layer of the earth's crust, especially the existence of thermal reservoirs and thermal transport channels can cause anomalies in the distribution of the geothermal field. Geothermal measurements were carried out in 16 civil wells and 32 boreholes in the study area to analyze the distribution of geothermal field and the pattern of underground hot water activity, and the results were obvious.The results show that the geothermal field at shallow depths is laterally consistent with that at deep depths, with the temperature tending to increase toward the northeastern corner of the study area, and that the anomalous geothermal areas are distributed as a NNE-oriented strip, with a width of about 700 m, which is consistent with the NNE-oriented faults. The highest geothermal point is located at the intersection of the NW and NNE-trending faults.. The vertical geothermal distributions in the study area are distinct. The geothermal water is limited to a narrow area. The low-temperature groundwater inflows into the tectonic faults and karsts, with volumes controlled with the development degrees of them, leading to an abnormal geothermal gradient. This anomaly also indicated that the geothermal water in the Lasozi Mountain area is mainly stored in fissures and karst caves of limy dolomite or breccia rocks, with fissures and caves providing good pathways for the geothermal water to flow. The geothermal measurement method has traced the range of geothermal anomalies in the study area, which provides an important basis for further geothermal investigation.

A geothermal field has been discovered in the Tianshan Sea World on the eastern margin of the Yinchuan Basin, revealing that the region has high-quality geothermal resources. The geological conditions for the formation of the geothermal field are significantly different from those of the conduction-type geothermal resources within basins, providing a new direction for the study of clean energy in the Yellow River Basin in Ningxia. This study processes and analyzes the data of 1∶50,000-scaled gravity surveys, controlled source audio-frequency magnetotellurics (CSAMT), and microtremor survey based on regional geological and geophysical characteristics. The results of the study are as follows. The uplifting zone of the Ordovician basement lies on the east side of the Lingwu Sag and spreads in an "S" shape along the Yellow River Fault. This zone reaches its highest part in the Tianshan Sea World, where it merges with the NW-trending local uplift. The Ordovician of the deep reservoirs in the geothermal field is characterized by medium-high resistance. The Carboniferous-Permian of the first cap rock at a moderate depth shows medium-low resistance and low seismic velocity. The Paleogene-Neogene of the second shallow cap rock corresponds to the formation with low resistance and low seismic velocity. Using these results, three prospective areas for developing and utilization of geothermal resources have been predicted.

The marine controlled source electromagnetic (MCSEM) method is widely used in the exploration of natural gas hydrate, seabed oil and gas resources, and seabed geological structures. In the process of marine operation, the shipborne power supply unit transmits high-voltage and high-power electric power to a marine controlled source electromagnetic transmitter on the seabed through deep towing cables, during which it is necessary to carry out the automatic and real-time measurement and monitoring of the insulation resistance in the high-voltage power supply circuit to ensure the safe transmission of electric energy and timely deal with the abnormal power supply. This study collected the leakage current between the high-pressure end and the ground using high-voltage broadband couplers, insulation detection modules, remote data transmission units, and PC monitoring software. Meanwhile, this study amplified the leakage current using an analog amplifier and then calculated the insulation resistance by measuring voltage, thus achieving the automatic measurement and monitoring of the insulation resistance between the high voltage circuit and the ground. As verified by offshore tests, the automatic online insulation monitoring technology can meet the requirements of the MCSEM system and achieve the ideal online evaluation of the insulation performance of the system, thus providing a useful reference for the research and development of similar functions of marine instruments.

Deep metal deposits tend to be associated with heterogeneous geological bodies on different scales.Moreover,their orefields mostly lie in areas with complex geological structures,developed faults,and intense lithological changes and have complex surface conditions and structures.As a result,the seismic data of metal deposits frequently originate from complex and variable seismic wave fields suffering the mutual inference of multiple types of waves.Therefore,the seismic data have extremely low signal-to-noise ratios,which severely restricts the seismic interpretation of metal deposits and the prediction of concealed orebodies. With the 2D seismic data of the Chaganhua molybdenum orefield in Inner Mongolia as a case study,this study explored the key techniques for the seismic data processing of deep metal deposits.Specifically,this study analyzed the characteristic of seismic data of the Chaganhua molybdenum deposit and summarized the difficulties with seismic data processing of the metal deposit.Based on these,this study developed a set of processes for the data processing of the Chaganhua molybdenum orefield.The actual processing results agree well with the known orebody distribution in the geological borehole section.To be specific,zones with thick ore bodies generated strong reflected energy,while thinner ore bodies exhibited low-amplitude reflected waves.The results of this study can provide strong support for inferring geological structures and delineating concealed orebodies in the study area.

