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Active source surface-wave exploration has become one of the common methods for obtaining shallow urban subsurface structures. The method offers the advantages of being non-destructive, easy to operate, and providing reliable results. Obtaining accurate dispersion curves is a key factor for the successful application of this method. Currently, most researchers believe that surface wave energy constitutes a large proportion of the seismic records, while the energy of other seismic waves (such as body waves) is relatively small. Therefore, there is no need to remove clutter waves other than surface waves when calculating surface wave dispersion. However, this paper compares the effects of dispersion imaging obtained with and without clutter wave removal through numerical simulations and field tests. The results indicate that when the measurement alignment is short (generally less than 20 m), clutter waves can cause varying degrees of "distortion" in the dispersion curves, deviating from the real dispersion curves. Conversely, after removing clutter waves, the "distortion" can be corrected, leading to more accurate dispersion imaging. Therefore, we recommend conducting clutter removal processing when the measurement alignment is short. This paper proposes a stable and feasible clutter wave removal method that can effectively suppress clutter interference and improve the accuracy of dispersion imaging. The research in this paper provides an alternative and optimized solution for the pre-processing of near-surface active source surface-wave exploration. • When survey line length is shortened, dispersion curves of active-source seismic records deviate from true values. • We analyzed reasons for dispersion curve distortion from short survey lines and proposed a clutter wave removal method. • The effectiveness of the clutter wave removal method has been verified through numerical simulations and field experiments. [ABSTRACT FROM AUTHOR]

The ultra-long coal mining face has the advantages of high recovery efficiency and low production cost; however, the widening of the coal face poses the difficulty of detecting the hidden geological bodies inside the coal face, and using conventional geophysical methods gives rise to imprecise detection results. Therefore, this paper proposes a transient electromagnetic perspective technology based on the conventional mining transient electromagnetic method. A long rectangular loop is used as the transmitting source in one coal mining tunnel of the coal mining face, and it is received in the opposite coal mining tunnel. This method is characterized by a long detection distance and high construction efficiency. Firstly, the paper used numerical simulation to investigate the spread of the transient electromagnetic field from the long rectangular loop source in both a uniform full-space model and a full-space laminated model. This showed the transient electromagnetic field propagation law and the effect of the coal seam thickness. Then, we analyzed the transient electromagnetic perspective signal characteristics of typical geological structures and gave the all-time apparent resistivity calculation method. Conclusively, the feasibility of this method is ultimately confirmed by the analysis of the measured data. Also, the research results provide a new technological approach to detecting hidden geological structures in the ultra-long coal mining faces. • Propose transient electromagnetic perspective technology. • The transient electromagnetic field diffusion characteristics of the long rectangular loop is analyzed. • Geological structure in the ultra-long coal mining face is effectively detected. [ABSTRACT FROM AUTHOR]

Median filters are often used in simultaneous source data to remove sudden noise disturbances. Nonetheless, the median filter has a poor ability to process random noise, which can affect its performance in seismic data processing. This paper introduces a novel filtering method, a structure-oriented space-varying alpha-trimmed mean filter, which is an improvement of median filtering, and can deal with random noise better. The proposed filter's window length can be adaptively adjusted based on geological conditions, enabling the effective removal of spiky noise during simultaneous source acquisition and common random noise in geological exploration. This paper introduces the main differences between different types of median filtering methods and provides an overview of the principles and steps involved in our proposed approach. Our method's effectiveness is evaluated through its application to both simple synthetic examples and field data, alongside a comparative analysis against other existing approaches. The results of this research demonstrate that the approach we proposed here can efficiently make spike-like noise and random noise disappear while simultaneously maintaining vital signal characteristics. • The experiment separates simultaneous sources and suppress random noise. • The deblending effect of different methods based on filtering method is compared. • Deblending in the flatted dimension preserves most of the useful signal. [ABSTRACT FROM AUTHOR]

This paper reports the use of inclined sandstone specimen in the uniaxial compression tests to achieve the combined compression and shear loading (CCSL) state. A series of CCSL tests are performed on the inclined specimens with an inclination angle of 0°, 3°, 5°, and 7°. Acoustic emission (AE) and electromagnetic radiation (EMR) during the failure process are monitored. The results show that the additional shear stress component caused by the inclined shape configuration of tested specimens has significant effects on the failure mode and mechanical properties. The increase of inclination causes the failure mode to transit from the axial splitting to shear failure, and decreases the peak strength and elastic modulus of the inclined specimens. The specimen inclination lowers the damage prior to the peak stress, but stimulates the damage development after the peak stress. EMR has better correlation with stress drop than AE. The 65% of the peak strength is defined as the stress threshold of rock failure. The inclination angle lowers stress threshold of rock failure and accelerates failure initiation • Inclined rock specimens are uniaxially compressed to fulfill the combined compression and shear loading. • Inclination angle effect on the mechanical properties of inclined rock specimens is studied. • AE and EMR responses during failure process are analyzed. • Damage evolution of the inclined rock specimen is described based on AE and EMR parameters. • Correlations between AE and EMR and stress drop are quantitatively evaluated [ABSTRACT FROM AUTHOR]

