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 grounded-source short-offset transient electromagnetic (SOTEM) method involves many parameters in field data acquisition. The selection of these parameters is closely associated with the signal quality and detection sensitivity of measured data. Based on the relevant provisions in the organization standard, Technical specification for grounded-source short-offset transient electromagnetic method (T/CGS 002—2021), issued by the Chinese Geophysical Society, numerical emulations, and practical cases, this study analyzed and expounded the selection criteria of critical parameters like transmitting source length, transmitting fundamental frequency, offset, device type, and observation component. The insights obtained in this study are significant for guiding the field construction of the SOTEM device and leveraging its detection performance.

In the context of the goals of both peak carbon dioxide emissions and carbon neutrality, scientific and efficient exploration and exploitation of geothermal resources are criticalfor the geothermal industry. To address the commonly concernedtechnical challenges in the exploration of moderately deep geothermal resources, this study investigated the effectiveness of comprehensive geophysical prospecting in the exploration of geothermal resources inthe Linjiadi area, Aohan Banner, Inner Mongolia. Based on the analysis ofthe geological and hydrogeological conditions, this studypreliminarilyascertainedthe geothermal field characteristicsand the hydrochemicalcharacteristics of groundwater in the Linjiadi area. By comprehensively employingcontrolled source audio-frequency magnetotellurics (CSAMT), CSAMT; microtremor survey; radioactive radon survey; this study roughly determined the distribution of strata, magmatic rocks, and fault structures in the study area, inferring the factors controllinggeothermal anomaly areas and hot-water migration.Accordingly, exploration boreholes were arranged, allowing for drilling verificationwith a total length of 960 m. The results show that the comprehensiveapplication of CSAMT and microtremor survey, combined with radioactive radon survey for auxiliary verification, is effective in exploringmoderately deep geothermal resources. This study will provide a methodological reference for geothermal resource exploration in other areas.

Both the controlled source audio-frequency magnetotellurics (CSAMT) and the microtremor survey exhibit promising application prospectsunder strong urban interference. However,single geophysical inversion methods are challenged by a multiplicity of solutions. To achieve the complementary advantages of different geophysical methods, and address the lateral discontinuity of single-point inversion, this studyexplored the quasi-two-dimensional joint inversion of the CSAMTand microtremor survey data. It enabled the joint inversionby introducing a lateral constraint matrix into the objective function for joint inversion and employing the limited-memory Broyden-Fletcher-Goldfarb-Shanno (LBFGS) algorithm. The reliability and effectiveness of the joint inversion were verified using the inversion example of synthetic data from theoretical models. The results show that compared to single data inversion, the joint inversion can effectively improve the accuracy of inversion results, with the resistivity model more consistent with theshear-wave velocity structure. Moreover,lateral constraints can effectively reduce the discontinuity of the physical parameters of adjacentsurvey points. The quasi-two-dimensional joint inversion with lateral constraints enhances the inversion reliability by obtaining more reasonable profile results of physical parameters and structures with the efficiency of single-point inversion.

Black soil layer thicknesses, anessential attribute of black soil,serves as a significant indicator for measuring the fertility and erosion degree of black soil. Their spatial prediction holds critical significance for supporting China's black land conservation and ensuring food security.Considering the diagnostic characteristics of black soil layers in soil system classification, this study regarded soil layers with organic carbon content higher than 6×10^-3 of soil parent materials as black soil layers.Moreover, it derived the calculation formula for the thicknesses of black soil layers relying on the exponential distribution pattern of organic carbon in the vertical soil profile. Based on the 62 896 topsoil and 15 687 deepsoil organic carbon data obtained from the multi-purpose regional geochemical survey, this study conducted detailed spatial prediction of the thicknesses of black soil layers in the Songliao Plain and analyzed their relationship with soil types and climate factors. Key findings are as follows:(1) The thicknesses of black soil layers in the Songliao Plain range from 0 to 165 cm, with a median of 23.33 cm;(2) The spatial distribution of black soil layers exhibits significant heterogeneity, characterized by thin southwestern and thick northeastern portions;(3) The black soil layers of swampy soil and peat soil manifest the largest average thicknesses between 60 and 80 cm, followed by those of typical black soil (average thickness: 56 cm) and those of albic soil and meadow soil (average thickness: 40~50 cm);(4) The spatial distributions of the thicknesses of black soil layers are closely associated with climatic conditions, primarily showing a significant negative correlation with temperature and a positive correlation with rainfall;(5) The mean annual temperature of 0 ℃ is a significant temperature threshold for the development of thick black soil layers.Above this temperature, the average thickness of black soil layers exceeds 80 cm and no longer changes with temperature. With global warming, the southward shift of this 0 ℃ is otherm may significantly influence the thicknesses of black soil layers.

Thenorthern Laojunmiao gold deposit is located in the southern zone of the Beishan area, Gansu Province, and on the northeastern margin of the Tarim block. It resides in a tectonic environment of the Yaodongliang-Xiaoxigong Paleoproterozoic rift basin. This study delineated five comprehensive anomaly zones in the area through a 1∶10,000 geochemical soil survey. As verified by trenching exploration, three gold ore bodies, one gold-silver ore body, and two low-grade gold ore bodies were identified in the comprehensive anomaly zones, suggesting satisfactory prospecting results. Based on the comprehensive geological and geochemical anomaly characteristics of the deposit, this study established an integrated geological-geochemical prospecting model centering on the HT1 comprehensive anomaly zone. Moreover, it proposed the subsequent prospecting direction, providing a significant reference for the deep and peripheral prospecting in the area.

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.

Unfavorable geobodies such as Karsts, weak soil, and water-rich areas are extensively distributed in China. Under heavy rainfall, they are prone to geologic hazards like collapse. A severe geological collapse occurred in Xiacun Town, Yushui District, Xinyu City, near the Shanghai-Kunming high-speed railway. The space around the collapsed foundation pit was limited, with many interference sources like underground pipelines. With early signals subjected to the mutual inductance effects of receiver and transmitter coils, the conventional transient electromagnetic method exhibited low detection accuracy and anti-interference ability, encountering significant shallow blind zones. To locate unfavorable geobodies in the study area and provide suggestions for the prevention and control of geologic hazards, this study innovatively applied the opposing-coils transient electromagnetic method (OCTEM), supplemented by borehole-based verification. The results show that: (1) The OCTEM exhibited high accuracy, as demonstrated by the high consistency between the geophysical exploration results and the drilling results of the study area; (2) The low-resistivity zone spread across the study area, and the low-resistivity anomalies revealed by geophysical exploration were caused by groundwater according to borehole-based verification; (3) The strata from top to bottom were composed of soft plastic silty clay, hard plastic silty clay, soft plastic silty clay, and moderately weathered limestones; (4) The subsurface micro-confined water in the collapse area surged upward, gradually eroding the soft plastic silty clay layer around the area. The static water level in the collapsed foundation pit manifested an elevation of 55.60 m, located approximately 1.4 m below the surface; (5) A groundwater channel existed under the collapse area, with soil caves formed in the limestone layer under the prolonged erosion effect of water flow; (6) Long-term groundwater extraction may expand the underground seepage zone; (7) The administrative department in charge must promptly contain groundwater in the collapse area to prevent it from further eroding the surrounding unconsolidated soil layer.

