Low-density geochemical mapping is characterized by high order streams to be sampled and a large coverage area and can be used to effectively trace geochemical blocks with high metal contents. Based on the 1:1,000,000 low-density geochemical mapping data of Ethiopia and the processing of the testing data of Cu in the original stream sediments, this study calculated the anomaly threshold of Cu at 37×10^-6 through iterative deletion. Then, this study delineated three geochemical blocks and two regional anomalies with 37×10^-6, 42×10^-6, 47×10^-6, 52×10^-6, 59×10^-6, and 66×10^-6 as grading intervals. It calculated the mineralization coefficient of Cu ore bodies in the study area at 0.055% by referencing the known reserves of Cu deposits in geochemical blocks with a high level of copper exploration in the same metallogenic belt. Moreover, this study estimated the Cu resources in the study area at 2,600,000 t based on a rock mass thickness of 1,000 m. By combining the analysis of metallogenic geological conditions, this study determined that the zones where geochemical blocks nos. 2, 3, and 4 are located can be considered key metallogenic prospect areas for further detailed exploration.

Due to the lack of effective deep exploration techniques, it has become a key and difficult task to expand the scale of prospecting by obtaining the mineralization information in the deep and peripheral areas of the proven typical deposits of the Huijiabao anticline in southwestern Guizhou. To truly reflect the characteristics of deep geological anomalies, this study investigated the deep ore-bearing Longtan Formation of the Zhexiang gold deposit in the eastern Huijiabao anticline. The information on deep Au anomalies was extracted through geochemical exploration in boreholes of any azimuth according to the profiles, longitudinal profiles, and deep 3D planes of survey lines. Then this study summarized the distribution patterns of geochemical anomalies and evaluated the deep metallogenic potential of the Zhexiang gold deposit. The geochemical data obtained from deep boreholes were processed using the iterative histogram method and the sample length weighted average grade method, respectively. The results show that the Longtan Formation in the mining area had Au anomaly background values of (0.04~0.12)×10^-6 and an anomaly threshold of about 0.24×10^-6. As revealed by the anomaly contour maps generated from the processed data using the above two methods, the distribution characteristics of Au anomalies are in high agreement with those of deep ore bodies, and the distribution ranges of high Au anomalies in all profiles are highly consistent with the morphologies of the proved ore-bearing zones (bodies). Moreover, the large-scale and unclosed high Au anomalies follow the dip direction of fault F₂₀ in the first member of the Longtan Formation. The 3D distribution of Au anomalies shows that the nearly EW-directed high anomaly zone in the central mining area is consistent with the axial region of the Huijiapu anticline. As indicated by the analysis of the multi-dimensional geochemical anomalies and the geological characteristics of the study area, fault F₂₀ is the main ore transmitting and controlling fault in the mining area, and the northern and eastern deep parts around the mining area have great metallogenic and prospecting potential. In addition, two prospecting targets were delineated, needing further engineering verification. This study plays an important demonstration role in guiding the exploration of other mining areas in the Huijiabao anticline. The feasible study methods can be referenced for the study of geochemical anomalies in other mining areas.

In order to clarify the prospecting direction and achieve a breakthrough, 1:10 000 soil geochemical survey and natural heavy sand survey were carried out in Kundelezalag area, and the geochemical characteristics of 10 elements such as tungsten, tin, lead and zinc in the soil and the heavy mineral characteristics of natural heavy sand were preliminarily summarized. Correlation analysis is used to analyze the symbiotic combination of elements. The geochemical elements in the area are Pb-Zn-Ag-Cu and Sn-W-Mo-Bi, in which Sn is the most enriched and differentiated, and the peak value of Sn content is more than 300×10^-6。 23 kinds of heavy minerals, such as cassiterite, garnet, ilmenite and zircon, were identified through natural heavy sand survey, and the genesis of tin polymetallic deposits in the mining area was preliminarily identified through the combination characteristics of heavy minerals, cassiterite extension coefficient and geological characteristics. Finally, according to the geochemical characteristics of elements, the distribution and combination characteristics of cassiterite and the metallogenic clues found in the anomaly area, the Cu-W polymetallic prospecting prediction area and Cu-Zn-Sn-W polymetallic prospecting prediction area in the south of Kundli-Zarage are selected.

