Grounded-source transient electromagnetic method (TEM) has many advantages such as deep exploration, flexible arrangement in rough terrain and high working efficiency. Recently it has got much attention and a series of new methods are available, ranging from surface to airborne and borehole method. In this paper, the authors review the research history of long-offset TEM (LOTEM), short-offset TEM (SOTEM), multi-channel TEM(MTEM), grounded-source semi-airborne TEM and grounded-source surface to borehole TEM, and summarize their research status in forward modeling, system design, inversion, imaging and field working. The results show that, as a well-developed grounded-source TEM, LOTEM has accumulated many research achievements. Although some progress has been made, the researches on other grounded-source TEMs are still in a primary stage and still need further improvement. Valuable research results in LOTEM, for example, noise suppression technology, high dimensional inversion and point interpretation, can be introduced to these newly developed electromagnetic methods, which can help provide solutions for high working efficiency and high resolution deep exploration.

In the light of the pulse width of the radar wave, this paper deals with the difference and the relationship between the vertical resolution and the transverse resolution of the ground-penetrating radar, indicates the influence of the noise upon the resolution and, with practical examples, points out that the digital handling of the signal can greatly improve the resolution of the radar.

Element abundances of the continental crust and rocks cited in the past and recent literature have been based on compilations of data from various studies. This leads to uncertainties in sample representativeness and data quality. The present study is based on systematic collection of 28 253 individual rock samples over an area of 3.3 million km² in eastern China, east of eastern longitude of 105°.The sampling involves more than 800 igneous intrusive bodies and metamorphic complexes as well as more than 500 type stratigraphic sections. From the individual rock samples, 2 718 composite samples were made and analyzed for 77 elements by 15 specific methods, dominantly XRF and INAA. Analytical quality was controlled by international and national preliminary geochemical reference materials of GSR, GAu and GPt series. Synthetic results from geological, geochemical and geophysical studies were used to construct crustal constitution model, from which element abundances of the continental crust in the North China platform, the upper crust and exposed crust in eastern China, chemical composition of igneous rock in China and of sedimentary rock and metamorphic rock in eastern China were derived.

Dual-Probe Heat-Pulse method was modified for application of determining in-situ thermal conductivity of marine

sediments. It was crucial to process DPHP data and extract thermal conductivity from these data. A processing flow was

established based on measured data with consideration of the specific measurement situations at sea. The pre-processing

procedure, including filtering, trimming, and ambient temperature fitting and eliminating, was suggested in order to obtain a

temperature response curve of heat pulse, which was then utilized to calculate thermal conductivity. Besides the K-B model, a

simplified model to calculate thermal conductivity was advanced which has advantage in reducing operation and cumulative error.

By comparing the two thermal conductivity calculation methods, extremum method and fitting method, it was proposed that the

extremum method will be the first choice so long as the sampling rate was high enough.

This paper has summed up the progress of the ERI method over the past decade of years as well as its future development trend in the following aspects: ① A comparison of the performances of the main ERI instruments used at present shows that the ERI instruments tend to develop in the multi-channel, multi-parameter, multi-functional, high-power direction; ② ERI measurement environment has changed from surface measurement to water surface, underwater and cross-hole measurements, with the last three kinds of measurements analyzed in this paper; ③ On the basis of analyzing ERI data processing method and inverse development status, this paper describes three-dimensional and four-dimensional inversion theory of ERI with practical examples; ④ ERT applications are summed up, and several new applications are introduced. It is concluded that, with the improvement of the probing depth and observation precision as well as the diversification of the observation models, the application field of ERI will become broader and broader, and this technique will surely have wide development prospect.

This paper deals with three gravity satellites, namely CHAMP, GRACE and GOCE. Satellite gravity data are widely used in such fields as the recovery of the earth's gravity field, the land water storage, the study of the geoid change, the elastic thickness, the crustal thickness, the gravity variance before and after earthquake and the crustal movement. Lots of successful and valuable research results were obtained. It is considered that the satellite gravity survey technology is by for superior to traditional gravity survey and will surely have larger application space.

Influenced by the difficulty of exploration and poor seismic quality, the exploration of oil-gas resources in the southwest of Tarim Basin has not achieved a substantial breakthrough after decades of work. Based on the latest high-precision aeromagnetic data obtained in Southwest Tarim Basin in recent years, this paper discusses the geological problems related to oil-gas accumulation, such as basement structure of basin, distribution and characteristics of depressions, main fault structures and their controlling rules for oil-gas migration and accumulation, local anomalies and favorable local structures of oil-gas as well as their distribution characteristics. The results of the study can provide important reference for the further strategic selection of oil-gas exploration and deep resource evaluation in Southwest Tarim Basin.