Several thermal springs associated with tectonic activity occur along the Chuhe fault zone. Except for the Bantang thermal spring at the southern end, other springs along the fault zone exhibit unideal utilization of thermal energy. This affects the development of local industries. Therefore, it is necessary to delve into the geochemical characteristics and formation mechanism of typical thermal springs along the Chuhe fault zone. The purpose is to provide scientific evidence for the rational utilization and exploration methods of geothermal resources in the thermal spring groups in the future. Therefore, this study investigated thermal springs in the Bantang, Zhaoguan, and Xiangquan areas along the Chuhe fault zone, where nine samples of thermal spring water, cold well water, and surface water were collected individually. For these samples, the composition tests of 25 indices, including anions, cations, and major and trace elements, were tested, and the hydrogen and oxygen isotope values were determined. The analyses of the 25 measured indices, along with the investigation of the geothermal water source and controlling factors through hydrogen and oxygen isotope tracing, indicate that the thermal spring water in the three areas tends to be of the CaSO₄ type and is all closely related to the interactions between groundwater and surrounding rocks. The thermal spring water, cold well water, and surface water in Bantang and Zhaoguan show consanguinity, with geothermal water being directly recharged with local precipitation and surface water. In contrast, the thermal spring water, surface water, and cold well water in the Xiangquan area show weaker consanguinity, indicating different sources for the underground cold water runoff and geothermal water. This should be noted when determining the primary factors controlling the thermal spring in this area. The temperatures calculated using a chalcedony geothermometer were close to the temperatures of the hot water recovered on the surface. In contrast, the temperatures calculated using a quartz geothermometer approached the temperatures of deep geothermal reservoirs. The results of this study preliminarily reveal the geochemical characteristics, recharge relationships, and water-rock interactions of thermal spring water in the Chuhe fault zone and propose effective geochemical geothermometers for the study area. These contribute to deeper insights into the mechanisms and controlling factors of the thermal springs along the fault zone, as well as providing practical value and a methodological model for enhancing thermal spring functionality and geothermal resource exploitation and utilization in the future.

Many cities or urban residential areas in central and western China reside in alluvial plains formed from piedmont alluvial fans. Hence, revealing the stratigraphic architectures and stability of alluvial fans holds critical significance for urban construction planning and rational land use. The alluvial fan in the eastern piedmont of the Liupan Mountains hosts the urban residential areas and villages of Guyuan City, with a dense population. Moreover, the alluvial fan develops several event deposits recording the activity of the alluvial fan under tectonic movements and climatic changes. Through field geological survey, optically stimulated luminescence dating, controlled source audio-frequency magnetotellurics (CSAMT), and conventional radon measurement, this study revealed the stratigraphic architecture of the alluvial fan and its two-phase event deposits (~43.33 ka B.P. and 22.92~20.72 ka B.P) since the Late Pleistocene. As indicated by the CSAMT and conventional radon measurement results, the alluvial fan still exhibits high activity under the influence of the Haiyuan and Qingshuihe faults. The results of this study provide fundamental data for crustal stability assessment, prevention and control of geologic hazards, and engineering construction in the Liupanshan area.

The extensively applied audio magnetotellurics (AMT) has become a primary method for deep geophysical exploration of solid mineral resources. However, its data processing and interpretation often only consider electromagnetic effects but ignore induced polarization (IP) effects, which is inconsistent with actual geological conditions. Based on the two-dimensional AMT finite-element forward modeling with IP effects, this study simulated the magnitude and regularity of the influence of various parameters of IP effects on the two-dimensional forward response. Moreover, this study conducted a numerical simulation on the geoelectric model of sandstone uranium deposits in the Erlian Basin. The results show that: (1) With an increase in the values of polarizability, frequency correlation coefficient, and time constant, the two-dimensional AMT forward modeling with IP effects based on the Cole-Cole model primarily reduced the abnormal response value of two-dimensional forward modeling apparent resistivity and increased the abnormal response value of impedance phase. This is beneficial for detecting low-resistivity targets rather than high-resistivity targets; (2) The zero-frequency resistivity and polarizability in IP effects exhibit a significant influence on the two-dimensional forward response. The influence of both frequency correlation coefficient and time constant on the forward response primarily depends on the polarizability. High polarizability suggests their significant influence on the forward response; (3) In the case of disseminated and sulfide-bearing lithologies in the sand bodies of sandstone uranium deposits, greater IP effects will significantly influence the detection of target sand bodies using frequency-domain AMT. Therefore, forward modeling is necessary before detection to determine the magnitude of IP effects.

The extended spatial autocorrelation (ESPAC)-based microtremor exploration(natural-source surface wave exploration) technology has been extensively used in shallow formation exploration owing to its simplicity,efficiency,and accuracy.However,the imaging effect of dispersion energy extracted based on the ESPAC method is unsatisfactory in practical applications.In particular,different observation array arrangements influence the extraction of dispersion curves from collected data.By investigating the imaging principle of the ESPAC method,this study conducted the simulation experiment of natural-source microtremor recording through ambient noise simulation.It compared the differences in dispersion energy under various dominant frequency distributions of wavelets.Moreover,it quantitatively analyzed the influence of different station arrangements and acquisition durations on the imaging quality of dispersion energy.The comparative study reveals the imaging patterns of the ESPAC method in shallow surface exploration.The ESPAC method can maximize the imaging quality of dispersion energy in the fundamental mode while considering both efficiency and exploration costs.The results of this study were applied to engineering application cases to further verify the simulation results.

The telecontrol electrode array is a new type of electrode array for power supply and observations that utilizes the carrier waves of the power-supply and measurement wires used in conventional electrical prospecting to transmit signals. By remotely controlling a series of coded electrode switches between various wires and their connections, this array allows for orderly power supply and measurements. This array enables flexible spacings between electrodes and the gradual expansion of the distances between power supply electrodes via remote control, thus achieving a gradient-based sounding array. The borrowing-line remote controller can be used combined with single-channel, multi-channel, and high-density resistivity instruments, and the combined arrays can perform 2D/3D electrical prospecting more effectively. Followed by the brief introduction of the principle of the borrowed-line telecontrol electrode array, this study discusses the applications and examples of this array and several combined arrays in the resistivity method and induced polarization (IP).

Over recent years, large-scale geochemical surveys on a scale of 1:25,000 have been conducted in the eastern Kunlun region for geological prospecting. These surveys, characterized by the rapid and accurate location of anomaly sources, have been widely applied in mineral explorations, yielding encouraging mineral prospecting results. Using 1:25,000-scale stream sediment surveys, this study delineated 12 geochemical integrated anomalies of the element associations of Cu, Co, and Ni in the Hedong area, Mangya City, eastern Kunlun. These anomalies include one integrated anomaly dominated by Co, where various element anomalies exhibit high-degree overlap, relatively large scales, high intensity, and distinct concentration zoning. The Co anomaly is closely associated with the Ordovician Qimantag Group, demonstrating a high degree of spatial consistency. The subsequent anomaly verification reveals four cobalt mineralized zones within anomalies GA16, GA26, GA11, and GA39, with three ore bodies and multiple mineralized bodies of cobalt being identified within the mineralized zones. The comprehensive analysis indicates that the eastern Kunlun region enjoys excellent metallogenic geological conditions and favorable geochemical characteristics, with promising prospecting results having been achieved. Therefore, this region has the prospecting potential of medium to large-scale cobalt deposits.