Previous studies of associated elements of the No. 510 uranium deposit in Sichuan mostly focus on individual ore blocks. To classify the types of associated resources in the whole deposit, this study conducted a comprehensive comparative analysis based on the investigation of horizontal and vertical zoning of associated elements of uranium ores, as well as the existing study results of rock and deposit geochemistry and metallogenic regularity. Accordingly, this study ascertained the zoning characteristics of associated minerals in the whole deposit. In the vertical direction, the deposit was divided into three mineral assemblage zones: the iron-nickel sulfide-uranium mineralization zone, the low-content sulfide-uranium mineralization zone, and the sphalerite-low-content iron-nickel sulfide-uranium mineralization zone. In the horizontal direction, the deposit was divided into the upper Ni, V → Zn → Ni (low-content Cu) and the lower Mo, Ni, Zn, V → Zn, Ni → Mo, Ni, Zn → Zn (low-content Cu) metallogenic element assemblage transition zones. The smelting and recovery experiments were completed for uranium and associated metals such as molybdenum, nickel, and zinc in the deposit, increasing the economic value of the deposit and expanding economic benefits. This study determined six types of associated resources for the No. 510 uranium deposit and comprehensively evaluated the utilization of associated elements, providing theoretical guidance for both the deep prospecting prediction and the prospecting of replacement resources in similar mines.

The Niuxingba plumbum-zinc-gold-silver deposit (the Niuxingba deposit) occurs in the Yinkeng ore field at the intersection of the EW-trending Nanling metallogenic belt and the NNE-striking Wuyishan metallogenic belt. It is a typical hydrothermal vein deposit under the strict control of fault structures, with ore bodies occurring as vein groups. To predict the deep prospecting potential of the No. V31 major ore belt (body) of the Niuxingba deposit, this study systematically investigated the axial (vertical), transverse, and longitudinal geochemical characteristics and zoning of tectonic primary halos of the ore belt (body) based on the geological characteristics of the deposit. Then, this study determined the axial zoning sequence and the geological-geochemical model of tectonic primary halos. It was confirmed that this model was correct, reasonable, and reliable using the multivariate statistical method. The results of the geological-geochemical model show that: ① the front halo of the Niuxingba deposit has F as the indicator element; ② the near-ore halo has two types of indicator elements: the gold mineralization-related As-Au element association in the middle and upper parts of the ore body and the Pb-Zn-Ag mineralization-related Hg-Zn-Pb-Ag-Cu-Bi-Sb element association in the middle part of the ore body; ③ the rear halo has the Mo-Cr-Co-Ni element association as indicator elements; ④ the anomaly centers of the front, near-ore, and rear halos are about 200~300 m apart axially, suggesting significant coexistence of front and rear halos and the presence of inflection points of the near-ore halo broken line. Furthermore, the transformation of low-moderate-temperature Pb-Zn-Ag-Au mineralization into moderate-high-temperature Cu-Zn mineralization occurs eastward. These characteristics indicate that the No. V31 main ore belt (body) has a pitch direction of east and a large extension toward the deep part (to an elevation of -200 m at least), implying that blind ore bodies may occur. As verified by deep drilling in the eastern concealed area (the lowest ore-controlled elevation of the No. 367 survey line: -165 m), the eastern deep part of the No. V31 ore belt (body) has a high potential for increasing reserves.

The Tonglvshan ore field is the most important skarn copper-iron-gold polymetallic ore field in the southeastern Hubei ore concentration area. Since its mineralization is closely related to Tonglvshan stocks, ascertaining the deep distribution and morphologies of these stocks and their contact relationship with surrounding limestones and marbles holds great significance for deep prospecting prediction of the ore field. This study first conducted a detailed analysis of the gravity and magnetic anomaly combinations of the Tonglvshan pluton and stocks; limestones and marbles, as well as their xenoliths; and skarn ore bodies and mineralized bodies. Accordingly, this study inferred the boundary of the Tonglvshan pluton and delineated the xenoliths and mineralized bodies of limestones and marbles within the Tonglvshan pluton. Then, this study conducted the 3D geological modeling based on the results from the 3D physical property inversion and 2.5D and 3D gravity-magnetic human-computer interaction inversion, as well as the drilling and geological data. Finally, this study established a 3D geological model for the plutons and mineralized bodies at depths of 4000 m and below in the Tonglvshan ore field, providing a basis for target delineation and deep prospecting prediction.