In recent years, prospecting in coverage areas has become an important topic in China due to the strong demand for energy and mineral resources, and there is an urgent need for new targeted methods and technologies of prospecting. This study put forward a technology system for the collaborative and rapid prospecting of copper-nickel deposits in coverage areas that combines airborne-ground-borehole prospecting methods and technologies. Meanwhile, this study established the framework and description of the collaborative, rapid, and effective exploration technology system. Taking the terrain and geology of coverage areas, as well as the distribution characteristics of deep mineral resources in the area as preconditions, this technology system mainly uses the methods of aero geophysics combined with ground and borehole geophysical exploration and focuses on big data fusion, weak information extraction, and geophysical-geological modeling methods. Meanwhile, it takes geological structure and metallogenic theory as guidance. This technical system has been verified in the exploration of the concealed magmatic copper-nickel deposit in the Qixin area, Ruoqiang County, Xinjiang, achieving positive results.

Karst is widely distributed in China. However, geological disasters frequently occur in karst zones due to the fragile geological environment, which seriously threatens the safety of people’s life and property and cause huge economic losses. In this study, the controlled source audio-frequency magnetotelluric (CSAMT) method and microgravity were used to extract residual gravity anomalies through the two-dimensional inversion of pseudosections and multi-scale wavelet analysis. As a result, rock-soil interfaces of karst zones and the development zones of strong karst were well divided; the locations, burial depths, scales, and spatial distribution of karst caves were delineated. As verified by drilling, the rock-soil interfaces and strong-karst development zones determined by CSAMT interpretation were roughly consistent with those revealed by boreholes, and the sizes and burial depths of collapsed karst caves that were delineated by microgravity roughly correspond to those revealed by boreholes of engineering exploration. These results show that the CSAMT combined with the microgravity method can achieve significant effects in the detection of concealed karst collapses and serves as a scientific detection method for the early warning of the prevention and treatment of potential karst collapses and similar geological disasters.

Based on the landscape characteristics of the arid Gobi desert in the Beishan area, Gansu Province, this study carried out a 1:50,000 stream sediment survey in the Sanbaidun area and delineated 10 integrated anomalies. Then, the As-3 anomaly was preferentially selected for detail inspection by taking lithic fragments with grain sizes of 2~20 mm at multiple locations within 1/3 line spacing using a grid density of 100 m × 20 m. As a result, three integrated anomalies of lithic fragments were delineated and their characteristics were investigated. The dominant ore-forming elements were identified as As and Au, and two integrated anomalies were preferentially selected for detailed inspection using methods such as geochemical profile and trenching. Consequently, four Au orebodies, two As orebodies, one Au mineralized body, and one As mineralized body were found. The prospecting results indicate that the geochemical survey of lithic fragments can achieve ideal prospecting effects in the arid Gobi desert landscape area of Beishan and that 1:10,000 surveys of lithic fragments can be used to verify the anomalies of 1:50,000 stream sediment surveys.

Full waveform inversion (FWI) is one of the most accurate velocity inversion tools.It can be used to obtain high-precision subsurface structures through iterative inversion and provide a more accurate velocity field for prestack imaging technology,thus satisfying the increasingly complex demand for petroleum exploration and development.However,FWI requires accurately estimated source wavelets,which are very difficult to extract from the seismic data collected in the field.Furthermore,in the inversion process,there is a strong nonlinear relationship between model parameters and observed data,which is liable to induce cycle skipping.To overcome the cycle skipping and the difficulty in extracting seismic wavelets in the inversion process of medium-low wavenumber,this paper developed a multi-scale waveform inversion method using combined source encoding.Specifically,the wavelets and seismic data were combined by applying time-shift stacking,and gradients can be determined through only one calculation of reverse time migration.According to the calculation results using a model,the FWI method using combined source encoding can be used to achieve multi-scale inversion and obtain more stable inversion results.Meanwhile,relatively accurate inversion results can be obtained by combining this method with a source-independent method.

With the advantages of flexible configuration,convenience,high efficiency,and resolution,the single-channel seismic detection technology has been widely used in marine geological surveys and offshore engineering geophysical prospecting.However,there are few cases of the application of this technology in inland rivers and lakes.Therefore,an experimental study on the high-resolution single-channel seismic detection technology targeting the inland shallow waters of Baiyangdian Lake,Xiongan New Area,Hebei Province was conducted.The application effects using key acquisition parameters,including excitation energy,excitation interval,sailing speed,and the number of receiving units,were compared to determine the optimal parameter combination.A set of single-channel seismic data processing processes and methods for inland shallow waters were developed to gradually attenuate all kinds of noises and improve the signal-to-noise ratio and resolution to the greatest extent.The experimental results show that the single-channel seismic detection technology for inland shallow waters can finely divide the shallow stratigraphic structure in the waters.Moreover,the division effects agree well with drilling data.Therefore,this technology can effectively support the investigations of environment,geology,and geologic hazards in inland rivers and lakes.