This paper focuses on the natural radioactivity concentrations of 238U, 232Th, and 40K in the eruptive products of the Gölcük Volcano (SW Turkey) and its environmental radiation risks. Concentrations of these radionuclides (238U, 232Th, and 40K) have been measured on different igneous rocks, using a portable gamma-ray spectrometer at 450 points. Based on the obtained data, distribution maps of these radionuclides and the maps showing the absorbed dose rate in the air and radiogenic heat production (RHP) have been generated. We conclude that tephriphonolite and trachytes in potassic-ultrapotassic character display high radioactivity levels. On the other hand, it is revealed that the absorbed dose rate in the air ranging from 21 nGy/h to 482 nGy/h has been calculated as 8 times more than the world average (55 nGy/h). The results indicate that this region has crucial importance on human health and the environment. Therefore, the area requires special attention in terms of radiological hazards and further research should be done in the area regarding this issue. • Radionuclide concentrations definition using the gamma-ray spectrometer in Gölcük volcano. • The comparison of radionuclide concentrations with geology. • The absorbed dose rate in the air has been calculated as 8 times more than the world average. • Radiological hazards on human health and the environment have been determined. [ABSTRACT FROM AUTHOR]

In the presence of anisotropic resistivity structures, Magnetotelluric (MT) data inversion based on an isotropic resistivity model will be insufficient. Recent work on anisotropic MT inversions is primarily conducted using gradient-based, deterministic methods which may converge towards local minima and in general, suffer from ill-posedness of the inversion problem. Alternatively, meta-heuristical methods, such as Particle Swarm Optimization (PSO), are able to find the global minima of cost function. At the same time, they are easy to implement and do not require access to the dense Jacobian (and Hessian) matrix as needed by deterministic inversion methods. In this paper we propose PSO inversion for the anisotropic MT inversion problem using an adaptive inertia weights control strategy to balance exploration and exploitation during the PSO search. Higher order differential regularization is introduced with a Gaussian filter, where the conventional first order, Occam-like regularization term is replaced by a variance term. We investigate the performance of the proposed PSO inversion for an isotropic as well as an axial anisotropic synthetic case to demonstrate improvements over an Occam-like regularization. For the COPROD2 benchmark data set, the proposed PSO inversion can not only reproduce the extend of the North American Central Plains (NACP) conductive anomaly, but also to predict an anisotropy ratio of two orders of magnitude, which is in accordance with laboratory findings. • Magnetotelluric 2D anisotropic inversion with particle swarm optimization. • Adaptive inertia weight balances exploration and exploitation of PSO. • Model smoothing achieved via Gaussian filtering. • Anisotropic structure has been predicted for the NACP anomaly of COPROD2 data. [ABSTRACT FROM AUTHOR]

Hessdalen valley in Norway is known for luminous phenomena suddenly and evenly appearing temporarily. Since several decades, these phenomena are observed by many witnesses, and they are sometimes traced by geophysical devices. The first appearance in modern times was reported in 1981 but systematic observations started during winter of 1984 when the Hessdalen project was launched. Later, Østfold University College led the project and yearly organized one to two field campaigns, with the objective to systematically record and investigate the phenomenon. Till that epoch, detailed tectonics, fault systems and superficial conductive structures remained unknown. Therefore, during the last years, VLF surveys have been performed in Hessdalen valley as part of six geophysical field campaigns which sometimes also included Total Magnetic Field and Self Potential spatial ground measurements. VLF measurements have been carried out on a 20 m average spacing along many traces totaling to100 km length. The entire covered area was about 100 km2.In this paper, we focus on the results of the VLF measurements. Several conductive zones have been found. They are mainly related to mineral deposits (mainly sulfides). The trace at the ground surface of these conductive zones could suggest that they draw an ellipse of 6 by12 km, related to the shape of the gabbro intrusion present in the area and oriented in the SW-NE direction. The results combined with other geophysical data contribute to better understand how the near surface structures (depth less than a few hundred meters) could supply the generation of the so-called Hessdalen lights ('HL') and explain why these lights appear inside this valley. The particular geological structure detected in Hessdalen valley may encourage similar campaigns in other areas where similar phenomena are observed. • Transient appearance of luminous phenomena in the sky of Hessdalen valley • Inter-relationship between geomorphology, mineral deposits, electromagnetic field and low atmospheric physics and luminous phenomena • Local geological structure may favorize Luminous phenomena genesis. [ABSTRACT FROM AUTHOR]