Southern Ningxia, located in a typical loess tableland area, hosts five semi-concealed - semi-exposed faults as boundaries of tectonic units. Based on the regional geotectonic conditions and outcrops, this study analyzed the distribution of the geophysical anomaly field in the study area, ascertained the distribution morphology of the concealed fault sections and the relationship between the faults, and established the fault framework in southern Ningxia. Based on the 1:200000 regional gravity and aeromagnetic data, this study extracted the weak signals of deep gravity and magnetic anomalies reflecting faults using both the multi-scale wavelet decomposition technique and the boundary recognition method and compared these signals with the deep faults depicted based on MT profiles. The results show that the five major faults in the study area are the boundaries of the significant gravity high anomaly zones in the detailed second-order wavelet field of gravity. The Niushoushan-Luoshan-Kongtongshan fault is the boundary between the north-south-trending long strip-shaped gravity anomalies and the north-west-trending flaky and banded gravity anomalies. This fault has typical dextral strike-slip characteristics and is the boundary fault between the Alxa microcontinent and the Ordos block. The Haiyuan fault is divided into Haiyuan faults Nos. 1 and 2 at depth. The No. 1 Haiyuan fault is concealed in the Haiyuan Basin and does not exhibit gravity anomalies. Moreover, the aeromagnetic anomaly field of this fault has significant zoning characteristics. The No. 2 Haiyuan fault is exposed at the northeastern feet of the northern and southern Mount Huashan and exhibits distinct characteristics of linear gravity anomalies but weak aeromagnetic anomalies. The two faults jointly constitute the composite boundary between the Early Paleozoic North Qilian Orogenic Belt and the Alxa microcontinent. Three faults in the Alxa microcontinent, namely the Tianjingshan fault, the Yantongshan-Yaoshan fault, and the fault at the eastern piedmont of Luoshan, are present as the northeastern boundary of the arcuate high-amplitude gravity anomaly zone.

Xiong'an New Area has great potential for geothermal resources. Carbonate rocks are favorable reservoirs for deep geothermal resources in this area. The integrated geophysical exploration technology is an effective way to ascertain the deep structures and the characteristic stratigraphic structure of carbonate geothermal reservoirs. Aiming at the exploration target of deep carbonate geothermal reservoirs, this study put forward a surface-line-point hierarchical and progressive geophysical exploration model. Using the high-precision gravity and aeromagnetic data, this model first investigated the distribution range of carbonate rocks, the thickness of carbonate strata, the distribution of deep-seated faults, and the fluctuation of bedrocks. Then, it analyzed the low-resistivity anomalies of geothermal reservoir strata using the magnetotelluric method. Finally, this model finely characterized the geothermal reservoir strata using two-dimensional seismic profiles and analyzed the velocity structure and regional structural characteristics of anomaly zones in the geothermal field. Based on the exploration precision and reliability of gravity, aeromagnetic, magnetotelluric, and seismic geophysical methods in the geothermal resource exploration of different stages, as well as other factors such as construction cost and efficiency, this study analyzed the economic applicability of geophysical methods in the exploration of deep karst geothermal reservoirs and suggested that the carbonate geothermal resources should be explored using the geophysical exploration technology combination of gravity, magnetic, and magnetotelluric methods.

Crust-mantle velocity structures,which provide an important basis for research on deep structures and dynamic mechanisms,are primarily determined using seismic tomography.A high-quality and fine-scale velocity reference model can provide an effective initial model and constraints for seismic tomography.However,existing methods for building a crust-mantle velocity reference model suffer some shortcomings,such as the lack of fine-scale building of the surface model and the partial distortion of the crust-mantle model caused by vertical global correction.To overcome these shortcomings,this study proposed an improved method for building a 3D crust-mantle velocity reference model.Firstly,the optimal Moho and sedimentary basement models were selected and constructed.Then,these boundary models were used to constrain and adjust the crust and upper mantle models vertically,including the linear correction and weighted fusion through partial compression and stretching.As a result,a crust-mantle medium model was established.Subsequently,the surface model was built in combination with prior geological data.Finally,these models were combined to construct a 3D crust-mantle velocity reference model.Using this method,this study built a 3D crust-mantle S-wave velocity reference model for the central South China Block by collecting previous crust-mantle structure models and geological data of the block.The comparative analysis shows that the model built in this study enjoys higher resolution and more accurate regional Moho,thus verifying the effectiveness of the method.This study provides a reliable 3D velocity reference model for the central South China Block.