Owing to the small impedance difference with surrounding rock and complex gas-water relationships,it is difficult to identify high-quality reservoirs in block S in the Sulige gas field through the post-stack P-wave impedance inversion.According to the petrophysical analysis of the study area,the pre-stack parameter v_p/v_s ratio can be used to effectively identify lithology and gas-bearing properties.This study firstly determined the seismic response characteristics of the reservoirs through forward modeling.Secondly,it conducted petrophysical modeling and the prediction of shear-wave velocities using the Xu-White model suitable for sandstone and mudstone and accordingly established a petrophysical model.Thirdly,the CRP gathers were optimized using the processing methods such as linear denoising and residual amplitude compensation.Finally,the thickness and gas-bearing properties of the reservoirs in block S in the Sulige gas field were quantitatively predicted through simultaneous pre-stack inversion.The results are as follows.(1)The top boundary of the reservoirs in the study area shows the seismic reflection characterized by strong trough reflection,while the bottom boundary of the reservoirs shows unapparent seismic reflection;(2)The v_p/v_s ratio of less than 1.68 can be used to effectively determine sandstone.This combined with the P-wave impedance of less than 12200 g·cm^-3 ·m·s^-1 can be used to predict the reservoirs in the study area. Moreover, a v_p/v_s of less than 1.57 can be used to identify the gas-bearing properties;(3)Reservoir distribution and the predicted gas-bearing range have similar trends but differ locally.The development degree of reservoirs is not necessarily positively correlated with the gas content.The method proposed in this paper is expected to provide strong technical support for delineating the favorable gas-bearing reservoir area and deploying well locations in the future.

The edge depth of geological body plays a crucial role in the semi-quantitative interpretation of gravity and magnetic potential field exploration. At present, the main inversion methods of geological body edge depth mainly include Werner deconvolution method, analytical signal amplitude method, local wave number method, Tilt-depth method, Euler deconvolution method and curvature attribute inversion method. These methods all have problems of solution selection, stability and adaptability. This paper mainly studies the adaptability of different types of data and models. Through basic principle analysis and model test, the results show that Werner deconvolution method and Euler deconvolution method are applicable to the most types of data sources, followed by curvature attribute, and Tilt-depth is the least; Werner deconvolution method, Euler deconvolution method and curvature attribute methods can adapt to many models, the Tilt-depth is least. For gravity data, the analytical signal amplitude of the first vertical derivative as the data source is applicable to all methods. For magnetic data, the analytical signal amplitude as data source is applicable to all methods. At the same time, it is suggested that other scholars should follow the following principles when using these methods to invert the edge depth of the two-dimensional body: It is recommended that Werner deconvolution is preferred, followed by curvature attribute and Euler deconvolution. The gravity data source of Werner deconvolution method and Euler deconvolution method is recommended to use the horizontal derivative of the first vertical derivative, and the magnetic data source is recommended to use the horizontal derivative. The gravity data source of curvature attribute method is recommended to use the analytical signal amplitude of the first vertical derivative, and the magnetic data source is recommended to use the analytical signal amplitude. In addition, based on the above research conclusions, some suggestions on the future research directions of the solution screening, stability and adaptability of the edge depth inversion are given.

The Laowan area in Henan Province is an important gold minerogenetic area in the Tongbai-Dabie noble nonferrous metal metallogenic belt. Based on the comprehensive analysis of the metallogenic factors of the area, the authors extracted and established nine predictive variables, i.e., strata, ductile shear zones, brittle fault zones, magmatic rocks, gold-related alteration zones, and single-element anomalies of gold, arsenic, antimony, and sliver in stream sediments. Then, the authors predicted metallogenic prospect areas of gold in this area using the weight of evidence model and the MRAS software. Grid cells with a size of 0.10 km×0.10 km were used for prediction, and they were divided into classes A, B, and C in terms of prospecting prediction through the prior probability calculation, weight statistics, independence tests, and posterior probability calculation of each prediction variable. Based on the distribution characteristics of various classes of prediction grid cells and the geological characteristics of gold deposits in the study area, this study delineated four first- and four second-order prospecting target areas. According to comprehensive analysis, most of the known gold deposits or gold ore occurrences fall into the prediction blocks of classes A and B and the prediction blocks of class C lie around the prediction blocks of classes A or B. This analytical result is consistent with the gradual changes of the metallogenic belt from the center to the edges. Gold deposits or ore occurrences have been discovered in all the delineated first-order prospecting target areas, and the posterior probabilities have a high average. Therefore, first-order prospecting target areas have great gold prospecting potential.