The Mangling ore concentration area with intense magmatic activity has become a focal area for deep prospecting in the North Qinling tectonic belt in recent years. The formation of molybdenum deposits in this area is closely related to small Late Jurassic acidic intrusions. To achieve breakthroughs in deep ore prospection within this area, this study conducted the wide-field electromagnetic sounding over the concealed Yaozhuang intrusion delineated based on gravity anomalies. The results indicate the presence of pronounced high-resistivity anomalies at depth, and it is inferred that the protruding part of the anomalies corresponds to the concealed Yaozhuang intrusion. The resistivity inversion results roughly delineated the variations in the top surface of the intrusion, with the elevations and N-S width of the top surface estimated at -300~620 m and 1300~1600 m, respectively. Drilling in the most favorable deep mineralized part confirmed the presence of the concealed intrusion and concealed molybdenum ore bodies. The results of this study demonstrate that the wide-field electromagnetic sounding method exhibits great sounding depths and high resolutions, serving as an effective method for deep ore prospecting in the Mangling ore concentration area.

In response to the increasing demand for large-scale field seismic acquisition, this study developed a low-cost multifunctional nodal rotational seismometer (RBWL) with a micro-electro-mechanical system (MEMS) sensor, considering the functionality, economic feasibility, and the ease of arrangement. The RBWL employs a low-cost and low-power MEMS sensor to acquire seismic signals, involving three-component translational motions (T_x,T_y,T_z) and three-component rotational motions (R_x,R_y,R_z). To reduce the impacts of environmental factors on measurements, the system of the RBWL automatically records real-time information including temperature and attitude while performing compensation correction on the measurement results. For real-time monitoring and data transmission at acquisition nodes, the system establishes a data transmission link integrating 4G, cloud, and client, with the measured maximum data transmission rate up to 100 Mbps. The testing of H/V spectral ratios verifies the system functions and principal performance parameters of the RBWL and its effectiveness in engineering physical exploration.

Recommendation system algorithms, having recently garnered significant attention in the field of digital Earth science, are expected to be widely applied in metallogenic prediction. Traditional metallogenic prediction studies fail to fully mine the various types of semantic information in massive geoscience data. The deep interest evolution network (DIEN), as a recommendation system algorithm, can fully mine semantic information to predict user preferences. Therefore, this study employed the DIEN model as the prediction model and the semantic information extracted from bedrock interpretation as the ore-controlling elements according to the database provided by the Western Australian government. The model was trained to perform metallogenic prediction for the study area. The prediction results indicate that 92.95% of uranium ore occurrences fell within the medium-high probability zone in the prediction map, with some unknown zones also showing high prediction probabilities. After removing known uranium ore occurrences in some zones, the retrained model still yielded medium-high prediction probabilities in these zones. The results suggest that the DIEN can effectively mine semantic information in metallogenic prediction studies, and the DIEN model exhibits strong predictive capacity for the study area, providing a novel approach for metallogenic prediction studies.

Based on relevant eco-geochemical survey data collected fromthe Lixiahe plain area in Jiangsu Province,this study systematically explored the geochemical characteristics of elements in Se-rich soils and the genetic mechanism through elemental distribution contrast, correlation analysis, R-type cluster analysis, and principal component analysis. This study can be referenced for the rational production and utilization of Se-rich land resources of the Quaternary sedimentary type. Key findings are as follows: (1)Se-rich soilsin the Lixiahe area are typical Quaternary sediments, and the closed lagoon facies sedimentary environment characterized by rich organic matter and slightly reducing conditions plays a foundational role in the formation of local Se-rich soils;(2) Typical element association, Se-OM-N-K-Fe-Co, in Se-rich soils is primarily located within a depth of 30 cm from the surface, with Se content ranging mostly from 0.3×10^-6 to 0.4×10^-6 in a uniform distribution; (3) Significant positive correlations between Se and some other elements can be observed in the soils, with the correlation coefficients (r)between Se and OM,and Se and CEC being 0.74 and 0.66, respectively.In contrast, Se exhibits a significant negative correlation with pH, with a correlation coefficient of -0.35; (4) The formation of Se-rich soilsmight have experienced three Se enrichment stages: the initial enrichment in soil parent materials, the re-enrichment during soil formation, and the supergene enrichment after soil formation, accompanied by interference from non-lagoon facies sediments (such as marine sediments). Organic matter adsorption, colloid adsorption, and biogeochemistry constitute the main causes of Se enrichment in the soils; (5) The Se-rich soils are also relatively enriched in heavy metal elements like Cu, Pb, Zn, Ni, Co, and V, which are within the national limit standards.

Tight sandstones serve as significant oil and gas reservoirs.Their lithofacies identification can assist in further understanding the developmental characteristics of reservoirs.Combining core observations with log data processing,this study analyzed the lithofacies and sedimentary microfacies characteristics of tight sandstones in the Xinchang area and the internal relationships between lithofacies and sedimentary microfacies.Moreover,it constructed a random forest classification model with geological implications through data mining of sedimentary microfacies characteristics.The results show that:(1)Tight sandstones in the Xinchang area can be classified into seven typical lithofacies,including mudstone,siltstone with ripple lamination,massive fine sandstone,fine sandstone with parallel bedding,massive medium- to coarse-grained sandstone,and medium- to coarse-grained sandstone with parallel/cross bedding;(2)The sedimentary microfacies in the Xinchang area consist primarily of subaqueous distributary channel,subaqueous distributary bay,river-mouth bar,and prodeltaic mud,which are closely associated with the sedimentation of lithofacies;(3)In the classification model,the relative centroid(RM),root mean square deviation(GS),average median(AM),and average slope(M) of the gamma ray(GR) curve can be used as the characteristic parameters of sedimentary microfacies to increase the number of characteristics in the dataset;(4)Considering the characteristics of sedimentary microfacies,especially the energy and turbulence of water bodies,can significantly enhance the performance of the random forest classification model.Overall,the results of this study provide a novel approach for lithofacies identification using machine learning methods and a significant reference for oil and gas exploration in tight sandstones.

The Xinzhao gas zone of the Dongsheng gas field resides at the junction of three first-order tectonic units:Yishan slope,Yimeng uplift,and Tianhuan depression.Due to the influence of paleogeomorphology and provenance,different channel sediments vary significantly in this zone.The main target layer is the first member of the Shihezi Formation,which hosts a braided river sedimentary system,with tight reservoirs characterized by typical low porosities and permeabilities.The effective sandstone reservoir exhibits a small thickness,pronounced heterogeneity in gas content,and low-resolution seismic data,complicating sweet spot prediction.Hence,this study delved into the critical seismic prediction techniques for sweet spots in braided-river tight sandstone reservoirs.Firstly,the stratigraphic framework was established based on the three-dimensional seismic relative isochronous surface,characterizing the spatial distributions of channel sand bodies at different stages using the relative-spatial-resolution stratal slicing technique.Then,the seismic data were transformed from the time domain to the frequency domain using the wavelet transform time-frequency analysis technique.Based on the analysis of instantaneous spectrum differences in seismic data of different channels,the qualitative gas content prediction was achieved using the low-frequency energy ratio and the ABV absorption attribute,effectively supporting well deployment.Finally,the facies-controlled geostatistical inversion in the depth domain combining logs and seismic data was conducted for quantitative reservoir prediction, guiding the accurate design and optimization of horizontal well trajectories.The application of these techniques has increased the probability of penetration of gas reservoirs in the study area by seven percentage points, demonstrating satisfactory application effects.