Owing to the poor physical properties,the tight reservoirs in the Jimusaer Sag can yield industrial oil flow only through hydraulic fracturing.The research on mechanical properties and the brittleness assessment of rocks can provide a certain reference for hydraulic fracturing.This study obtained the mechanical properties of the tight strata in the Jimusaer sag using triaxial mechanical tests and determined the log parameters potentially sensitive to rock brittleness by analyzing the correlation between the sensitivity of the brittleness index and logs.Then,based on the grey correlation theory,this study determined the initial sequence of sensitivity parameters and normalized the parameters selected.Then,it quantitatively correlated the selected parameters with the potential sensitivity to the brittleness index and determined the degrees of correlation and their order.On this basis,this study established a matrix for the pair-wise comparison of the sensitivity parameters using the analytic hierarchy process (AHP) and determined the weight vector.Then,it established the functional relationship model between the brittleness index and the sensitivity parameters,thus developing a new prediction model for the brittleness index.Finally,this study compared the log models with the brittleness model established based on mechanical properties and the brittleness index determined through laboratory tests.The study results are as follows.The tight strata in the Jimusaer Sag have high brittleness,and the comprehensive brittleness index characterized using the whole-process stress-strain curve agreed with the actual brittleness characteristics of rocks.The degree of correlation of the sensitivity parameters determined using the grey correlation method was in the order of natural gamma-ray(GR)>resistivity(R_t)>density(ρ)>neutron(CNL)>sonic interval transit time(ΔT),which had a weight coefficient of 0.33,0.22,0.18,0.16, and 0.11,respectively in the new prediction model.The prediction method proposed in this study was applied to the Lucaogou Formation in the Jimusaer Sag.Compared with that determined through laboratory tests,the brittleness index predicted can reflect the actual brittleness of the formation,exhibiting a high consistency.As shown by the results from well tests,the productivity index of oil was proportional to the brittleness index,and a higher brittleness index was associated a high production capacity after fracturing.Therefore,the new method provides a new approach to brittleness index prediction and guides the parameter selection for the fracturing of reservoirs.

Located in the loess tableland area,the eastern Ordos Basin features criss-cross ravines and gullies and great topographic fluctuations.Its complex surface conditions and near-surface structures caused significantly different amplitudes,frequencies,and phases in the original seismic data of different regions.These differences are unrelated to the subsurface geological information and can easily lead to misinterpretation.Therefore,there is an urgent need to develop a processing method for seismic data consistency according to the characteristics of seismic data in the study area,aiming to improve the fidelity of seismic data.Based on the summary of the current consistency processing methods,this study built a new consistency processing flow for seismic data under complex surface conditions.By innovating surface consistent amplitude compensation,this study employed the dual-domain near-surface Q-absorption compensation for the first time to broaden the frequency band and improve the amplitude and frequency consistency of seismic data collected across gullies and tablelands.In addition,this study applied the surface consistent deconvolution of Yu's wavelet to attenuate the low-frequency noise and broaden the effective signal frequency band,improving the signal-to-noise ratio,resolution,and wavelet consistency of seismic data.The actual application verifies that the method used in this study is feasible and effective and has a high popularization value.

Time-frequency analysis (TFA) has been widely used in seismic exploration,thus it is crucial to develop a TFA algorithm with high time-frequency resolution.Given the limitations of conventional TFA methods,this study proposed a TFA method based on the regularization theory.The proposed method considers the signal in a short-time window as a superposition of harmonics with different frequencies and takes the TFA problem as an inverse problem.From this perspective,the TFA problem is ill-posed and needs to be solved based on the regularization theory to get a significant time-frequency spectrum.The solution methods under the conditions of L₁ and L₂ norm constraints and the minimum support constraint are commonly used in the regularization theory.This study investigated these solution methods and unified them into the same solution framework.Numerical analysis shows that the TFA method under the condition of the minimum support constraint yielded high time-frequency resolution.This method was systematically applied to the actual data of a specific study area,producing a time-frequency data volume with high time-frequency resolution.Moreover,the planar reservoir distribution was clearly characterized using a single-frequency data volume,demonstrating the promising application prospect of the method.