Plane beam signals form when multiple excitation sources simultaneously emit pulses with the same center frequency (multiple-source concurrency),thus enhancing the quality of data records.This paper compares and analyzes the electromagnetic wave absorption effects of unsplit recursive convolutional perfectly matched layer (PML) as the absorbing boundary condition and Mur second-order absorbing boundary condition under multi-source concurrency through numerical simulation.According to study results,the traditional Mur second-order absorbing boundary condition did not perform well in absorbing electromagnetic waves under the conditions of multi-source concurrency and multi-angle grazing,and it will cause waveform distortion and spurious reflections in the case of large offsets.For the unsplit recursive convolutional perfectly matched layer as the absorbing boundary condition under multi-source concurrency,coordinate scale factors were introduced into the finite-difference time-domain (FDTD) algorithm.Then,the PML equation for coordinate stretching was transformed from frequency domain into time domain through the inverse Fourier transform.Finally,the electric and magnetic field values were solved using the recursive convolution method in the discrete state,thus avoiding the complicated calculation involved in directly determining the numerical solution of convolution.This allows less memory space and high calculation efficiency while ensuring accuracy.Therefore,the unsplit recursive convolutional perfectly matched layer method improves the electromagnetic wave absorption effect at the positions where the grid terminate without inducing wave-field splitting.

Owing to geographical factors and historical reasons,the urban underground square cavities show increasing number,density,and chaotic state,leading to unclear interpretation results of the ground penetrating radar(GPR) images of these underground square cavities.This study divided the left side of an image(with the symmetry axis as a boundary) of square cavities obtained from the GPR scanning close to the ground into three stages based on the whole process of ground penetrating radar scanning detection.Then,this study established the relationships between horizontal distance and echo delay of each stage.Furthermore,it systematically analyzed the changes in the GPR images of square cavities with different burial depths and sizes.Finally,this study obtained the scientific explanation of geological radar imaging mechanisms of underground square cavities based on GPR detection examples.It is concluded that the three stages of the left side of a GPR scanning image of the underground square cavities in uniform media include a continuous straight line with a constant slope,a monotonically decreasing continuous concave curve,and a continuous horizontal straight line unrelated to the horizontal distance.With an increase in the burial depth and cavity size,the curve tends to be gentle and its open radian tends to increase.

The distortion correction of magnetotelluric sounding curves is critical to magnetotelluric exploration. Based on the comparison between the resistivity logging curves of basin D and the basin's inversed sounding curves before and after being corrected through magnetotelluric sounding translation, this study constructed a transformation function and calibrated magnetotelluric sounding curves using logging curves. The magnetotelluric inversion results improved using the calibration technology proposed in this study are highly consistent with the verification boreholes. Finally, this study effectively revealed the structural characteristics of basin D by combining drilling, seismic, gravitational, and magnetic data.

This study investigates the geochemical characteristics and genesis of selenium (Se) in the soil in Xuancheng City, Anhui Province using the samples of surface and deep soil collected through a 1:250 000 multi-purpose geochemical survey. The results are as follows. The Se content in the surface soil in Xuancheng City is (0.12~8.80)×10^-6, with an average of 0.44×10^-6. Se-sufficient and Se-rich soils are widely distributed in the study area, accounting for 61.90% and 35.63%, respectively. Se-rich soils are mainly distributed in the Ningdun Town in Ningguo City-Fulingtown in Jixi County, Yangong Town in Jingxian County-Baikeshu area in Xuanzhou District, Chencun Village-Chikeng Mountain in Jingxian County, and Xinhang Town in Guangde County. The Se content in the soil is mainly controlled by parent rocks and soil-forming parent materials. Se content is high in soils in the distribution areas of carbonaceous shale and carbonaceous siliceous mudstones, such as the SinianLantian Formation and Cambrian Hetang and Yangliugang formations, as well as Permian, Triassic, Carboniferous, Cambrian, and Ordovician limestone distribution area. In contrast, Se content is low in Yanshanian intermediate-acid intrusive rocks and Quaternary distribution area. In terms of soil-forming parent materials, Se content is higher in soils with parent materials of carbonate, light clastic rocks, and epimetamorphic rocks than that in soils with parent materials of Late Pleistocene loess, alluvium, and acid rocks. In terms of soil type, Se content is higher in limestone soil, skeleton soil, stonysoil, and red soil than paddy soil, yellow-cinnamon soil, and fluvo-aquic soil. Se content in soil is correlated closely with physicochemical indices, such as V, Cd, Ba, Ag, Zn, Mo, U, Ni, Sb, P, S, and organic matter. Meanwhile, total Se content is correlated closely with bioavailable Se content. Furthermore, all the 47 rice samples collected in the study area are rich in selenium, with a selenium accumulation rate of 100%. However, tea and maize are not rich in Se, and some types of vegetables are rich in Se. Therefore, different types of crops have different absorption capacities of Se in the soil.