The paper presents an electromagnetic geothermometer-based two-dimensional temperature model for the Travale (Italy) enhanced geothermal system derived from magnetotelluric and temperature data. Joint analysis of the temperature and electrical resistivity models made feasible a new self-consistent conceptual model of this site, which agrees with available geological data and previous geophysical results. It explains the nature of seismic reflection horizons detected in 1978 and unusual seismicity distribution in depth which could not be properly addressed earlier without temperature predicting beyond boreholes. It is concluded that the heat source feeding this system may be a granitic intrusion located at a depth below 4 km, which corresponds to the isotherm of 600 °C. A sharp temperature gradient above this intrusion forms a contact thermo-metamorphic halo in the depth range of 3–4 km. Assessment of the released fluid volume fraction from the electrical resistivity model indicates that the general amount of thermo-metamorphic and magmatic fluids in the rock-dominated Travale geothermal system is negligible. It is concluded that meteoric waters are the main source of fluids penetrating along normal faults up to 3 km. Despite some supercritical fluids of thermo-metamorphic origin could circulate in the system below this depth, their amount is hardly sufficient for economically justified exploration drilling. The results of the study indicate that building the temperature model of the geothermal area is crucially important for the exploration of enhanced geothermal systems. • Temperature model of the Travale geothermal area is built using EM geothermometer. • New conceptual model of the Travale geothermal system is suggested. • Nature of two seismic reflecting horizons detected 45 years ago is explained. • Maximal number of earthquake hypocenters in the depth range 3–4 km is explained • Amount of supercritical fluids below 3 km does not justify exploration drilling. [ABSTRACT FROM AUTHOR]

In this paper, we first derive the dynamic solution in a transversely isotropic (TI) elastic and layered half-space, induced by a time-harmonic vertical load on its surface. The solution is obtained via the efficient and unconditionally stable dual variable and position (DVP) matrix method along with the fast Fourier-Bessel series (FBS) expansion approach. In order to study the effect of material anisotropy, the degree of anisotropy, namely the ratio of the horizontal Young's modulus over vertical Young's modulus, is introduced as the key parameter, with a very reasonable assumption on other involved elastic constants in the layered TI half-space. This enables us to investigate the effect of material anisotropy on the wave Green's functions, dispersion curves, ellipticity, and polarity. By comparing with the effect of Poisson's ratio in the corresponding layered isotropic (ISO) half-space, we observe that nearly all the wave features with varying degrees of anisotropy in the TI layered half-space are similar to those with varying Poisson's ratio in the corresponding ISO half-space. This indicates the challenge or non-uniqueness in the inversion of TI velocity profiles using vertical surface loading only. • Unconditionally stable DVP matrix method is combined with the fast Fourier-Bessel series expansion. • Wave characteristics are comprehensively examined in terms of Green's function, waveforms, ellipticity, and polarity. • A more reasonable assumption of independent TI elastic constants is proposed to better represent the degree of anisotropy. • Degree of anisotropy is found to have similar effect on all aspects of wave characteristics as Poisson's ratio. [ABSTRACT FROM AUTHOR]

Reconstructing in different partitions independently is one of the effective strategies to implement 3D seismic data reconstruction. However, if this strategy is used, the underlying correlations between two adjacent partitions will be neglected. To solve this problem, this paper introduces curvelet transform and provides an improved projection onto convex sets (POCS) method with weighting operator, based on the continuity between two adjacent time slices, to reconstruct each time slice. For each time slice, we constructed this weighting operator based on the support estimation given by the adjacent reconstructed time slice in curvelet domain. Thereby, we provided a 3D seismic data reconstruction method using prior support information. The experiments for both synthetic data and field data demonstrated that our method is superior to the traditional POCS. • Three-dimensional seismic data reconstruction using prior support information. • Better effect and higher convergence speed than traditional method. • Easy to expand to higher-dimensional reconstrution. • Easy to combine with different sparse transformations. [ABSTRACT FROM AUTHOR]

As a result of the combined influence of multi-stage and multi-directional tectonic activities, the subsurface medium in complex structural areas can easily develop intricate fault systems with varying scales and directions. Post-stack seismic and azimuth-stack attributes have limited precision in recognizing such complex fault systems. In this paper, we propose an adaptive fault enhancement workflow in offset vector tile (OVT) domain based on anisotropy theory to improve the recognition ability of seismic data for multi-directional faults and minor faults. The vertical directions of fault strikes and tectonic strikes estimated by the gradient structure tensor (GST) can be used as sensitive observation azimuths of faults. At the same time, according to the anisotropic forward modeling and real data amplitude variation with offset (AVO) analysis of minor faults in marine shale of Wufeng-Longmaxi formations in Sichuan Basin, China, the incident angles with the largest difference between isotropic and anisotropic reflection coefficients can be used as sensitive incident angles of faults. A new fault enhancement seismic data can be reconstructed from the OVT gathers by traversing the sensitive azimuths and incident angles adaptively. The 3D model and real data indicate that the faults enhanced by the workflow we proposed are clearer in shape, smaller in scale, and richer in details, which is consistent with geology and well. • We propose an adaptive fault enhancement workflow in OVT domain. • The workflow considers the azimuth and incidence contained in OVT gathers. • We discussed the recognition ability of angle stack for minor faults. • The result of shale reservoir in Sichuan Basin is consistent with geology and well. [ABSTRACT FROM AUTHOR]