The Rongcheng uplift in North China boasts abundant geothermal resources. Research indicates that the Rongcheng uplift exhibits significantly different physical properties between the bedrock surface and the overlying Cenozoic strata. Moreover, the bedrock surface serves as the primary top boundary of the geothermal reservoir in the Wumishan Formation. Investigating the fine-scale structures, burial depths, and faults of the bedrock surface in the Rongcheng uplift holds critical significance for understanding the distribution and enrichment of geothermal resources in the area and guiding their exploration and production. Through elaborative processing of the north-south reflection seismic profile data of the Rongcheng uplift, collected by the Chinese Academy of Geological Sciences in 2018, this study obtained the high-precision geometric structure of the Rongcheng uplift within a depth of 4 km. The geometric structure was calibrated using geothermal borehole data before interpretation. Key findings are as follows: (1) The Cenozoic sedimentary strata overlying the bedrock surface of the Rongcheng uplift exhibit a nearly horizontal layered distribution, serving as cap rocks of the Rongcheng geothermal field; (2) The bedrock surface of the Rongcheng uplift manifests burial depths ranging from 700 to 3 000 m, with gentle changes in the central portion, and rapidly deepening to around 3 000 m towards the periphery; (3) The Niunan and Rongdong faults converge in the deep part, constituting a fault system along with other medium and small faults, thus facilitating the conduction of water and heat; (4) The geometric structure of the Rongcheng uplift on the bedrock surface contributes to the convergence of heat flow beneath the uplift.

This study performed forward modeling for the short-offset transient electromagnetic (SOTEM) responses of a three-dimensional geoelectric model using the three-dimensional finite-difference time-domain method. The results reveal that: (1) The attenuation curves of the E_x responses from the electric field above the goaf or collapse column were above the background response curve at early times but below it at later times; (2) A shorter offset corresponded to a higher relative anomaly of ∂B_z/∂t response signals. Increasing the length of the transmitting source could enhance the signal intensity while slightly decreasing the relative anomaly; (3) In the case of survey lines close to the transmitting source, the overall ∂B_z/∂t responses of the goaf or collapse column were weaker than the background responses. For survey lines away from the transmitting source, the overall ∂B_z/∂t responses of the goaf or collapse column were stronger than the background responses. In summary, the calculation results demonstrate significant implications for understanding the ability of the SOTEM method to detect typical water-rich bodies in coal mines, laying a theoretical foundation for the parameter selection of SOTEM devices and their generalized application in the coal sector.

The Mianning-Dechang area in western Sichuan serves as the most important metallogenic belt of light rare earth elements (LREEs) in China. To make breakthroughs in the exploration of rare earth resources in the Dechang area, a 1:50 000 stream sediment survey was conducted in this study. The analysis of test data characteristics and the extraction of geochemical anomalies reveal that the total rare-earth oxides (REOs) in the area exhibit a pronounced enrichment pattern and that element anomalies largely overlap the spatial distribution of related geological bodies. Through comprehensive analysis using the cumulative frequency method and iterative method, this study determined the lower limits of anomalies and, accordingly, plotted element anomaly maps, with five main anomaly areas being delineated. The comprehensive evaluation of anomalies revealed four prospecting target areas: Huangjiaba, Jiaobacun, Yibasan, and Huajiaoyuan. The analysis of metallogenic geological conditions and the anomaly verification based on drilling in the Gannan area led to the discovery of three light rare earth deposits in the Huangjiaba prospecting target area, two heavy rare earth deposits in the Jiaobacun prospecting target area, two heavy rare earth deposits in the Yibasan prospecting target area, and two heavy rare earth deposits in the Huajiaoyuan prospecting target area. This study posits that the Triassic biotite moyite and biotite monzogranite in the study area are the metallogenic parent rocks of ion adsorption-type rare earth resources, with REEs primarily undergoing enrichment and mineralization in completely weathered layers. Therefore, a simple and effective prospecting pattern for "endogenous and exogenous" ion adsorption-type rare earth deposits in the Dechang area consists of analyzing the geochemical characteristics of the total REOs based on a 1:50 000 stream sediment survey, delineating metallogenic prospect areas that indicate parent rocks for REE enrichment, and selecting sections favorable for the formation and preservation of weathered crusts based on the hypergenic conditions of the enrichment areas, thus achieving the quick delineation of the prospecting target areas.

Surface waves and guided P-waves,as two boundary-related wave phenomena,are a crucial part of the near-surface seismic wave field.This study investigated their generation mechanism and propagation regularity using the high-order staggered-grid finite-difference algorithm.First,it solved the problems like numerical dispersion and boundary conditions in numerical simulation.Based on this,it designed medium models under different thicknesses and elastic parameters for forward modeling.Furthermore,it extracted dispersion profiles and amplitude versus offset curves for analysis.In the case of a low-velocity thin layer on the surface,guided P-waves can be generated when the phase velocities of P and SV waves from the same source exceed the S-wave velocity but are less than the P-wave velocity of the underlying high-velocity layer.In media with high Poisson's ratios(>0.4),the phase velocities of surface waves and guided P-waves are sensitive to the S- and P-wave velocities,respectively.Surface waves and guided P-waves usually contain near-surface information that is unavailable in refracted and reflected waves.The appropriate acquisition,analysis,and inversion of near-surface information enable the establishment of a high-resolution near-surface model.This study generalized the generation conditions and wave field characteristics of surface waves and guided P-waves under the same source and deepened the understanding of their propagation regularity,laying a foundation for inversion and denoising research.

Based on the combination ofdata- and model-driven approaches, this study expanded the labels of the training set through model inversion results, and added the model inversion objective function to the deep learning algorithm. By constructing a new loss function, this study proposed a seismic impedance optimization inversion method combining model inversion with deep learning inversion. The semi-supervised deep learning network inversion under a pseudo-label was achieved using the RNN network structure. The network inversion results were used as the initial model to participate in the model inversion. The final optimization inversion was completed by continuous iterative optimization of both network and model inversion. The method proposed in this study proves to possess high inversion accuracy and practicability, as demonstrated by the synthesis of the Marmousi model and the actual data.

The Xilin fault zone,intimately associated with gold and polymetallic mineralization,exhibits high potential for gold resources.In deep exploration,identifying the deep structural characteristics of ore-controlling faults plays a critical role in achieving breakthroughs in gold exploration.Through the analysis of gold metallization regularity and the reflection seismic methods,this study clarified the seismic response to the changes in the attitude of the dominant ore-controlling fault zone in the Jiaodong area.It posited that the changes in energy intensity of the seismic event on the seismic time profile,as well as large continuity deterioration zones,can indicate the changes in the fault attitude,demonstrating high mineralization potential.Moreover,this study predicted and verified the metallization targets in the area.