Gold deposits of the quartz-vein-type are the product of post-magmatic hydrothermal and metamorphic hydrothermal processes and are generally controlled by major and secondary faults. Their metallogenic materials originate from the surrounding rocks. The assemblages and contents of metal sulfides in ores of various deposits differ with geological setting and ore-forming and controlling conditions. Moreover, sulfide-gold-quartz ores predominate. The gold deposits of this type have distinct comprehensive geophysical prospecting features, and various physical prospecting methods yield a high degree of regularity. Taking a gold deposit of the quartz-vein-type in northwest China as an example, this study carried out comprehensive physical prospecting of deposits of this type, performed a quantitative prediction based on forward modeling, and conducted interpretation and analysis by combining theories related to geophysical prospecting.

Anning City, Yunnan Province, China is an important area of economic development and ecological civilization construction in central Yunnan on the upper reaches of the Yangtze River. This study investigated the contents and enrichment degrees of elements including heavy metals in the surface soil samples that were systematically collected in the Anning area from 2018 to 2020. Then, this study assessed the ecological risks of heavy metals in the soil using the geoaccumulation index and the assessment indices of potential ecological risks and analyzed the sources of heavy metals using the methods of the Pearson correlation and principal component analysis. The results show that heavy metals Cr, Zn, As, Cd, Pb, Hg, and radioactive element U in the soil in the study area have significantly higher contents than corresponding background values of soil in Yunnan Province and show high-degree variation and uneven spatial distribution. Moreover, Cr has the highest accumulation degree of geological anomalies, elements As, Cd, and Hg have high potential ecological risks, and ecological risks are mainly concentrated in the phosphate mining area and the vicinity of steel plants and chemical plants in the Tanglangchuan basin. In terms of sources, Cr, Ni, and Cu may mainly originate from soil parent materials; areas with high Cd, Pb, Zn, and As contents are significantly affected by human activities, and Hg may have a composite pollution source. These results will provide a scientific basis for understanding the sources of heavy metals in soil in Anning City and for the management and protection of local land resources.

The requirements for the design and manufacturing of nodal devices are relatively low. The most basic modules of a nodal device include controllers, acquisition circuits, GNSS timing circuits, geophones, batteries, interfaces, downloading cabinets, data downloading & compositing servers, optional testing circuits, signal generators, and QC manuals. As mature supply chains are available for all the above modules, manufacturers pay more attention to organically integrating the above modules into products that can stably work and meet the needs for the signal acquisition of seismic exploration. However, the absence or neglect of some details in some products on the market due to design or cost considerations will cause difficulties in the field application of seismic data acquisition. The data acquisition quality of the nodal devices relies entirely on the independent performance and stability of each nodal device, which further rely entirely on the manufacturers’ understanding of signal acquisition for seismic exploration and data acquisition operations and the resultant design. The requirements of oil and gas exploration and development in new situations must be considered in the design of nodal devices. The focus of oil and gas exploration and development is constantly shifting to deep and ultra-deep parts with more complex ground surfaces, and thus high precision and resolution are required for signal pickup. As a result, nodal devices should be more capable of acquiring weak signals and broadband signals, which cannot be compromised in the design. This paper elaborates on the fundamental details of signal acquisition, test functions, circuit design, storage, batteries, profile, auxiliary systems, quality control, and auxiliary devices in order to avoid problems such as signal distortion, coupling, and EMC.

Quickly and efficiently identifying the hidden dangers inducing ground collapse in cities are greatly significant for urban construction, disaster protection, and protection of people's properties. In this study, the urban shallow ground collapse was classified into cavities caused by dissolution, disorderly drainage of groundwater, and old civil air defense works. Through forward calculations, this study analyzed the response laws of the geological models of the three types of cavities using the opposing-coils transient electromagnetic method (OCTEM), as well as the various characteristics of attenuation curves of the models under high resistance and low resistance overburden strata. Moreover, this study investigated the electrical characteristics of the geological models of the three types of cavities using the rate of change in the transient electromagnetic responses of rocks. The forward results are as follows. Compared with the surrounding rocks, both the models of cavities caused by dissolution and disorderly drainage of groundwater showed low resistance characteristics, while the model of cavities caused by civil air defense works showed high resistance characteristics. The rates of change in the transient electromagnetic responses of the three models show that the opposing-coils technology has a good ability to identify the hidden dangers inducing all kinds of cavities. The application results of the OCTEM to the detection of three types of cavities in areas such as Kunming and Zhengzhou show that this method is effective for the detection of urban shallow cavities.