To further explore the influence patterns of side anomalies in resistivity-based advance detection for roadways and to improve the detection accuracy,this study conducted three-dimensional forward modeling using an adaptive unstructured finite element method based on dual weighted posteriori error estimation.First,this study verified the applicability and accuracy of this method in the simulation of advanced detection using an infinite vertical plate model.Then,it established a model without considering side anomalies to simulate the advance detection response in roadways.Then,it conducted numerical simulations of high- and low-resistivity side anomalies' directions,the distances from side anomalies to roadways and mining faces,roadway sizes,power supply and reception ways,and the influence of side anomalies on advance detection in multi-layer media.Finally,this study analyzed the morphological characteristics of apparent resistivity anomaly curves.The results are as follows:(1)The actual positions of anomalies in front of roadways can be inferred from the extreme values of anomaly curves;(2)The responses of high- and low-resistivity side anomalies generally do not mask the response characteristics of anomalies in front of roadways.However,they can distort the anomaly curves in the corresponding range by making them convex or concave,with the distortion positions consistent with the actual positions of anomalies;(3)The presence of roadway cavities enhances the responses of anomalies on roadway floors.Although different roadway sizes impose different effects on anomalies on roadway rooves,they do not affect the responses of anomalies in front of roadways in general;(4)In multi-layer strata,anomaly response curves can still reflect the actual positions of side anomalies.Whether the response characteristics of anomalies in front of roadways are masked depends on the resistivity of each layer;(5)The identification of interference anomalies requires further research in combination with actual conditions.

Particle swarm optimization algorithm has many advantages compared with linear inversion algorithm in magnetotelluric sounding inversion.However, the standard particle swarm algorithm also suffers from premature maturity in multidimensional optimization problems.Therefore, an optimized particle swarm algorithm based on the Lévy flight randomized wandering strategy is used to escape the local optimal solution,The results show that compared with the standard particle swarm optimization algorithm, the optimized particle swarm algorithm has faster fitness decline and better optimization ability.Finally, the improved particle swarm optimization algorithm is applied to the measured data of known boreholes, and the results show that the algorithm has good practicability.

This study investigated the fine inversion of the broadband magnetotelluric (BMT) data of the Mandulatu area in the Erlian Basin, aiming to improve the inversion precision and performance of BMT data and to provide an example and reference for the fine inversion of BMT data of other areas. For the fine inversion of BMT data of the study area, this study selected the OCCAM inversion method and the TM+TE data mode. The inversion accuracy of data was effectively improved when the two-dimensional moving average resistivity model was selected as the background model, the regularization factor was set to 0.4, and the thickness of the first layer was set to 40 m. This result laid a basis for the subsequent fine interpretation of data. As shown by the results of this study, the key to reducing the multiplicity of solutions and obtaining reliable inversion precision and performance of data is to conduct an adaptive experimental study of the inversion methods, data modes, and parameters first using prior information, such as known borehole or seismic data.

The plain area in Pinggu is a major groundwater source for Beijing.To ascertain the spatio-temporal distribution of groundwater in the study area without damaging the strata,this study,using the non-intrusive time-lapse resistivity method,conducted the reciprocal measurements with Wenner and dipole-dipole arrays in Beiyangjiaqiao Village,Pinggu District.The least-squares inversion results of the profile observation data and normalized data show that:(1)the phreatic and confined aquifers in the study area are approximately horizontally stratified,with the phreatic aquifer being recharged from the north and flowing from north to south;(2)during the entire observation period,the phreatic aquifer showed a drop in water level and leakage into the confined aquifer below;(3)the water content in the aeration zone increased from April 24,2021 to September 12,2021.In contrast,the water content in the confined aquifer remained relatively stable in this period,without experiencing significant changes.The results of this study lay the foundation for the subsequent research on Quaternary strata and groundwater in the study area.Moreover,they can be used as an important reference for the development,management,and utilization of groundwater in the study area and provide a new philosophy for research on the dynamic process of groundwater.

As an inevitable physical phenomenon in the application of frequency-domain electromagnetics, the static shift effect is generally suppressed or eliminated by correction. This study proposed a new approach of directly utilizing the static shift effect of natural electromagnetic methods to explore shallow electrical anomalies. The frequency selection method of telluric electricity field (FSM) is to study the variations in electrical properties of subsurface media by measuring several horizontal electric field components with different frequencies generated on the surface by the natural alternating electromagnetic field. In this study, the forward modeling of FSM data was conducted using the two-dimensional finite element method. The modeling results are shown as follows: (1) In the case of low-resistivity anomalies near the surface, the curves of horizontal electric field components along the survey line on the surface showed the same morphologies as the FSM-derived curves, with significant low-potential anomalies above the low-resistivity anomalies; (2) As the calculated frequencies increased, both the profile curves and the pseudosection map of electric field components exhibited a static shift effect, indicating that the FSM-derived anomalies were mainly caused by the static shift effect. Both the FSM application results and the drilling verification results showed that with the presence of groundwater, the FSM-derived profile curves and pseudosection map exhibited a significant static shift effect, which was consistent with the CSAMT exploration results. As indicated by theoretical and practical research, it is feasible to directly use the components of the telluric electricity field for the exploration of shallow electrical anomalies. Moreover, shallow geological exploration can be conducted by utilizing the static shift effect of the frequency domain electromagnetics.