Reliable density information is an essential factor in lithologic interpretation and reservoir evaluation. However, density reconstruction is hampered by a lack of long-wavelength information and the crosstalk between different parameters. The powerful nonlinearity in density inversion constrains the multi-parameter full waveform inversion application. This paper introduces the Wasserstein distance into the full waveform inversion for velocity and density based on the optimal transport theory. We construct an objective function with better convexity to avoid the cycle-skipping caused by the poor initial model. Furthermore, due to the sensitivity of the quadratic Wasserstein distance to low-frequency, we add the low-wavenumber component absent in the conventional density inversion. We acquire a long-wavelength density background using optimal transport inversion and then apply it as an initial model for least-squares inversion. Numerical examples show that our optimal transport inversion effectively builds a reasonable density background model for FWI. Density inversion can be improved by incorporating optimal transport and least-squares theory, leading to a reliable quantitative description for petroleum exploration and development. • Introducing the Wasserstein distance into full waveform inversion to build a low wave-number density structure. • Developing a stepwise density inversion approach utilizing the least squares norm and Wasserstein distance. • Mitigating the impact of inaccurate initial models on density inversion. • Improving stability and accuracy of density reconstruction compared to conventional inversion. [ABSTRACT FROM AUTHOR]

Accurate fault identification provides an important basis for well location deployment, oil and gas resource development. However, obtaining a large number of fault samples through manual labeling or interpretation is difficult. Conventional convolutional neural networks have certain challenges in finely characterizing low-order faults and fault continuity. This paper studies a 3D intelligent fault identification method that integrates deep learning with attention mechanism. Based on 3D-UNet network, the method constructs a dual attention fault identification model with an encoder-decoder structure, which focuses on enhancing low-order fault information and extracting key features. An adaptive hybrid loss function is proposed to address the imbalance problem of fault proportions in seismic amplitude data. The function introduces an adjustment coefficient to adaptively enhance the attention to high-order or low-order faults according to the actual situation of the fault, improving the accuracy and continuity of fault identification. Furthermore, a model re-training learning optimization method is presented to capture the missed fault information in the first training and repair the connectivity of low-order faults. Applying this method to the synthetic data set, the accuracy can be improved to 0.9732, and the loss can be converged to 0.0982. The results of shale reservoirs in the North Sea Basin and Kerry-3D indicate that the method can reduce the situation of fault missing and misidentification, effectively improve fault identification accuracy, and enhance low-order fault identification by obtaining more contextual fault features. • A seismic fault image segmentation network is developed with attention mechanism. • Construct an adaptive hybrid loss function to solve the problem of data imbalance. • A method retraining learning that integrates theory and predictive data is proposed. [ABSTRACT FROM AUTHOR]

The grid tomography velocity inversion method prevails as the most efficacious technique for acquiring background velocity requisite for migration. Originating from imaging gathers, this method not only inverses velocity but also subsequently ascertains the anisotropic parameters field. Traditional approaches utilize a parameter field discretized in a rectangular grid for both ray tracing and parameter inversion. However, the rectangular grids may not provide optimal accuracy for structures with pronounced lateral parameter variations. In contrast, triangular grid discretization allows for grid division along steep slopes, offering sparsity and flexibility when juxtaposed with conventional rectangular grid methods. This paper introduces an optimized triangular grid travel time parameter tomography inversion method, formulated on the parameter sensitivity to travel time and employing angle gathers to derive travel time residuals. Analytical modeling and real data processing substantiate that the triangular grid ray tracing method ameliorates the ill-conditioned nature of the tomography equation and enhances the accuracy of the inversion parameter field effectively. • Ray tracing for obtaining sensitive kernel functions in triangular meshes • Improving the continuity of mid deep and steep structural layers • Layer constraints can improve inversion accuracy. • Accurately simulate undulating layers and velocity interfaces on triangular grids. [ABSTRACT FROM AUTHOR]