The "Dongfang No.1" rock mass in the Maping area, Zhenyuan County, Guizhou is the parent rock of a primary diamond-bearing deposit discovered in China for the first time. Studies have shown that the rock mass found in the Maping area is of the shallow facies of the kimberlite magmatic system, and large-scale concealed rock pipes or buckets may exist in the deep part. To reveal the spatial distribution of deep diamond-bearing concealed rock pipes or buckets in the Maping area, this study carried out the audio-magnetotelluric (AMT) data acquisition in the area using a high grid density of 80 m × 40 m. Then it simulated the pure terrain response in the study area using the 3D forward modeling and deducted the pure terrain response from the measured data. The obtained qualitative interpretation results restored the distribution morphology of AMT impedance phase invariants to some extent that was distorted by static effects. Afterward, this study performed the 3D inversion of the data using the AR-QN quasi-Newtonian inversion method. Based on the lithologic statistical results of the study area, the resistivity variation intervals of the underground units were set during the inversion, obtaining a reliable 3D electrical structure. Finally, this study carried out a fine interpretation of the geoelectric model of this area based on geological data such as rock tubes found on the surface and multiple dikes revealed by boreholes, outlining the morphology of concealed rock pipes or buckets. This study will provide a geophysical basis for the future prospecting and prediction of primary diamond deposits in this area.

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.

The transparency of the fully mechanized mining face achieved using advanced exploration equipment and technology can make the information on coal seams more comprehensive and accurate and can lay a solid foundation for the intelligent production of the fully mechanized mining face. DC resistivity method is a common method for geophysical exploration. Owing to the high stability, great anti-interference performance, and sensitive responses to low- and high-resistance bodies, the DC resistivity method is one of the key means of achieving the transparency of the mining face. To explore the application effects of the method in the transparency of the mining face, this study used different working methods to conduct three-dimensional forward and inverse modeling of the response characteristics for solving proven water-bearing structures of the mining face and frontal advanced detection of roadways. The results show that the distribution laws of 3D DC inversion data obtained by corresponding working methods were basically consistent with those of the initial model, and the DC resistivity method can well distinguish between high- and low-resistivity bodies. Therefore, this study can guide the application of the DC resistivity method in the transparency of mining face in practical engineering.

The ultradeep Ordovician limestone fracture-vug reservoirs in the Fuman oilfield on the south bank of the Tahe River in the Tarim Basin is the core target area for the production capacity construction of the oilfield.These reservoirs in the study area contain massive dissolution vugs formed by the formation fracturing due to the strike-slip faulting and thus are highly heterogeneous.The low-frequency models based on conventional wave impedance inversion are built using data on horizons,faults,and logs,and thus they cannot characterize the fault-controlled heterogeneity of the reservoirs.For this reason,this study proposed an iterative inversion method constrained by fault fractured zone facies to predict reservoirs.The technical process of this method is as follows.First,the original seismic data were interpreted to obtain the attribute volumes that can reflect the characteristics of the fault fractured zones of the reservoirs.Then,the attribute volumes were proportionally fused with the initial low-frequency model and the spatial profile data of high-quality reservoirs obtained from the conventional inversion based on wave impedance.As a result,a new heterogeneous low-frequency model was formed.Using this model,multiple rounds of iterative inversions were conducted.The inversion results can truly describe the characteristics of the fault fractured zones in the heterogeneous reservoirs.The prediction results of 10 wells had coincidence rates of up to 92.86%.As indicated by the application,the method proposed in this study can improve the reservoir prediction performance and the prediction precision of fault-controlled reservoirs,thus effectively supporting the work in the study area.

The Baoding sag is located on the western margin of the Jizhong depression,Bohai Bay basin.It is adjacent to the uplift of the Taihang Mountains in the west,with the piedmont fault of the Taihang Mountains as the boundary.Identifying the deep structures and fine-scale geological structure of the sag is greatly significant for the hydrocarbon exploration and the survey and evaluation of deep thermal reservoirs in the sag.Meanwhile,it also facilitates the research on the characteristics of the piedmont fault of the Taihang Mountains.Since the exploration using the seismic reflection method feature high precision and high resolution in the detection of deep geological structure,this study conducted the seismic reflection-based exploration in the tectonic units of the Baoding sag and their periphery.First,high-quality original seismic records were obtained by means of explosive source excitation,long-array multi-channel reception,and high coverage times.Then,seismic reflection sections that can clearly reflect the deep geological structure and structural characteristics of the survey area were obtained using high-precision imaging data processing techniques,such as static correction,pre-stack noise attenuation,deconvolution,and offset stack.The obtained seismic sections allowed for determining the characteristics of faults in the sag and internal secondary tectonic units.Based on the angular unconformities identified in the seismic sections,the basement structural layer and the structural layers formed during the faulting stage and the depression stage of the Baoding sag were also determined,and,accordingly,the tectonic evolutionary process of the three structural layers were discussed.