Three-water(free water,microcapillary water,and clay water) models are widely used in the interpretation of clastic reservoirs.However,these models involve many parameters,some of which are difficult to determine.The methods for determining these parameters are mostly based on the statistics of a large amount of experimental data in study areas.To solve the multi-parameter problem in the application of three-water models,this study proposed a new method to calculate the cation exchange capacity based on the complex resistivity data.Accordingly,it built a new three-water model.Then,it determined the parameter values of the three-water model using nuclear magnetic resonance (NMR) data combined with the optimal genetic algorithm.The resistivity of the completely water-saturated rock samples calculated from these parameters had a relative error of 0.3417 compared to the resistivity obtained from experimental measurements.The method proposed in this study is simple and easy to use.Moreover,this method does not rely on too many experimental data but requires only complex resistivity and NMR experimental data.Therefore,this method can be used as a reference for determining the parameters of new three-water models of other areas.

To ensure the transverse continuity of the inversion results of central loop transient electromagnetic (TEM) data, it is practical to combine multiple survey points into a whole by applying transverse constraints and to establish correlations between adjacent survey points. This study employed the constraints of weighted transverse and vertical roughness to improve the correlations between adjacent survey points and thus to improve the inversion accuracy. Furthermore, this study introduced the adaptive regularization factor, which was obtained adaptively by calculating the norms of the data and the model objective functions in each iteration. In this manner, the dependence on the initial model can be reduced. Finally, using the algorithm developed, this study conducted the inversion of the measured data and data from three-dimensional forward modeling based on the unstructured time-domain finite element method. The inversion results are consistent with the actual results, indicating that the proposed algorithm in this study can enhance the continuity of the inversion results and has a high anti-noise ability.

The one-dimensional inversion of induced polarization (IP) sounding data involves multi-parameter nonlinear optimization. This study achieved the one-dimensional (1D) inversion of IP sounding data based on the improved global optimization algorithm of differential evolution (DE) with two-step mutation. The conventional DE algorithm includes mutation (single-step), crossover, and selection operations. The two-step mutation method proposed in this study can produce new individuals through the mutation of the optimal individual and two randomly selected individuals in steps, thus enhancing the influence of the optimal individual and the global optimization ability. The model test results show that the two-step mutation method has a higher optimization ability than the conventional method. Specifically, the polarizability parameters were loaded using the equivalent resistivity method, and the surface IP sounding resistivity curves of a layered model can be quickly calculated through forward modeling using the digital filtering algorithm. Based on this, the DE algorithm with two-step mutation was employed to produce new individuals through continuous mutation. Then, the resistivity obtained through forward modeling was fitted with the observed values, and the individuals whose fitness approached the maximum fitness were selected as the inversion results. The inversion method proposed in this study features simple operations and fast calculations. As verified through the calculations of H- and KH-type geoelectric models, the inversion method enjoys high fitting accuracy.

This study synthesized microtremor signals using the normal mode superposition.The dispersion curves of the synthesized microtremor signals were calculated using the spatial autocorrelation method,and the calculated results agreed well with theoretical dispersion curves.The simulation of microtremor signals involves many parameters,which are of great significance for microtremor exploration.As shown by results from numerical experiments of these parameters,the hypocentral distance and array size had a significant influence on the results.Moreover,high-order surface waves should be considered for complex strata,while small-size arrays tended to yield high-frequency dispersion information at quiet observation sites,thus improving the resolution of shallow strata.Therefore,it is necessary to consider the influences of hypocenter distribution,array size,and high-order surface waves on exploration results in microtremor exploration.

Hydraulic fracturing is required during the exploitation and stimulation of hot dry rock (HDR) reservoirs.The stimulated reservoir volume (SRV) is the main criterion for evaluating the hydraulic fracturing performance.As a technical link of hydraulic fracturing,Microseismic monitoring can be used to effectively estimate the SRV.This study explored the calculational method of SRV based on the microseismic continuous fracture network model with the purpose of guiding the hydraulic fracturing of HDRs.First,the continuous fracture network was modeled based on the temporal and spatial distribution and multiple source parameters of microseismic events.Second,the fracture grid length was extracted and the appropriate fracture height and width were selected to calculate the SRV.Last,the method proposed in this study was applied to the dual-well HDR microseismic monitoring data.The application results show that this method can effectively estimate the SRV,thus providing a basis for the subsequent exploitation and stimulation of HDRs.