Convolutional Neural Networks (CNN) are widely applied to Ground Penetrating Radar (GPR) inversion because they have strong data-driven capabilities and are suitable for the data structure form of GPR. For CNN, the computation increases with the distance that the convolutional block moves from one region to another when it calculates the relationship between two regions. For GPR data, the target reflection exists in the surrounding traces and full time-window of the target, which leads to high degree of remote relationship. In this paper, we propose GPR-TransUNet, a deep-learning based inversion network which use self-attention mechanism. According to the characteristics of GPR data, regression network and GPR-Loss mechanism were used. Both numerical and model experiments were arranged to test the performance of the network, and the result as well as comparative analysis demonstrate the superiority of GPR-TransUNet. Finally, we applied this method to the field GPR data of Guangxi as an attempt. [Display omitted] • GPR-TransUNet based on Regressive Self-Attention Mechanism and U-net is proposed. • GPR-TransUNet is successfully used to reconstruct the permittivity map of complex subsurface defects. • GPR-TransUNet is verified by synthetic and field data. [ABSTRACT FROM AUTHOR]

Microseismic technology has been widely used in geological hazard monitoring. However, the effective identification and classification of microseismic events in mines have always been a challenge in hazard monitoring. In this paper, a new method combining the empirical mode decomposition (EMD) algorithm and artificial neural network is proposed for the classification and identification of microseismic waveforms. This is the first study to explore such a model in the microseismic monitoring of coal mines. The data for this study were collected from a coal mine in northern China. A total of 2768 microseismic events and 2435 non-microseismic events were manually selected from a large amount of data. Firstly, the microseismic waveform reconstruction was performed using the 4th to 8th Intrinsic Mode Function (IMF) obtained by the EMD algorithm. Secondly, the peak factor, clearance factor, impulse factor, kurtosis, skewness, and waveform factor of each reconstructed microseismic waveform were used as features. Subsequently, the convolutional neural network (CNN) was used to classify microseismic events. Among them, data from 3600 microseismic events were used as the training set, and data from 1603 microseismic events were used as the test set. Finally, the original waveform data were used as input and compared with the classification results processed with the EMD algorithm. The classification methods of the BP neural network and Radial Basis Function (RBF) neural network were used for verification. The results of the processed features showed a significant increase in accuracy. The classification accuracy of CNN, BP neural network, and RBF neural network are 97.37%, 91.99%, and 94.23%, respectively. The results show that the utilization of the feature processing technique and CNN algorithm in this study demonstrates superior efficacy in microseismic event classification, which can be used in practice. • The EMD algorithm and ANN was constructed to classify microseismic waveforms. • Six features of the reconstructed waveform were selected as the classification basis. • The EMD algorithm was used to make the six waveform characteristics more significant. [ABSTRACT FROM AUTHOR]

This paper studies the propagation of oblique incident seismic P waves as they pass through joints containing saturated fluids with different media on both sides. For joints containing saturated fluids, the viscoelastic model is used to study the dynamic deformation characteristics. The complete solution for seismic P waves propagating through joints is derived. The reflection and transmission coefficients that occur at arbitrary angles for different ratios of wave impedance are studied. The effects of the frequency, viscosity coefficient and ratio of wave impedance on the reflection and transmission coefficients are discussed. The results show that the reflection and transmission coefficients vary continuously as the angle increases when the ratio of wave impedance is <1.00. However, when the ratio of wave impedance is >1.00, the reflection coefficients are continuous, but the transmission coefficients are discontinuous. When the viscosity of the joint is not considered, as the frequency of the incident wave increases, the reflection coefficients of the reflected P wave and SV wave increase, the transmission coefficient of the transmitted P wave decreases, and the transmission coefficient of the transmitted SV wave first increases and then decreases. When the viscosity of the joint is considered, the difference between the reflection and transmission coefficients under different viscosity coefficients decreases as the frequency increases. Moreover, with increasing values of the viscosity coefficient, the reflection and transmission coefficients are closer to those values that viscosity is not considered. The results also show that the reflection coefficients are continuous, while the transmission coefficients are discontinuous as the ratio of wave impedance increases. • P wave through joint containing saturated fluid with different media was studied. • The analytical solutions of reflection and transmission waves were derived. • Effect of viscosity coefficient on reflection and transmission was discussed. • Effect of ratio of wave impedance on reflection and transmission was studied. [ABSTRACT FROM AUTHOR]