Laochang, Lancang, Yunnan is one of the most important polymetallic mining areas in the southern part of Sanjiang Tethys metallogenic belt. After years of mining, the shallow resources are nearly exhausted. In recent years, granite porphyry and porphyry polymetallic mineralization have been newly discovered in the deep part of the mining area, highlighting the prospecting potential of deep polymetallic deposits. In order to trace the occurrence of deep ore-controlling strata and structures in the study area and help to make a breakthrough in deep ore prospecting, high-power induced polarization method and audio magnetotelluric method were implemented to image the deep structure situated. Results obtained from the inversion of the measured induced polarization and electromagnetic data recuperated the distribution of induced polarization anomalies and the characteristics of deep electrical structure within the study area. Combined with the available regional geological settings, the main conclusions are as follows: The low resistance and high polarization anomalies in the northwest of the survey area are deeply related to the surface ferromanganese, silver manganese, and deep polymetallic mineralization, and the high resistance and high polarization anomalies in the middle and east of the survey area are in good agreement with the deep polymetallic mineralization. The upper Carboniferous limestone and dolomite strata are thick in the west and thin in the east, with the west strata dipping to SW and the east strata overlying the Yiliu Formation of the lower Carboniferous. The concealed granite porphyry dips in NE direction, and the coupling part between its deep 2 300~2 800 m horizontal section and deep fault is a favorable area for deep polymetallic mineralization. Notably, joint interpretation yielded from the high-power induced polarization method and the audio magnetotelluric method applied improved the reliability of deep polymetallic ore detection and provided more information of positioning the subsequent drilling layout.

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.

In the process of hydraulic fracturing for shale gas extraction, the injection, flowback, retention, and absorption of fracturing fluids will cause changes in electric fields in the case of the excitation by the electromagnetic field from an artificial source in a far area or the excitation by the geoelectric field. The time-dependent change in the information on fracturing can be reflected by monitoring the change in weak electric fields above the hydraulic fracturing area. To meet the needs of the real-time monitoring of the fracturing field, this study focuses on the preliminary study of the monitoring technology based on the nodal acquisition devices of distributed weak electric fields. The monitoring system only collects two horizontally orthogonal electric field signals, monitors the real-time information on the electric field within a certain range, and transmits the preliminarily processed data back to the data center in a wireless way. Test results show that the monitoring system has stable performance, a standby time of more than 10 days, and high sealing performance, and is applicable to complex field environments. Therefore, this monitoring system can provide important technical support for obtaining images of fracturing fluid migration in the future.

The computational efficiency of the forward modeling for gravity and gravity gradient anomalies determines the feasibility of inverse modeling. It also forms the basis for the efficient building of sufficient and diverse deep learning sample data. Inspired by the application of moving-footprint—a fast forward modeling method in the aerospace electromagnetic field and based on the fast space-domain forward modeling of geometric lattice functions of grid points, the authors proposed a computation method for the forward modeling of gravity and gravity gradient anomalies by applying “moving-footprint”, aiming to further improve the speed of the forward calculation for gravity and gravity gradient anomalies. Specifically, this method selects the subspace in a certain effective range directly below an observation point in the underground half-space. The observation point anomaly approximates the total anomalies of the cuboid units in the corresponding subspace while ignoring the anomalies produced by the cuboid units outside the subspace. When the observation point moves, the corresponding subspace moves accordingly. Therefore, the large-scale underground half-space cuboid model can be decomposed into the subspace corresponding to each calculation point for the forward calculation. As shown by the results of a model test, when 32×32×15 subspace was selected in the underground half-space of a 256×256×15 rectangular parallelepiped model for calculation, the relative average error of gravity anomalies and partial gradient anomalies was less than 10% and the calculation speed was increased by 19 times. Moreover, the calculation time of 1024×1024×15 rectangular parallelepiped model is approximately 32 minutes. Compared with the existing algorithms with a bottleneck in the ultra-conventional calculations, the method proposed in this study has significant advantages regarding computation.

The Luzhou shale gas block,which is located in the southern Sichuan Basin,has undergone multi-stage tectonic evolution and has complex faults and multiple sets of vertical detachment layers,forming the characteristics of multiple stages,multiple strikes,and multiple layers.To overcome the difficulties with the tectonic interpretation of the study area,this study combined a set of seismic multi-attribute techniques,namely using seismic multi-attribute optimization and attribute fusion technique to assist fault interpretation,using structural anomaly attribute to identify microstructures,using seismic attribute slicing technique to analyze the characteristics of tectonic temporal and spatial evolution,and using multi-superposition ant tracking attribute technique to predict fracture development.Using this technique combination,this study completed the fine-scale interpretation of complex faults in the area, effectively characterized the development of microstructures,clarified the tectonic stages and distribution in the area,improved the fracture prediction accuracy,and described the development characteristics of fractures.The results of this study will provide solid data and a foundation for the next platform deployment.

In the shallow or mine prospecting using the transient electromagnetic method (TEM), the transmitting magnetic moment is limited by the limited supply voltage of the transmitting system, and the stray inductance of the transmitter loop causes a long turn-off time. To solve these problems, this study designed a parallel transmitter loop of ultra-small coils used in TEM. Using these coils, the transmitting magnetic moment can be increased by the parallel connection of the coils, and the turn-off time can be reduced by additional resistance. The equivalent circuit models of the conventional transmitter coils and the parallel transmitter coils were established and analyzed theoretically. Moreover, the comparative test between the parallel transmitter coils and the conventional transmitter coils were carried out. The results show that the parallel transmitter coils can effectively increase the magnetic moment and reduce the turn-off time. Therefore, this design is greatly significant for reducing the blind area and increasing the prospecting depth in shallow or mine prospecting using TEM.