Within a coal mine in Peixian County, Xuzhou City, brick-red Paleogene and Neogene strata were deposited in the faulted basin during the Cenozoic, with extensive Quaternary strata overlying various strata. The Quaternary, Jurassic, and Cretaceous strata exhibit thick overburden, up to over 500 m. This study explored the coal mine using the short-offset transient electromagnetic (SOTEM) method. Based on geoelectric conditions, reasonable observation parameters were designed to obtain the subterranean electric structure within a burial depth of 1500 m. Goafs were detected at a burial depth of 900 m, with their delineated boundaries aligning with the mining situation of the coal mine. The results of this study serve as a reference for detecting goafs with thick overburden in North China-type coalfields.

The Guidong plutonis a crucial part of the EW-directed Dadongshan-Guidong-Wuliting magmatic rock belt in the Nanling region of South China.The Xiazhuang uranium orefield resides in the eastern portion of the Guidong pluton. Researchers have conducted extensive chronological testing on the Guidong pluton, the Xiazhuang uranium orefield, and their veins, obtaining abundant age data. This study synthesized the advances and characteristics of chronological research in the study area. The results show that: (1) The Guidong pluton is a complex pluton formed by Caledonian-Yanshanian magma at 450~151 Ma. From east to west, it can be divided into the Caledonian (450~418 Ma),the Indosinian (246~214 Ma), and the Yanshanian (189~151 Ma) plutons, manifesting a gradually aging pattern from west to east. The Xiazhuang uranium orefield hosts NWW-, NEE-, and NNE-directedmafic veins form eddue to Yanshanian magmatism at 211~91 Ma. These veins can be categorized into five sets according to their ages: 211~185 Ma, ca. 180 Ma, 145~139 Ma, 110~100 Ma, and 93~91 Ma. The uranium mineralization in the orefield lasted from the middle Jurassic to the Miocene with an age of 175~20 Ma, involving five phases and six stages: The Middle Jurassic uranium mineralization (175~162 Ma), the late Jurassic-early Cretaceous uranium mineralization (138~123 Ma, 113~100 Ma),the late Cretaceous uranium mineralization (96~66 Ma),the Paleocene uranium mineralization (65~54 Ma), and the Eocene-Miocene uranium mineralization and modification (52~20 Ma). Among them, 138~123 Ma and 96~54 Ma constituted the primary mineralization epochs. (2) According to the chronological and geological data of the study area,the formation of the Guidong pluton and its uranium mineralization can be divided into the following eight phases and 12 stages. The first phase is the middle-late Caledonian magmatism (450~418Ma),forming subvolcanic and granitic rocks primarily in the northern and eastern peripheries of the Guidong pluton. The second phase is the Indosinian granitic magmatism (246~214 Ma), which was dominated by the granitic magmatism from the middle Triassic to the early stage of the late Triassic.The third phase is the early Yanshanian mafic magmatism and uranium mineralization (211~162 Ma),including three stages: The mafic vein activity from the late stage of the Triassic to the early Jurassic (211~200 Ma), the early Jurassic granitic magmatism(ca.180 Ma), and the middle Jurassic mafic vein activity and uraninite mineralization (179~162 Ma). The fourth phase is the Yanshanian magmatism (163~139 Ma), which formed the Yanshanian pluton in the west of the Guidong pluton, consists of the granitic magmatism during the late stage of the middle Jurassic (163~151 Ma) and the late Jurassic magmatism (145~39 Ma). The fifth phase is the late Yanshanian early Cretaceousuranium mineralization and mafic vein activity (138~100 Ma), which comprises the uranium mineralization at the early stage of the early Cretaceous (138~123 Ma) and the mafic vein activity and uraninite mineralization at the late stage of the early Cretaceous(113~100 Ma). The sixth phase is the late Yanshanian late Cretaceous uranium mineralization and mafic vein activity (96~66 Ma), serving as one primary mineralization phase. The seventh phase is the Himalayan Paleocene uranium mineralization(65~54 Ma).The eighth phase is the Himalayan Eocene-Miocene uranium mineralization and modification(52~20 Ma). 3) The pluton formation and uranium mineralization are relatively concentratedin the study area, such as the Caledonian pluton (450~418 Ma), the Indosinian granitic pluton (238~220 Ma), the Yanshanian pluton (163~151 Ma), mafic vein activity (211~91 Ma), and uranium mineralization (138~123 Ma, 96~54 Ma). There exists a certain time difference between uranium mineralization and granitic pluton formation, indicating that they are non-contemporaneous products. Each uranium mineralization was preceded by mafic vein activity, suggesting an intimate relationship between uranium mineralization and mafic vein activity.

The anisotropy caused by fractures is ubiquitous in formation media.The inversion and prediction of fracture parameters based on anisotropy can somewhat improve the inversion accuracy and prediction reliability of fractures.This study established a reflection coefficient equation based on vertical transverse isotropy(VTI) media.Then,it improved the standard particle swarm optimization algorithm by setting the exit probability based on the Metropolis criterion of the simulated annealing algorithm.Consequently,it obtained the inversion results of compressional- and shear-wave velocities and anisotropy parameters in VTI media.By combining anisotropy-related attributes,Poisson's ratio,and Poisson's velocity, this study predicted the fillers in fractures.The improved algorithm was tested for stability and noise resistance using a two-layer model and a Marmousi2 model,demonstrating its feasibility.Furthermore,the improved algorithm was applied to predict the water-bearing property of fractures using real coal mine data,validating its effectiveness.

The Salt Lake geothermal field in Yuncheng City, Shanxi Province, China lies beneath a densely populated urban area, posing significant challenges to further geothermal exploration and extraction. Based on the distribution of geothermal gradients in the geothermal field, which are higher in the southwest and lower in the northeast, a NE-trending microtremor survey profile was arranged in the southern part of Yuncheng City, aimed at investigating the deep geothermal reservoir structure and NW-trending structures in the geothermal field. The 2D velocity structure profile reveals a pronounced low-velocity anomaly in the eastern part, which is supposed to be induced by the fault fracture zone formed by multiple NW-striking tensional faults. Spatially, this concealed fault zone roughly corresponds to the low-geothermal gradient anomaly in the northeastern Salt Lake geothermal field, suggesting that this fault fracture zone might facilitate the rapid infiltration of cold surface water, thereby lowering the temperature of deep rocks in the northeastern part, leading to the formation of a large-scale low-temperature anomaly zone. Additionally, the faults identified by the microtremor survey can be traceable and confirmed in a controlled source reflection seismic profile in the study area, demonstrating the complementary nature of the two methods. This study further reveals the deep geothermal structures of the Salt Lake geothermal field based on previous efforts. This study provides more valuable bases and guidance for future exploration and resource evaluation of geothermal fields in the region while also demonstrating the effectiveness and superiority of the microtremor survey method in research on urban geothermal resources.