This study conducted the inversion of the organic matter content in the soil of the black soil area in Sunwu County, Heilongjiang Province using the Sentinel-2A multispectral remote sensing images and the surveyed soil data. After preprocessing the images, the characteristic bands were selected through correlation analysis and using the random forest (RF) method. Subsequently, a multispectral inversion model for the organic matter content of the soil was built using the partial least square method and the BP neural network, and the inversion of the organic matter content of the soil in the Hongqi Forest Farm was conducted. According to the obtained results, the bands selected based on the reciprocal of the logarithm of the first-order differential of reflectance through the correlation analysis and the combined bands selected using the RF method can effectively improve the inversion precision of the organic matter content in the soil, and the RF-BP neural network model for the combined bands yielded the optimal inversion performance (R²=0.7245 and RMSE=1.3127%). The results of this study will provide technical support and reference for the dynamic monitoring of the organic matter content in soils.

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.

In this paper, recent advances in the research and development of quantum magnetometers have been described together with some suggestions on further research work.

The tin-polymetallic mining area of the Yue'e ore district, XiengKhouang Province, Laos, is located in the west of the XiengKhouang Laos-Changshan Vietnam tectonic magmatic belt. Based on the 1:25 000 valley system soil geochemical survey, combined with an analysis of the characteristics of element variation coefficients and concentration coefficients, the correlation of elements, anomaly verification, and gold and other polymetallic ore prospecting potentials, the authors optimized multiple target and prospects areas. The position of the mineralized body was inferred based on geochemical exploration anomalies in key target areas. Through trench verification and drilling engineering verification, good prospecting results were achieved. The area is considered to have copper, tin, lead, zinc, tungsten. It is shown that this method can quickly delineate the prospecting target area and distant scenic area in the thick coverage area and extensive blank research area of Southeast Asian tropical monsoon climate, and can provide an effective basis for the next exploration work.

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.

This paper deals in detail with the basic principles and interpretation techniques forthe detection of underground line pipes with the direct detection mothod.It advances a new vectorintersection drawing method for determining positions and depths of line Pipes and givingconfidence of the detection results.Results with high. confidence can ho provided in situ.Description is also made con-cerning the instrument and equipment for line pipe detection and their application of effects.

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.

After a disposal repository for high-level radioactive waste operates, the near-field surrounding rocks will be long in a thermal-hydrological-mechanical coupling environment. Therefore, their mechanical and permeability characteristics are crucial to the performance evaluation of the disposal repository. The surrounding rocks of the Beishan preselected area for the disposal of high-level radioactive waste in China are typical sparsely fractured granites, whose creep characteristics are directly related to the long-term safety of the disposal repository. Using water jet and wire cutting techniques, along with fracture surface blocking and combined sealing at rock sample ends, this study addressed the challenges of the sample preparation and sealing of fractured granite in thermal-hydrological-mechanical coupling triaxial tests. Based on this, multi-loading triaxial creep tests were conducted. The test results indicate that under the condition of multi-field coupling, the triaxial creep strength of the fractured granite was approximately 80% of its triaxial strength. Creep deformation increased with the axial load level, with lateral creeps more pronounced than axial creeps. For the compacted and crack propagation sections of the rock samples, both the axial strain rate and permeability decreased initially and then increased. In the case of consistent osmotic pressure difference, a higher osmotic water pressure within fractures would lead to decreased peak strength of the rock samples and result in greater lateral creep deformation.The results provide scientific support for the site selection, surrounding rock evaluation, engineering design and construction of the repository.

Based on the analysis of selenium content in soil and agricultural products in the study area, the authors studied the distribution characteristics and influencing factors of total selenium, and analyzed the characteristics of selenium content in agricultural products. The results show that the selenium contents were controlled by the geological background. It was much higher in the Third and Fourth members of Jurassic Nanyuan formation than in other geological background regions.In addition, the contents of selenium in soil under different soil types showed a great difference, and the land use types also has a certain impact on it. The correlation analysis indicates that the selenium content in soil has a significant correlation with pH, organic matter and metal oxides such as TFe₂O₃, indicating that the physicochemical properties of soil play important roles in the geochemical behaviors of selenium. The significant correlation between the selenium content and heavy metals indicates that there is a certain assorted relation between selenium and heavy metals in primary sulfide mineral.

This paper has summed up the development and new application of ground-searching radar in recent years. Based on detailed analysis of the principle and system structure of ground-searching radar, the authors put forward the train of thought for improving system structure of ground-searching radar and, aimed at solving the great noise existing in ground-searching radar work and the inadaptability in transplantation of seismic data-processing technique, raise a new scheme for underground interface high-resolution imaging of ground-searching radar.

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).