The forward modeling of wave field response characteristics of wide-azimuth seismic data shows that the reflection coefficient has apparent azimuth anisotropy when the P-waves propagate in underground geologic bodies.It has become a research hotspot at home and abroad to make a fracture prediction using azimuth anisotropy.This study analyzed the response characteristics of the changes in seismic P-waves with azimuth using forward modeling.Based on the analytical results combined with the relationship between the anisotropy parameters of fluid-bearing fractures proposed by Bakulin et al.,this study approximately simplified the Ruger formula,deduced the equation between anisotropic parameter γ that can be used to characterize fracture development and reflection coefficient,and proposed a fracture prediction method based on anisotropic parameter inversion.The validity and applicability of the method have been proven using theoretical models and practical data application.Therefore,this study provides a feasible method and technology for fracture prediction using wide-azimuth prestack seismic data.

The Dashui gold deposit in Maqu County,Gansu Province is a typical mine of the western Qinling region.Owing to continuous mining,many mined-out areas have been formed at different depths below high and steep slopes No.5 and 9,causing local surface collapse and major safety hazards.According to the requirements for environmental protection and safety,there is an urgent need to determine the spatial distribution of concealed collapse to effectively prevent geological disasters.Using the opposing coils transient electromagnetic method (OCTEM),this study conducted the fine-scale interpretation of the anomalies on the typical sections of the exploration area.Based on this,as well as the comprehensive analysis of the hydrogeological data and basic geological data of the exploration area,this study determined the transparent and three-dimensional distribution of the concealed collapse of the Dashui gold deposit.The results of this study show that the subsurface investigation of mined-out areas using the OCTEM can effectively reveal the lithologic and electrical characteristics of concealed strata in mined-out areas.Moreover,the significantly different physical properties between mined-out areas and surrounding rocks can be used to effectively identify the locations and basic morphologies of subsurface mined-out areas.The data on the boundary characteristic points of the mined-out areas on geophysical profiles with multiple exploration lines and three-dimensional modeling allow for the three-dimensional visualization of the spatial morphology of the mined-out areas.The application performance of the OCTEM,along with three-dimensional modeling,provides a technical basis for mine restoration and safety evaluation,thus effectively serving the construction of digital mines.

The Nanjinshan gold deposit is a typical epithermal deposit in Beishan metallogenic belt, which extends in a N-E direction to the peripheral shallow cover zone. In order to further achieve the breakthrough of prospecting in the peripheral shallow overburden area, the pilot work of motorized shallow drilling geochemical survey carried out. Based on the nature and thickness of the overburden, 126 motorized shallow drilling geochemical exploration samples are taken in the shallow overburden area using the vehicle mounted air positive circulation and three wing alloy scraper drilling or pneumatic DTH hammer drilling technology, with a sampling density of 16.8 points per square kilometer. The shallow drilling geochemical exploration methods and technologies in the shallow overburden area are further discussed, including the selection of drilling technology, sampling network, sampling materials, sample collection, etc. Soil survey was carried out in sporadic bedrock areas, and 278 samples were collected, and the sampling density was 48.77 points per square kilometer. Fifteen elements including Au, Ag, as, Sb, Hg, Cu, Pb, Zn, W, Sn, Mo, Bi, Cr, Co and Ni were analyzed. Through the above work, seven comprehensive geochemical anomalies were delineated. After anomaly investigation, six gold deposit bodies and one silver deposit body were found in the new circle in the bedrock area, and two concealed gold deposits and one silver deposit body were found in the shallow overburden area. The results show that shallow drilling geochemical survey is effective and feasible in the shallow overburden area of arid Gobi landscape in Beishan.

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.

The mineralization of deposits of rare metals such as tantalum and niobium in China is mostly related to granite pegmatite. The enrichment of rare metals in these deposits is accompanied by the formation of radioactive minerals, such as albite, monazite, and high-grade uranium, and these deposits have paragenetic and associated minerals uranium deposits. Therefore, radioactive prospecting has become the most convenient and effective method to explore deposits of rare metals such as REEs, Nb, and Ta. Based on the close correlation between mineralization and radioactivity of rare earth minerals, this study fully investigated the parameter characteristics of the surveyed energy spectrum data through the combination of airborne radioactivity measurement and ground gamma spectrometry measurement to determine prospecting indicators. A new niobium-tantalum-rubidium polymetallic mineralized point was discovered in the Nancha area, Yichun City using the radioactive prospecting method, which was thus proven effective.