This paper describes some numerical experiments for stress modeling in the zone around a reservoir in a sedimentary basin, where oil and gas exploration is real or potential. We aim to map mainly low- and high-pressure zones, under the principle that they act as push-and-pull natural pumps for fluid accumulation. The necessary data for practical work is based on seismic data, as a post-migration process with the knowledge of velocities of the P and S waves, and the density information. The computation is designed for simple geometries to represent a reservoir geology, and it is addressed as a boundary value problem (BVP) involving the Beltrami-Michell's partial differential equation with Dirichlet conditions. The method employed was the Green's function expressed by Fourier series for the solution of the BVP, where the boundary conditions are given by the stress components along the boundary of the target volume. The first stress invariant controls the elastic mechanical behavior of the subsoil; therefore, once the distribution of rock pressure is obtained, and the boundary conditions are defined, solving the BVP allows the calculation of the stress components distribution (normal and tangential) within a separate target volume for details. The relationship between rock pressure and stress components is established by the Beltrami-Michell problem, which takes the form of a Poisson's equation. The proposed method was applied in a more complex target zone present in the Marmousi model, which contains reservoirs within regions of interest, expanding to more realistic complex problems. [Display omitted] • The low- and high-pressure zones act as natural pumps for fluid accumulation. • The first stress tensor invariant rules the subsoil elastic mechanical behavior. • The Beltrami-Michell equation relates rock pressure and stress tensor components. • The Beltrami-Michell solution is closely related to stress boundary conditions. • The Poisson's ratio values can cause deviations in the expected solution. [ABSTRACT FROM AUTHOR]

Pre-stack seismic amplitude versus offset (AVO) inversion estimates reservoir properties by relying on the variation of seismic data amplitude with offset, usually ignoring the role of frequency information in seismic data, which leads to its limited and incomplete use of seismic data. Because the reservoir medium has certain viscoelastic properties, its seismic response changes with the offset, and also has a frequency variation response. The traditional linearized PP wave reflection coefficient of viscoelastic medium is only suitable for small angle incidence, and the inversion based on this equation is difficult to meet the requirements of high-precision parameter estimation for complex media. In this paper, starting from the scattering matrix of a viscoelastic medium, a modified second-order viscoelastic scattering coefficient equation based on perturbation theory is derived, and a nonlinear inversion strategy based on the combination of amplitude and frequency is proposed. The new equation has a wider application range because it considers the viscoelasticity and nonlinear approximation of the medium at the same time, and includes five model parameters to be inverted, namely the P-wave velocity, S-wave velocity, density, quality factor (Q-factor) of P-wave, and Q-factor of S-wave. Accuracy analysis shows that the newly proposed approximation equation is more accurate than the traditional linear approximation equation. In addition, a pre-stack seismic nonlinear frequency-dependent inversion method for viscoelastic media is proposed, which realizes the simultaneous estimation of five model parameters. Synthetic example and field seismic data set are also used to demonstrate the stability and accuracy of the proposed method. • A second-order viscoelastic scattering coefficient equation of P -wave reflectivity is derived based on perturbation theory. • A high-order pre-stack seismic nonlinear frequency-dependent inversion method (FANNI) is proposed. • Through the proposed FANNI inversion method, the high-precision direct extraction of quality factors can be realized. [ABSTRACT FROM AUTHOR]

The anisotropic ray tracing equations of elastic waves are derived for calculating the central ray's travel time, trajectory, and parameters P and Q. Based on the anisotropic ray tracing algorithm, we proposed a transversely isotropic elastic dynamically focused beam migration for two dimensional media. Based on the two dimensional Kirchhoff-Helmholtz integral of elastic waves, the elastic imaging weight coefficients are used to reduce the crosstalk noise. Then, based on the previous research, we introduced a sign function to eliminate the effect of polarity reversal in qPqSV wave migration. Through model tests, it can be found that the proposed method can process the multicomponent seismic data and image the complex structures for anisotropic media. The optimized dynamic ray tracing algorithm is superior to the conventional one in computational efficiency. Furthermore, the proposed method eliminates the limitations of the Gaussian beam imaging. This method not only does not affect the accuracy of shallow imaging, but also enhances the energy focusing and the amplitude of deep layers. The model tests have shown the accuracy and effectiveness of our proposed method. • Based on the previous research, an anisotropic ray tracing equation of elastic waves is derived. • A dynamically focused beam migration of elastic waves in TI media is developed in this paper. • A sign function is introduced to solve the polarity reversal problem in converted wave migration. [ABSTRACT FROM AUTHOR]

Attenuation of incoherent noise can effectively improve signal-to-noise ratio (SNR) of seismic data. Recently, unsupervised denoising methods have emerged as solutions for the data collection problem to learn directly from single noisy data. However, the loss of input information based on their blind spot strategy leads to poor denoising performance. In this paper, we propose a complementary mask unsupervised learning framework based on visible blind spot (CMVB) to overcome the information loss. First, a Splitter-Splicer is designed to act on the complementary mask of the input. This approach makes full use of all the data to preserve weak signals. Second, a new blind-spot-based loss function is proposed to integrate blind-spot and non-blind-spot data. The addition of non-blind-spot data enhances the continuity of seismic events. Finally, the attention mechanism is integrated into the encoder-decoder structure, improving the ability of blind spot networks to capture detailed information. Experiments are conducted on three synthetic datasets and two field datasets to compare with two existing state-of-the-art unsupervised denoising methods. The results demonstrate that our method excels in recovering weak reflections. • A new unsupervised learning framework. • Complementary blind-spot sampling alleviates the data loss problem. • Designing visible blind loss functions for application to seismic data denoising. • Excellent denoising performance on background noise and natural unknown noise. [ABSTRACT FROM AUTHOR]