This study conducted magnetotelluric profiling in the Bengbu-Huaibei area of Anhui Province. Combined with gravity and magnetic anomalies, it obtained the deep electrical structure, the distribution of primary strata, and the properties of faults in the area, particularly the morphology of the Xuzhou-Suzhouarcuate nappe structure and the development of deep coal-measure strata. The results indicate that: (1) The Upper Paleozoic strataare primarily distributed under the high-resistivity nappe on the surface of the Xuzhou-Suzhouarcuate nappe structure. Theymanifest low-resistivity and low-densityphysical properties and high continuity, suggesting high exploration potential for coal beneath the nappe structure;(2)On the profile, early-stage faulting was dominated by reverse faults, resulting in local Lower Paleozoic and Proterozoicstrata overlying the Upper Paleozoic strata. In the later stage, normal faults predominated, controlling the Cenozoic deposition;(3) The Xuzhou-Suzhouarcuate nappe structure exhibits a 'high-low' double-layer electrical structure at burial depths shallower than 4 km, withthe dominant thrust fault plane composed of F5 and F6 faults. The leading edge of the high-resistivity nappe on the surface extends northwestward to Xiaoxian County and southward to northern Guzhen County, experiencing significant denudation in the Zhahe area. The above results provide critical geophysical information for the basic geological research and mineral exploration in the study area.

The Galinge iron deposit in Qinghai is overlain by deposits measuring greater than 150 m in thickness. The great burial depths of ore bodies lead to gentle magnetic anomaly morphology, making it difficult to characterize the spatial distribution of ore bodies. Therefore, this study employed three-dimensional magnetic anomaly inversion to determine the three-dimensional distribution characteristics of subsurface magnetic intensity in the study area. Given the prior information of non-magnetic surrounding rocks, the three-dimensional magnetic intensity model clearly presented the spatial distribution of the ore bodies and reflected the presence of intense magnetic bodies at depths of less than 500 m in existing boreholes. Accordingly, it can be inferred that there exist concealed ore bodies at depths exceeding 500 m in the study area. The results of this study suggest that three-dimensional magnetic anomaly inversion can effectively improve target identification, providing clear information on the horizontal positions, depths, and scales of magnetic ore bodies. The proposed inversion method can offer strong support for drilling design and reserve estimation, warranting promotion in detailed exploration of solid minerals.

The method of structural superimposed halo to find blind ore is a new method to find blind ore, which is based on the study of the theory of primary halo to find blind ore-the axial zoning of primary halo, and puts forward two new theories of ‘primary superimposed halo theory’ and ‘structural superimposed halo theory’. The accuracy of blind ore prediction by superimposed halo of structure is determined by the correctness of prediction marks and indexes. Based on the summary of seven common signs of structural superimposed halos in the prediction of deep blind ore deposits in more than 100 hydrothermal deposits, four important quantitative qualitative prediction signs are upgraded to quantitative prediction indicators. The structural superimposed halo prediction signs and indicators of 17 different combinations of accurate prediction of blind ore and discrimination of ore body denudation degree in the deep and periphery of the mining area are described in detail, and a practical ideal model of structural superimposed halo for predicting blind ore and discriminating ore body denudation degree is established. The common prediction signs and indicators of the model have important guiding significance for the prediction of deep blind ore in typical hydrothermal deposits, and have achieved remarkable prospecting results in more than 100 mine applications.

Accurately identifying faults is crucial for the exploration and exploitation of oil and gas fields,and further fault extraction based on this holds critical significance for later comprehensive research.At present,the commonly used fault extraction techniques primarily include automatic fault tracking,fault slice interpretation,and manual interpretation.However,these fault extraction techniques and their application in practical exploration and exploitation often face the following challenges.Automatic fault tracking based on an attribute volume often extracts faults with low accuracy and poor continuity,whereas fault slice interpretation and conventional manual interpretation require long work cycles.Hence,this study proposed a fault extraction technique based on structure-oriented filtering.First,the original poststack seismic data were processed through structure-oriented filtering to improve the quality of fundamental data and enhance the fault boundary features.Then,a relative isochronous model was established based on the filtered data volume,with sensitive attributes that can characterize faults extracted.Finally,based on the analysis of fault combination relationships,a comprehensive interpretation method combining plane and profile views was employed to extract faults.The technique proposed in this study has been successfully applied to a certain block of SB.As indicated by the application results,the proposed technique exhibits higher reliability,accuracy,and efficiency compared to the three commonly used fault extraction techniques, thus demonstrating high applicability.

A variogram serves as a crucial tool for quantifying spatial correlations. However, existing variogram fitting methods often yield unstable results. This study proposed an automatic variogram fitting method based on deep learning, aiming to enhance the precision and stability of automatic fitting. The fitting of the experimental variogram is essentially a nonlinear optimization problem, which involves optimizing the matching between the experimental and theoretical variograms. The proposed method generated substantial training datasets using several sets of theoretical variograms with varying parameter values for training and learning in deep neural networks. The trained model was then used for the automatic fitting of the experimental variogram. Multiple sets of experimental results demonstrate that based on the robust fitting capability of deep neural networks, the proposed method manifested superior fitting stability and computational efficiency compared to the least squares method, providing a novel approach for automatic variogram fitting in geostatistics.

The transform from transient electromagnetic (TEM) field to pseudo wavefield is the basis for using the imaging technique. The TEM field follows the diffusion equation, while the pseudo wavefield follows the wave equation. These two can be transformed into each other via the Q-transform. As the integral transformation from TEM field to pseudo wavefield is ill-posed, numerical method is used to get the desired pseudo wavefield. As a result, it is often the case that the methods and parameters are need to be optimized to get a optimal pseudo wavefield. Therefore, here in this paper, we derived the analytical solution of the pseudo wavefield from the TEM field. We start from the analytical formula of TEM field, and utilize the Laplace transform to establish the analytical solution pairs. The pairs can be used to test the accuracy and stability of the numerical method, as well as examining the features of the pseudo wavefield to get an effective imaging method.

The fault-controlled fractured-vuggy carbonate reservoirs in the Tarim Basin exhibitconsiderable burial depths, complex structures, and highly developed faults. Faults serve asa dominant factor controlling oil and gas accumulation and possible hydrocarbon migration pathways in the study area. Hence, it is critical to predict their spatial distributions and sizes. There existvariousfault detection attributes, which characterize fault scales and features differently due totheir different calculation methods.Moreover, conventional attribute detection ignores the use and constraints of logs. For more complete and accurate fault prediction results, this study selected multiple fault detection attributes for fusion using the feedforward neural network algorithm, with logs as prior information. First of all, a sample database for fault feature identification was established using fault attributes (like AFE, likelihood, and dip angle) with distinct characteristics anddiscrimination criteria of fault types, including lost circulation data, imaging logs, and seismic event dislocations.The deep feedforward neural network was trained based on the sample database.A neural network prediction model with a minimum prediction error was obtained by comparing and testing the learning effects under different hidden layer depths. Finally, the neural network prediction model was applied to the fault prediction of the study area. The comparative analysis reveals thatthe fault prediction using deeplearning-based fused attributesyielded prediction results more consistent with the log-based interpretation results, and could synthesize the information of faults with different scale characteristics, thus effectively improving the prediction accuracy and reliability.