The time-lapse resistivity method can be applied to engineering and environmental problems such as monitor groundwater contaminant transport, measure slope stability. In this paper, the normalized data inversion result of the time-lapse resistivity method was used to identify the subsurface structure of small resistivity changes. First, the data ratio normalization was adopted in which the initial data serve as the background data to normalize the data at other times. Next, the separate nonlinear conjugate gradients (NLCG) inversion result of initial data, time-lapse data and normalized time-lapse data were implemented. The same inverted parameters and homogenous half space model that was taken as the reference model were applied in all synthetic data examples. The inversion results show that the normalized data inversion results can effectively distinguish the small changes of resistivity relative to the background, but the conventional resistivity inversion almost cannot recognize it.

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.

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.

This paper makes a generalized description of the scientific and technical advances in magnetic prospecting in China, which include such aspects as gro und magnetic survey, acromagnetic survey, marine magnetic survey, magnetism of rocks, paleomagnetism, absolute measurement of geomagnetic field. data pro cessing and interpretation of magnetic anomalies, and development tendency of this field.

1995 was the last year of China's Eighth Five-Year Plan.Over the past five years,oil and gas geophysical work has developed steadily;techniques such as three-dimensional seism,reservoir description and transverse prediction geophysics have made considerable progress;three-dimensional seismic pre-stack depth offset processing has begun its application;more importance has been attached to direct oil and gas goophysical prospecting technology; some problems such as nonlinear inversion,viscosity and elasticity,double phase and anisotropic media have become focuses of the research.Geophysical work on solid resources has not yet got itself out of the depression;nevertheless,the related techniques remain in progress Our own sofware and hardware system attached to transient electromagnetic method has been basically formed, and gratifying achievements have been acquired in the aspects of distributive type multichannel synchronous electromagnetic system and processing- interpretation working station of integrated electrical method.The increasing market demands for engineering and environmental geophysics have promoted the development of shallow geophysical technique,which,however,still needs the guidance and support from systematic key research projects.

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.

Porphyry copper deposit is the most important copper deposit type in China. With the deepening of mineral exploitation, exploration geochemistry in mineral exploration has become increasingly important. Based on related literature, this paper sums up the exploration geochemical research results of porphyry copper deposits, which include such aspects as geochemical characteristics, exploration methods, anomaly evaluation and prospecting indicators. Exemplified by the Fujiawu copper deposit, this paper reports the latest advances in the study of porphyry copper deposits.

This study aims to systematically assess the pollution risk of heavy metals in the soil-crop-human body system along the periphery of mining areas, thus providing a scientific basis for the classified management of ecological risks and safe crop production in mining areas. Hence, this study examined the soil and crops (rice, corn, and sweet potato) in arable land along the periphery of a typical mercury mining area in Chongqing City. The single-factor pollution index (P_i), Nemero composite index (P_综), and positive matrix factorization (PMF) model were employed to assess the pollution degree and ecological risk of soil heavy metals for source analysis. Moreover, the human health risk assessment model recommended by the United States Environmental Protection Agency (USEPA) was applied to assess the health risks of local staple crops for residents. The results are as follows: (1) The average contents of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn in the soil of the study area were all higher than the topsoil background values of Chongqing and China, suggesting that heavy metals are relatively enriched in topsoil; (2) The single-factor pollution index indicates that the over-limit ratios of Hg and Cd in the soil reached 96.29% and 92.59%, respectively, whereas rice, corn, and sweet potato samples with Cd content exceeding the value specified in the national food safety standard (GB 2762—2022) accounted for 16.67%, 18.75%, and 14.28%, respectively; (3) The Nemero composite index (P_综) was between 1.17 and 46.05, suggesting mild to heavy pollution in the study area, with heavy pollution primarily located around the mercury mining area and artisanal mercury smelters, as well as the lower reaches of the Rongxi River; (4) The PMF model analysis demonstrates that the heavy metals in the soil of the study area originate from three sources: natural source (47.21%), mining activities (16.00%), and a mixed source of mining and agricultural activities (36.79%). Specifically, Cd, Cr, and Ni are principally affected by the natural source, Hg by mining activities, As and Pb by the mixed source of mining and agricultural activities, and Cu and Zn are associated with the natural source and the mixed source of mining and agricultural activities; (5) The human health risk model reveals that the consumption of rice, corn, and sweet potato poses composite health risks for both adults and children. Rice consumption exhibits the highest risk index, especially in children, with the main risk factors being As and Cd.

This paper briefly reviews the history and the overall work deployment of the U.S. National Uranium Resource Evaluation (NURE) program, with emphasis placed on the key techniques of airborne exploration. The airborne exploration included airborne gamma-ray spectrometry (AGRS) and aeromagnetic survey, which collected radiometric and magnetic data over the conterminous United States and Alaska. The airborne program systematically covered each 1° by 2° national topographic map series (NTMS) quadrangles, which were used to locate potential radioactive mineral deposits. The program played an important role in uranium resource and environmental radiation level evaluation, which has far-reaching definition and meaning. The experience and practices of the program should be used for reference. According to the current status of China's survey, top-level design for AGRS should be strengthened. This paper also proposes a national program of AGRS surveys for achieving coverage of terrestrial radioactivity and building a measurement and monitoring system with Chinese characteristics.