Seepage is a common phenomenon in earthfill dams, and one that typically warrants episodic assessment and monitoring by regulatory agencies. Geophysical surveys provide a convenient, cost-effective, and convenient means for assessing seepage, but only if they are applied in effective combinations and if the data are analyzed properly. In the present study, a self-potential survey of streaming potential and a 2D electrical resistivity tomography survey were notably successful in detecting seepage under the embankment of the nearly 90-year-old Standing Rock Dam No. 1 in South Dakota, USA. Self-potential (SP) measurements show a localized negative anomaly of up to 27 mV on the upstream side of the dam, which we interpret to be the inlet or recharge zone for seepage, and a positive anomaly of up to 20 mV on the downstream side, which we interpret to be the outlet or discharge zone. The spatial correlation between our resistivity models, SP data, and topography was excellent. Water-saturated, conductive deposits in the dam's embankment match a negative SP amplitude in the inlet or recharge area. Similarly, water-saturated electrically conductive sediments are characterized by a positive SP amplitude in the discharge area where surface seepage occurs in a topographic low. Six years of water-level measurements in the existing piezometers interpreted relative to the properties and spatial distribution of coarser-grained alluvium (sand and gravel) underneath the dam's embankment fill, suggest that most seepage occurs under the dam. Our approach to assessing seepage in this project should be widely applicable to earthfill dams worldwide, and our modeled results constitute a valuable case study. • This paper is an integrated geophysical and geotechnical investigation of water seepage through earthfill dam. • We used 2D resistivity and Self-Potential methods to discover the seepage zone. • The geotechnical data explained the main reason for seepage under the dam. • The streaming potential created by water flow is a key to detecting the seepage zone. [ABSTRACT FROM AUTHOR]

Accurately determining the parameters of the dynamic constitutive model is significant to analyzing the dynamic response characteristics of the surrounding rock at the proximal and distal ends of a railroad tunnel blasting. Hence, this paper analyzes the propagation and attenuation of blasting vibration waves in the rock by utilizing the vibration velocity monitoring data of the Xinbin Tunnel at the Liaoning section of the Shenbai High-speed Railway. The data are provided by the drilling and blasting method. Additionally, the IA-BP inverse analysis method was established to invert the parameters of the JH-2 constitutive model of the rock by numerically analyzing the simulated blasting vibration waves using the inversion parameters. The results highlight that the inversion value obtained by the IA-BP algorithm is slightly different from the calculated test value but still highly accurate, demonstrating the rationality of the inverse analysis method. Meanwhile, the numerical simulation results supplement the proximal vibration velocity, which is difficult to monitor in the project. This is because the vibration velocity of the tunnel surrounding the rock has a noticeable directional effect. Specifically, the vibration velocity law varies as the blast center distance increases, where the peak vibration velocity direction at the far end of the blast changes from the Y direction (vertical direction) to the Z direction (blast direction). The linear attenuation formula of the vibration velocity in the three principles of the tunnel arch, arch shoulder, and arch foot is obtained by fitting, which is an adequate prediction of the safety of the subsequent construction. • A large number of on-site monitoring for the blast distal vibration velocity. • The formula for the attenuation of blasting distal vibration velocity in different locations and directions is derived. • The difficult problem of determining the parameters of the surrounding rock at the site is solved. • The differentiated analysis of blasting proximal vibration velocity and blasting distal vibration velocity are realised. [ABSTRACT FROM AUTHOR]

Downward continuation is a useful transformation in the processing and interpretation of potential field data. However, this transformation is known for its inherent instability. In this paper, we proposed a stable iterative Runge-Kutta method for downward continuation that uses an average slope over the interval of continuation. Because of the truncation error, we combine the ideas of Runge-Kutta with the iterative downward continuation methods in a single method to improve the accuracy and the precision of the method. The presented method needs only the computation of the first order vertical derivatives (slope) over the whole interval of continuation using the Tikhonov regularization. To validate the efficiency of the proposed method, various tests were conducted on synthetic magnetic data as well as real aeromagnetic data. The obtained results clearly show the stability of our method for the downward continuation of potential field data. • We present a new method for downward continuation based on an iterative process using the Runge-Kutta method. • Our method is stabilized using the Tikhonov regularization process, and the optimal value of the regularization parameter is selected based on the c-norm criterion. • Our study shows that the developed method has a high correlation rate close to 98% when applied to synthetic data and can be used for a variety of potential field data. • The results suggest that our method efficiently reduces noise. • Our method is a valuable tool for geophysicists working with potential field data. [ABSTRACT FROM AUTHOR]