As shown by appraisal wells in structure A in Panyu District, the actual trap geometry differs significantly from its pre-drilling understanding. The analysis shows that the difference is mainly caused by the velocity anomalies in the middle-shallow layers. Breaking through the conventional methods for velocity modeling and correction, this study proposed a new method for velocity correction and variable velocity mapping suitable for the target area. In this method, the causes of velocity anomalies were analyzed based on well data, and then the velocity anomalies were ingeniously combined with seismic amplitude. Accordingly, the trend surface with geological significance for velocity anomaly correction and corrected interval velocities were obtained. The resulting depth-structure map with errors of less than 5 m effectively presented the trap geometry. This study provides a certain reference for the subsequent ascertainment of structures in the same geological setting.

As important urban facilities,underground pipelines perform the functions of energy transfer and information transmission,providing convenience and guarantee for urban life.Ground-penetrating radar (GPR),as a high-resolution,high-precision,trenchless,and non-destructive detection technique,has great advantages in pipeline surveys.However,undulating surfaces with complex terrain greatly influence GPR-based detection of underground pipelines.Therefore,this study conducted numerical simulations of the underground pipeline detection using the finite element method,which can be combined with an unstructured grid to fit the undulating surfaces effectively.Furthermore,this study introduced the height correction method to match the obtained geologic sections with terrain,making it easier to analyze the anomaly characteristics.Finally,through numerical experiments,this study analyzed the influence of undulating surfaces on the detection of pipelines with different burial depths,spacings,materials,and fillers,providing a theoretical basis for GPR data interpretation.The experimental results show that waveforms and reflected wave energy,subjected to distortion due to surface undulations,cannot be used as the sloebasis for judging pipeline information.Therefore,height correction is required,and the vertexes of hyperbolas can be used to judge the burial depths and materials of pipelines.

High-precision aeromagnetic surveys have been carried out in the Qihe-Yucheng area, Shandong Province in different years. To effectively reuse the existent survey data, it is necessary to merge them to form large-scale high-precision aeromagnetic data. This study processed the aeromagnetic data acquired in 2011 and 2017 through correction, continuation, and combination. Then, these data were merged using methods including tie-line leveling, weak magnetic data leveling, and micro-leveling. As a result, 1:25,000 high-precision aeromagnetic data were obtained, with a survey grid spacing of 250±16.2 m and total precision of 1.3 nT. The new data had higher resolution and contain richer geophysical information. This study fills the gap of 1:25,000 aeromagnetic data of the study area and provides important basic data for subsequent data processing and interpretation of the study area.

To ensure the high quality of data acquisition in high-precision ground magnetic surveys in the field, it is an important link to ascertain the instrument performance in a period using instrument calibration points. However, some workers fail to properly use instrument calibration points and thus fail to monitor the operation state of instruments on a day through the early and late calibration measurement of the instruments, affecting the acquisition of high-precision magnetic survey data. Based on the analysis of specific examples, this study proposed that the checking of early and late calibration measurement results of instruments should consider both the differences between these results, as well as the differences between these results and the actual magnetic field values of instrument correction points. The purpose is to ensure the high-quality field acquisition of high-precision magnetic survey data.

Exploring concealed deposits in covered areas is an important way to solve the current resource dilemma. Extensive experimental studies using the deep-penetration geochemical methods developed at home and abroad have been conducted targeting some known concealed deposits, yielding satisfactory results. However, these methods have yet to be widely employed for prospecting in unknown covered areas due to the failure in determining whether surface metal element anomalies are directly from deep ore bodies. Accordingly, it is urgent to develop a tracing technique for surface anomalies. The Shuiyindong gold deposit in Guizhou Province is a super-large fully-concealed Carlin-type gold deposit in China, and its ore-forming fluids are rich in elements such as S, Au, As, Sb, and Hg. This study sampled surface fine-grained soils in the Shuiyindong gold deposit for the concentration analysis of five trace elements (Au, As, Cu, Sb, and Hg), verifying the prospecting effect of the total metal measurement technique of fine-grained soils in this deposit. Moreover, the source of surface soil anomalies was identified using sulfur (S) and lead (Pb) isotopes. This study found that: ① The total metal measurement technique of fine-grained soils showed encouraging indicative effects, with the high Au-As-Sb-Hg anomalies obtained roughly consistent with the distribution of concealed ore bodies and faults, and Hg exhibited the best indication effect on concealed ore bodies. ② The δ³⁴S values and the ratios of radiogenic w(²⁰⁷Pb)/w(²⁰⁴Pb) and w(²⁰⁶Pb)/w(²⁰⁴Pb) in the soil above concealed ore bodies and faults were significantly higher than those in the soil of the surrounding rock area, effectively indicating that the anomalies in the surface fine-grained soils were from deep concealed ore bodies. This study provides a theoretical basis for exploring concealed Carlin-type gold deposits in the same type of covered areas using the total metal measurement technique of fine-grained soils.