In shallow engineering investigations, the small-loop transient electromagnetic (TEM) system is challenged by limitations such as overweight equipment, significant transmitter-receiver mutual inductance, and high manpower requirements. Hence, this study introduced an improved system. Based on the opposing-coils transient electromagnetic (OCTEM) theory, this study calculated the magnetic field distribution of the generalized opposing-coils antenna device. Furthermore, it designed and developed efficient portable antennas and the supporting system (collectively referred to as the portable OCTEM system). Subsequent field experiments demonstrate that while ensuring exploration accuracy, the portable OCTEM system can enhance the investigation efficiency by effectively mitigating the transmitter-receiver mutual inductance and significantly reducing manpower requirements. This study preliminarily verifies the feasibility of the portable OCTEM system, providing a novel technology route for developing downsized shallow exploration equipment.

Non-destructive testing of the internal structural characteristics of ancient buildings is the key to preserving cultural relics.To determine the structures and internal defects of the ancient Great Wall in Linhai City,this study performed non-destructive testing of the wall structures in different orientations using a ground-penetrating radar (GPR) combining 100 MHz and 270 MHz antennas.The testing results show significant structural stratification in the ancient Great Wall.The GPR signal-reflected images reveal clear internal wall defects like pores,cracks,voids,and other hidden dangers.This study demonstrates the reliability of the GPR in detecting structures and defects of ancient walls,there by providing technical support for the structural protection of the ancient Great Wall.

The accurate lithologyidentification of volcanic rocksserves as a significant foundation for the efficient exploration and exploitation of volcanic reservoirs. However, volcanic reservoirs exhibit intricate lithologies, longitudinalmultistagesuperimposition, and fast transverse phase transition, which reduce the accuracy of crossplots in lithologyidentification ofvolcanic reservoirs. Based on the optimal parameter combination of the model determined through grid search and orthogonal experiments, this study quantitatively evaluatedthe effects of conventional log curves on the lithologyidentification of volcanic rocks. Withthe natural gamma ray, compensated neutron, sonic interval transit time, and formation resistivity as lithologic indicators, this study builtan intelligent model for the lithology identification of Carboniferous volcanic rocks in the Dixi area in the Junggar Basin using therandom forest method. This study identified the lithologies of thecored intervalswith a cumulative thickness of 870 m infive cored wells in the study area, with the coincidence ratesof the identification results with thin section identification results and core description resultsreaching 76.67% and 85.98%, respectively. This suggestssignificant identification effects. Therefore, this studysets the stagefor the fine-scale evaluation of volcanic reservoirs in the study area.

The environmental capacity of lake sediments serves as a significant indicator for assessing the environmental carrying capacity of lake systems, effectively reflecting the stability and sustainability of lake systems.This study investigated the Dongping Lake in the lower reaches of the Yellow River basin by determining 11 heavy metal elements, including As, Cd, Cr, Co, Cu, Hg, Mn, Ni, Pb, Tl, and Zn, in the sampled surface sediments. It delved into the spatial distributions of heavy metal contents and environmental carrying capacity using statistical analysis and geographical information system (GIS) technology. Moreover, it predicted the trend of environmental capacity changes of heavy metals at a centennial scale. The results indicate that: (1) The maximum content of As in the surface sediments of the study area exceededits risk screening value (allowable limit) for soil contamination, whereas those of other elements were below corresponding allowable limits;(2) The average single environmental capacity index (P_i) values of heavy metal elements decreased in the order of Hg, Pb, Cr, Ni, Zn, Cd, Cu, Co, Mn, Tl, and As. Among these heavy metal elements, As displayed overload level and warning level points, whereas Mn and Tl manifested warning level points. The composite capacity index (P_i) was calculated to be between medium and high capacity levels. The composite capacity level measured based on the inferior level of P_i suggests a medium capacity to overload level distribution in the study area;(3) The static annual capacity limits of heavy metal elements decreased in the order of Mn, Zn, Cr, Ni, Cu, Pb, As, Co, Tl, Cd, and Hg, whereas the dynamic annual capacity limits decreased in the order of Mn, Zn, Cr, Ni, Pb, Cu, Co, As, Hg, Cd, and Tl. The static and dynamic capacity limits will show a steeply to gently decreasing trend in the 5~40 years and 5~15 years, respectively, followed by a gentle and stable trend. Regardless of the number of years, the average dynamic annual capacity limit is higher than the average static one, suggesting a high environmental carrying capacity.This study reveals the current status and future trends of environmental capacity in the Dongping Lake, providing a scientific basis for the environmental quality assessment and ecological conservation and restoration of the lake.

For the underground construction of coastal cities in China, there is an urgent need to accurately position unfavorable geobodies such as faults and boulders. Based on the geological characteristics of coastal cities, this study conducted 3D numerical simulations using a high-density resistivity method, determining the effects of the electrical properties and thickness of the overburden on the survey results, as well as the DC electric field characteristics varying with the sizes and burial depths of detection targets. The results show that the resistivity difference between the overburden and the targets serves as a critical factor in determining the influence of the overburden. For low-resistivity fracture zones, a higher resistivity of the overburden signifies more prominent responses from the fracture zone. Under middle- to high-resistivity overburden conditions, shallowly buried boulders can be easily found, and larger boulders exhibit more significant high-resistivity characteristics. In the exploration along the Qingdao metro line 5, the high-density resistivity method played a vital role in exploring fracture zones and boulders, verifying the effective application effects of the method. The results of this study provide a basis for selecting engineering exploration methods and determining operating parameters in coastal cities.

Due to dense buildings and structures and insufficient drilling surveys, the construction of shield tunnels passing through urban karst formations that host dense buildings faces significant risks of surface fracturing and subsidence caused by karst development. Hence, this study employed the microtremor survey technology with strong anti-interference capability in complex environments to address this challenge. Based on the technology, it analyzed the structural characteristics of wave velocities in underground rock formations through the inversion of the apparent shear-wave velocity profile. Combined with geological drilling data, it inferred the bedrock interface, highly weathered unconsolidated formations, and karst cave anomaly zones. Key findings are as follows: (1) The apparent shear-wave velocities in the study area gradually increased from the shallow to deep formations. Formations with wave velocities above and below 300 m/s were inferred to be limestone and Quaternary formations, respectively, with the rock-soil interface at depths approximately between 10~15 m; (2) Seven low-value anomaly zones of apparent shear-wave velocities ranging from 150~240 m/s were interpreted. They were presumed to be unconsolidated formations or karst caves at depths ranging from 8~30 m. Relying on strong anti-interference and high accuracy, the microtremor survey technology can accurately identify the shear-wave velocity structures of underground profiles, lithologic interfaces of formations, unconsolidated formations, and karst cave anomalies. Therefore, the technology is effective in the geological exploration of urban dense building areas with karst development.

Surface-related multiple elimination(SRME) is vital in processing seismic data.At present,the SRME method most commonly used for processing marine data can effectively predict surface-related multiple models,achieving multiple elimination through matching and subtraction.However,this method requires full wave field information,thus placing higher demands on observation systems.The irregular land data acquisition makes it difficult to apply this method for processing land data.Hence,this study presented an improved SRME method,which performs moveout correction on adjacent channels for multiple prediction by constructing the minimum error constraint function,thus enhancing the adaptability to complex observation systems.The improved SRME method was applied to process the actual seismic data of land.Its effectiveness was validated by comparing the gathers,velocity spectra,prestack time migration profiles,and synthetic seismograms before and after SRME.