Waveform stacking is frequently employed in the analysis of microseismic data due to its adaptability, effectiveness, and noise immunity. However, the low signal-to-noise ratio and inaccurate velocity model have a considerable negative impact on the waveform stacking location method's performance. A time-frequency transform-based characteristic function and the addition of a multi-master event method to waveform stacking location are presented as solutions to the aforementioned issues. In this paper, non-smooth statistical features of characteristic function are extracted and enhanced using time-frequency transform. Based on the two-pair double-difference method, multi-master events are introduced and a reference criterion for selecting the master events is proposed. Experiments with simulated and actual microseismic data show that the conversion of time-domain signals into time-frequency signals by wavelet transform can enhance the peak capacity of the signal and reduce the background noise, enhancing the imaging resolution. The introduction of multi-master events not only reduces the sensitivity of the waveform stacking method to velocity error but also improves the clustering effect of the master event method. • Using multi-master event waveform stacking to localize microseismic. • Time-frequency transform-based characteristic functions are proposed • The multi-master event waveform stacking method is more stable and accurate, and less sensitive to velocity models [ABSTRACT FROM AUTHOR]

Heat supply pipelines are a critical component of urban infrastructure, with numerous underground projects relying on this crucial and often concealed system. In cases where blueprints are unavailable, it is crucial to determine the precise location and depth of heat supply pipelines. One of the most straightforward methods for detecting these pipelines is measuring underground temperature. Temperature gradient data is less sensitive to environmental temperature changes for detecting shallow heat sources than temperature data. This paper presents an extension of the correlation imaging method to handle temperature gradient data. This method can accurately determine the horizontal center position and the depth of the heat source. This temperature tomographic approach is reliable and has a high resolution, as evidenced by both synthetic and field examples. • Extended the correlation imaging method to process temperature gradient data. • Determined the optimal duration for measuring geothermal gradient data through field experiments. • Located the heat supply pipeline using temperature gradient data measured from the shallow underground. [ABSTRACT FROM AUTHOR]

The Laojunshan ore cluster region is situated at the north Song Chay dome, which is the junction of the Yangtze, the Cathaysia, and the Indo-China Blocks. The north Song Chay dome characterized by the Laojunshan metamorphic core complex is an important ore-forming region for W-Sn-Pb-Zn-In elements related to the Late Cretaceous granitic magmatism. In this paper, the Bi-dimensional empirical mode decomposition (BEMD) is applied to separate gravity components from the original gravity data, combined with the known geological and mineralized information, to explore the relationships between the gravity components and various ore-controlling factors at different depths. Four intrinsic mode functions (IMFs) and a residue are obtained. They may imply the spatial distribution of the geological bodies with featured gravity components at different depths. The results are shown as follows: (1) The low-pass filtering gravity component (BIMF4) implies the deeply buried geological units in the study region. The Cretaceous Laojunshan granitic complex and the Nanwenhe gneissic granite display negative gravity components and weak positive gravity components, respectively. The former is closely related to Sn-Zn-In mineralization, the latter is closely related to W polymetallic deposits. Therefore, the negative gravity components showing the Laojunshan granitic complex are the prospecting targets for deeply buried Sn-Zn-In deposits. The weak positive gravity components displaying the Nanwenhe gneissic granite are the prospecting targets for deeply buried W polymetallic deposits. (2) The band-pass filtering gravity component (BIMF3) implies the geological units at middle depth. The skarn-type Sn-W polymetallic deposits are observed in the transition zones from the positive to the negative gravity components, which coincide with the contact metasomatic zones between the Cretaceous granite and the Cambrian-Devonian carbonate rocks. Some small quartz vein W deposits occur within the Cretaceous Laojunshan granite with negative gravity components, and some layered W deposits occur in the Silurian gneissic granite with a weak positive gravity component. (3) High-pass filtering gravity component (BIMF2) implies geological units at the shallow crust, which shows that most of the deposits (occurrences) are located within the positive gravity component zones. These positive gravity component zones should be ore-finding targets for further prospecting for the undiscovered Sn and W polymetallic deposits. (4) The gravity components separated by BEMD coincide with the spatial distribution of the granites associated with various types of mineralization and alteration zones at different depths, which will give insights for further prospecting for concealed ore bodies in this study region. [Display omitted] • The mineralized characteristics of both the Sn-Zn-In and the W polymetallic deposits are recognized. • The gravity components implying ore-controlling factors at different depths are separated using BEMD. • The ore-finding targets of both the Sn-Zn-In and the W polymetallic deposits are identified using the gravity components. [ABSTRACT FROM AUTHOR]