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.

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.

The measured gravity anomaly is a superimposed field composed of a regional field and a local field, whose characteristics is complex shape and various amplitude changes. In order to complete the geological task better, it is necessary to separate the regional field and the local field. Based on the the measured gravity anomalies, this paper studies the relationship separately between the elevation and free-air gravity anomaly, simple bouguer gravity anomaly, bouguer gravity anomaly. By the way of mathematical statistics to perform regression analysis, the regional field (background field) and the local field (remaining field) are separated which improves the credibility of the interpretation results of gravity data and provides basic services for analyzing and solving geological tasks.

This study aims to improve the seismic exploration effects in the Upper Paleozoic strata of the Yin'e Basin.With the Juyanhai depression in the western Yin'e Basin as an experimental area,it investigated the previous seismic acquisition characteristics and current data processing techniques of the area.Through field seismic acquisition experiments and data processing research in the laboratory,it explored and summarized the seismic exploration techniques for the Upper Paleozoic strata in the Yin'e Basin.Key findings are as follows:(1)The combination of shot holes and seismic vibrators is recommended for seismic excitation in the area according to local conditions;(2)The receiving array length takes precedence over the receiving density;(3)Targeted processing techniques including anisotropy processing,spectral-constrained deconvolution,and wedge transform adaptive denoising can effectively improve the quality of deep seismic imaging.This study provides a reference for relevant research in similar areas.

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 gold ore zone in the Daduhe area of Shimian County, Sichuan Province, is located in the rare metal-precious metal-nonferrous polymetal metallogenic belt in the southern segment of the Songpan-Ganzi orogenic belt. It exhibits complex structures and steep terrains, severely restricting prospecting and exploration. Based on the geological settings, conditions, and geophysical characteristics for regional mineralization, this study investigated the typical Luoluoping gold deposit in Shimian by conducting deep geophysical exploration centered on audio-frequency magnetotellurics (AMT). Three low-resistivity anomalies (M1, M2, and M3) were identified, corresponding to the mineralized alteration zone I, the gold mineralization zone III, and the gold-copper ore body, respectively, demonstrating the effectiveness and applicability of geophysical methods for deep prospecting. Combined with geological understanding and engineering verification, this study summarized geological and geophysical prospecting markers for the typical gold deposit, establishing the geological-geophysical prospecting model for the gold ore zone in the study area. Therefore, this study provides technical support for deep prospecting in the study area.

In this paper, a simple method for normalization of geochemical data is described. It can be used to reduce the differences between different analytical batches and normalize the data from different areas which have different background values. The method lies in using the ratio of the original analytical value to mean or median value in the batch multiplied by a reference value. The transfer value is given the name apparent content. Two examples are given in this paper to illustrate the details of adjusting the differences.

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.

Effectively identifying the stratigraphic and landslide structures in landslide-prone areas is significant for disaster prevention and mitigation. By investigating the landslides in the Xuelang Mountain scenic spot in Wuxi, this study analyzed the differences between two-and three-dimensional inversion using the high-density resistivity method. Accordingly, this study explored methods for eliminating the banded effect in the three-dimensional inversion, performed three-dimensional resistivity inversion under the constraints of high-precision surface elevation data and borehole-derived prior information, and constructed a three-dimensional geological model for the study area. The results indicate that three-dimensional resistivity inversion enjoys distinct advantages in complex landslide surveys. The banded effect can be effectively suppressed by optimizing the grid spacing, damping coefficient, and filter parameters for inversion. Furthermore, the terrain-induced impacts and the multiplicity of solutions of the inversion can be significantly reduced using constraints of refined terrain data and prior information, thus improving the resolutions of stratigraphic boundaries and landslide structures. Through three-dimensional resistivity inversion and geological modeling, this study determined the three-dimensional stratigraphic structure, along with the spatial distributions of the landslide bodies and sliding surfaces, and investigated landslide mechanisms, providing important data for the survey and control of landslides in the study area.

Ground penetrating radar (GPR) is a high-precision geophysical exploration method whose main purpose is to invert the physical properties of underground structures.In this paper,an improved particle swarm optimization (PSO) is used to solve GPR inverse problem.The inversion takes the signal mean square error as the objective function and uses the finite-difference time-domain method to do forward modeling.In addition,the inversion accuracy is improved by the amplitude compensation of the forward result.Compared with the results based on classical particle swarm optimization inversion method,the algorithm shows considerable improvement in accuracy and efficiency.An analysis of the one-dimensional inversion results of multi-layer simulation data shows that the inversion method is effective for multi-parameter inversion and has good noise immunity.

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.