Tunnel detection in complex environments requires fine-scale detection of small unfavorable geobodies like karst caves and fissures. Hence, this study designed a tunnel construction model with a small karst cave in front of the tunnel face. A borehole was drilled at the center point of the tunnel face towards the construction direction, and then an electrical source was put into the borehole for excitation. Array data acquisition was conducted on the tunnel face. The 3D forward modeling based on transient electromagnetic data was performed using the time-domain finite element method. As indicated by the results, the electromagnetic sounding of the target was achieved through the movement of the electrical source, and the planar position of the unfavorable geobody was determined based on the distribution patterns of the electromagnetic field on the tunnel face. Therefore, electrical source excitation in a borehole can enhance the detection ability of the transient electromagnetic method on small karst caves, serving as a feasible method for improving the accuracy of tunnel seismic prediction.

To investigate thehydrochemical characteristics of shallow groundwater in a chemical industrial agglomeration area in Yantai City, this study collected 12 sets of groundwater samples and one set of surface water samples from the study area and its surrounding areas. It analyzed the hydrochemical characteristics ofgroundwater by integrating various methods like mathematical statistics, Piper and Gibbsdiagrams, correlation analysis,the ion ratio method, and principal component analysis. Moreover, it explored the impacts of production activities in thestudy area on the groundwater environment. The results show that:(1) The shallow groundwater in the study area was neutral to slightly alkaline, with the primary hydrochemical type being the SO₄-Ca·Na type, followed by the SO₄·HCO₃-Ca·Mg, HCO₃·SO₄-Ca·Na, SO₄·HCO₃·Cl-Ca·Na, SO₄·Cl-Ca, SO₄·HCO₃-Ca, and SO₄-Na types;(2) The chemical composition of shallow groundwater originated principally from the combined effects of evaporite and silicate dissolution; (3) Chemical enterprises contributed significantly to groundwater contamination. A nearercontamination source is associated with higher ion concentrations,suggesting more severe groundwater contamination. Along the groundwater flow direction, contaminants in upper reaches are prone to migrate and accumulate toward lower reaches,aggravating groundwater contamination in lower reaches.

The Autonomous Underwater Vehicle (AUV) equipped with a magnetometer conducts underwater magnetic anomaly detection, enabling long-duration and large-scale continuous sampling. It offers advantages such as concealment, high efficiency, high practicality, wide application range, strong maneuverability, and robust endurance. To improve measurement accuracy, synchronous seabed magnetic field data is needed as a reference to counteract environmental magnetic noise. To address this, a submarine optically pumped magnetometer was developed to provide a reference for processing AUV magnetic anomaly detection data.The submarine optically pumped magnetometer consists of a magnetic field measurement unit and an acoustic release unit, capable of high-precision autonomous acquisition of the total magnetic field on the seabed, as well as underwater acoustic release and recovery. The magnetic field measurement unit includes an optical pumping probe, electronic unit, counter, battery pack, and nylon pressure chamber. The acoustic release unit includes an acoustic transducer, acoustic communication board, electro-corrosion decoupler, cement block, buoyancy block, and frame. This design addresses key technical challenges such as miniaturization, autonomous acquisition, and underwater acoustic communication.In 2022, a magnetic anomaly detection test was conducted in the offshore waters of Qingdao. The test results verified the autonomous seabed magnetic field acquisition and the release and recovery functions of the submarine optically pumped magnetometer, providing effective reference data for underwater target detection.

Marine controlled-source electromagnetics (MCSEM) is used to explore resources such as oil and gas hydrates, as well as deep geological structures, by revealing resistivity differences below the seabed. Different excitation frequencies correspond to varying detection depths. To enhance the resistivity imaging of targets beneath the seabed, this study investigated the MCSEM-based technology for generating arbitrary-frequency waveforms to flexibly alter the excitation frequency and improve the exploration effectiveness and efficiency. Using the direct digital frequency synthesis (DDS) chip AD9833 and the joint control of a microcontroller and a complex programmable logic device (CPLD), this study achieved the generation of arbitrary-frequency waveforms with limited precision. The test results indicate that this technology can effectively enhance the spectral adaptability and flexibility of MCSEM.

Water and soil erosion affects the distribution and partitioning of elements in soils. The distribution and partitioning patterns and bioavailability of trace beneficial elements such as selenium (Se) and zinc (Zn) in water and soil erosion areas serve as significant factors for measuring the ecological effects of water and soil erosion. Through the geochemical survey of soil and crops, this study investigated the geochemical characteristics and bioavailability of Se and Zn in the water and soil erosion area of Changting County, Fujian Province, obtaining the critical geochemical parameters of Se and Zn in soil and crops in the study area. The results are as follows: (1) The soil Se and Zn contents in the study area show median values of 0.43×10^-6 and 46×10^-6, respectively; (2) Se is enriched in the soil developed from metamorphic rocks, whereas Zn is enriched in the soil developed from metamorphic rocks and granites; (3) The soil Se and Zn contents are higher in bamboo forests compared to other land-use types; (4) The soil Se content shows a decreasing trend as the water and soil erosion intensifies; (5) The bio-concentration factors of Se and Zn are significantly positively correlated with w(Si)/w(Al) ratios, and negatively correlated with Se, Zn, and organic matter. As indicated by the results above, the distribution and partitioning of soil trace beneficial elements like Se and Zn in the study area are primarily subjected to metamorphic rocks and granites. The water and soil erosion is accompanied by a significant soil Se loss. The bioavailability of soil Se and Zn is reduced by the adsorption of clay minerals and organic matter. Additionally, there may be a large proportion of inactive Se and Zn in the soil of the water and soil erosion area.

Seismic data processing reveals that internal multiples exhibit highly complex formation mechanisms,making their accurate identification and effective suppression a persistent challenge in geophysical exploration.Traditional methods for internal multiple suppression frequently require manual identification of subsurface reflection interfaces,making them difficult to apply to complex underground medium structures.Moreover,these methods are not only computationally cumbersome but also typically ensure only temporal and positional consistency when predicting internal multiples.The amplitude often deviates from observed values,requiring adaptive matching subtraction algorithms for effective suppression.This study developed an internal multiple suppression method based on Marchenko theory.Specifically,the wavefield relationships between the focusing function and Green’s function were constructed using the convolution and correlation reciprocity theorem of the Green’s function during data processing.The Green’s function was then solved using the focusing function,yielding either multiples or primaries constructed from the Green’s function.This method requires only the background velocity or the original data as operators during the iterative multidimensional correlation and convolution process,rendering it simple and computationally efficient. This study constructed an expression for the primary wave field using the Green’s function and the Marchenko equation.The tests using the SMAART model and actual data from the Gulf of Mexico demonstrate that the Marchenko method can effectively suppress internal multiples under the conditions of complex subsurface media.The iterative process requires no velocity information,providing significant advantages over conventional methods and great potential for application in complex underground environments where layers are difficult to distinguish.