This study integrated the data of both the multi-purpose regional geochemical survey and land quality geochemical survey covering an area of 33 092 km² in eastern Qinghai. Based on these data, the total organic carbon storage of topsoil in the study area was estimated to be 171.16 Mt, with an average organic carbon density of 5 172.14 t/km². Moreover, this study analyzed the spatial distribution and main influencing factors of organic carbon in topsoil. As indicated by the results, the average density of organic carbon in topsoil is significantly high in high and middle-low mountains, grassland and meadow soils, soil parent materials of eluvial-slope deposits, forest grasslands, and alpine sparse vegetation areas, grassland and forest and is the lowest in deserts, aeolian sandy soil, and soil parent material areas of aeolian sands. This finding means that factors including topography (altitude), soil parent materials, climate, and vegetation affect the density and distribution of organic carbon in topsoil. Compared with the organic carbon storage revealed by the second general detailed soil survey in Qinghai, 53.21 Mt of organic carbon has been released from the topsoil of eastern Qinghai in the past 20 years. This result indicates that the soil organic carbon has decreased to a certain extent under the influence of human production activities such as long-term cultivation, overcutting, and overgrazing.

The heavy metal pollution in cultivated land is a hot and key issue, and the pollution status and mechanisms can be accurately grasped through small-scale ecological risk surveys of heavy metals in soil. In this study, the heavy metal ecological risk survey of cultivated land and major crops was carried out in Yancang and Lushan towns, Weining County, Guizhou Province. Meanwhile, the pollution status and ecological risks of heavy metals in soil were assessed using the geoaccumulation index and the potential ecological risk index proposed by Hakanson. The results are as follows. The compound pollution of heavy metals exists in the soil of the cultivated land, with Cd showing the highest pollution level and ecological risks. Meanwhile, Cd exceeds the standard in some potato and maize samples, which is closely related towater-soluble and exchangeable Cd. Therefore, more attention should be paid to the studies on the pollution and speciation of heavy metals in the monitoring and remediation of soil pollution in cultivated land in the future.

The development of Se-rich land has been carried out in many regions of China, achieving remarkable results. However, no Se-rich land or crop has been reported in Tibet. This study analyzed the characteristics and influencing factors of the Se content in the soils and crops of the key arable land areas in Bailang County, Tibet, aiming to lend support to the development and utilization of Se-rich land in the Qinghai-Tibet Plateau. The results are as follows: The soils in the study area have a Se content of (0.05~0.76)×10^-6, which is higher than the background value of soils in Tibet (0.15 ×10^-6); 76.83% of the land in the study area has sufficient Se, and land in the study area with a Se content of greater than 0.3 ×10^-6 covers an area of 45.43 km², as determined according to the standard threshold of Se content in alkaline soils (w(Se)≥0.3 ×10^-6). Further investigation shows that highland barley seeds have a Se content of (0.017~0.17)×10^-6 (average: 0.063 ×10^-6) and rapeseeds have a Se content of (0.043~0.14)×10^-6 (average: 0.078 ×10^-6) in the distribution area of Se-rich soils. As indicated by the root soil results of the zones with Se-rich soils, the Nieru Group controls the source of Se in soils, and Se and effective Se content in the soils are significantly positively correlated with N, P, alkali-hydrolyzable nitrogen, and rapid available phosphorus but is significantly negatively correlated with pH. These results indicate that the behavior of Se is significantly affected by a large number of nutrient elements in the soils and pH. Overall, the distribution areas of Se-rich soils in Bailang County have high soil environmental quality, crops with a high Se content, and great potential for the development of Se-rich plateau characteristic agricultural products.