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This paper presents the integration of advanced 3D digitization and visualization technologies in the study and preservation of prehistoric megalithic heritage sites in the Mediterranean. We focus on the digital documentation and analysis of the Borġ in-Nadur megalithic complex and other notable sites, employing a combination of terrestrial laser scanning, aerial and terrestrial digital photogrammetry. The research highlights how digital tools not only enhance the precision of archaeological documentation but also promote virtual accessibility and offer new insights into the archeoastronomical significance of these structures. We discuss the production of high-resolution digital replicas, their utility in virtual reconstructions, and the role of digital platforms in public engagement and scholarly study. The findings underscore the potential of digital technologies to revolutionize heritage conservation and research, providing a comprehensive digital approach to the safeguarding and understanding of our ancient heritage. • The paper discusses how advanced 3D digitization and visualization technologies enhance the study and preservation of prehistoric megalithic heritage in the Mediterranean, focusing on the Borġ in-Nadur megalithic complex and other sites in Malta. • Terrestrial laser scanning, aerial, and terrestrial digital photogrammetry are employed to capture detailed representations of the structures, enabling high-resolution digital replicas for virtual reconstructions and analyses. • The production of digital replicas facilitates public engagement and scholarly study through virtual accessibility, allowing broader public interaction with heritage sites. • The research includes a new examination of the archeoastronomical significance of these structures, exploring how ancient builders may have aligned these sites with celestial events. • Digital technologies offer powerful tools for the documentation, study, and preservation of prehistoric heritage, providing strategies for safeguarding these sites against environmental and human threats. • The study outlines future research that will use digital preservation to further enhance the resolution and accuracy of 3D models, and integrate these models with virtual and augmented reality for educational and research purposes. [ABSTRACT FROM AUTHOR]

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 uniaxial compressive strength is one of the most important basic parameters of rock, which is essential for surrounding rock stability analysis and support scheme design of underground engineering. At present, it is time consuming and costly to take a large amount of core samples for laboratory testing, and the mechanical properties of the cores may be affected by mining disturbance, which can easily lead to inaccurate result. The measurement while drilling (MWD) technology provides a new approach to solve the above challenge. The key to implementing this technology is to establish a correlation model between drilling parameters and rock mechanics parameters. Based on the characteristics of polycrystalline diamond compact (PDC) bits in drilling and rock breakage, this paper analyzes the mechanical state of the bit in breaking rock. A theoretical correlation model between the torque, feed force of the bit and the uniaxial compressive strength of the rock has been developed. To verify the accuracy of the theoretical model, the uniaxial compressive strength of five different types of rocks (red sandstone, green sandstone, limestone, marble and shale) was obtained through laboratory mechanical tests. The torque M b , feed force F b and other parameters in the drilling process of these five rocks were tested through the newly developed MWD test system. The correlation between the drilling parameters and the uniaxial compressive strength of rock was established. The results showed that the feed force F b and torque M b measured at five different types of rocks indicate a linear increasing trend with an increase in depth of cut h. Meanwhile, a strong linear relationship between the feed force F b and torque M b is evident. This paper proposes an MWD-based method to rapidly conduct the in-situ measurement of the uniaxial compressive strength of various rocks. • The quantitative relationship between drilling parameters and rock mechanical parameters is obtained. • An experimental system for rock drilling and parameter testing is built. • A measurement while drilling method for in-situ measurement of the uniaxial compressive strength parameters of rock is proposed. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the full-waveform inversion (FWI) for recovering three media parameters of the poroelastic wave equations as training a neural network. We recast the poroelastic wave simulation in the time domain by the staggered-grid schemes into a process of recurrent neural networks (RNNs). Furthermore, the parameters of RNNs coincide with the inverted parameters in FWI. The algorithm of FWI with a stochastic gradient optimizer named Adam is proposed. The gradients of the objective function with respect to the media parameters are computed by the automatic differentiation. FWI is implemented numerically for three media parameters, i.e., solid density, Lamé parameter of of saturated matrix and shear modulus of dry porous matrix. The numerical computations with two designed models show the good imaging ability of the described method in this paper. It can be applied to invert more media parameters of the poroelastic wave equations. • We firstly investigate the poroelastic FWI with Adam by our knowledge. • Both variations and interface positions of parameters are inverted very well. • The inherent relationship between time-domain FWI and RNNs is expounded. • The automatic differentiation technique is applied to compute gradient. • The stochastic optimizer can help iterations escape from improper local minimum. [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 proposes a novel technique for reconstruction of a high resolution (HR) image by fussing irregularly sampled data of panchromatic image and multi-spectral image. The idea behind the fusion process is normalized convolution which uses the technique of approximating the local signals by projecting on to subspace. The normalized convolution used in this paper contains the polynomial basis functions similar to that of a Taylor series expansion. The window function used in the adaptive normalized convolution helps in improving the analysis by grouping more samples of same sense. This in turn helps to escalate the signal to noise ratio and curtail the diffusion across discontinuities. The necessity of multi-sensor data in required in many fields such as defense, remote-sensing, machine vision, medical imaging and the proposed method supplied promising results to such applications. • The algorithm for fusing the images is based on the supporting structure of Normalized convolution. • The idea is projection of local signals onto a subspace. • The adaptive nature of the window function helps to gather more samples and increases signal to noise ratio, decreases diffusion through discontinuities. [ABSTRACT FROM AUTHOR]

For soil exploration in the vadose zone, a high-frequency multi-channel analysis of surface waves (HF-MASW) method with three enhanced techniques has been developed. In this paper, we apply this enhanced HF-MASW method to re-process field testing data that were collected over the past several years on five different sites. These sites are selected for their different soil properties and data acquisition configurations. The derived overtone images, extracted dispersion curves, and inverted soil profiles of these soil sites are shown and discussed. Penetration tests were conducted and comparisons are made between the soil profiles taken from the HF-MASW tests and those from the penetration tests. One of the objectives of the paper is to determine the optimal data acquisition parameters, including the source parameters and sensor array geometric configuration through the discussions of these case studies. Practical concerns of the HF-MASW method and lessons learnt from these tests are addressed. Recommendations for data acquisition, signal processing, and inversion are provided. • Enhanced high-frequency multichannel analysis of surface wave (HF-MASW) method. • Reprocessing field data at five sites with different soil textures. • Soil profile measurements in the vadose zone. • Comparison of the soil profiles between HF-MASW tests and penetration tests. • Practical concerns and guidelines for conducting a HF-MASW test. [ABSTRACT FROM AUTHOR]

This paper seeks to explain the origin of sign reversal or zero-crossover effect observed at late decay times in the experimental data involving the application of SQUID in geophysical explorations based on TDEM technique. A complete SQUID based TDEM system has been developed and used for field survey after extensive characterization of the system in the laboratory. When the TDEM system was tested in a relatively noisy environment of the laboratory, the sign reversal effects was not observed but the effect was observed conspicuously in the experimental data recorded during an actual field survey at a site far away from the urban electromagnetic noise. The transient electromagnetic data recorded during the field survey showed that the decay transients surprisingly reached negative values in a terrain where a thin conducting layer is sandwiched between thick upper and thin lower resistive layers. The major advantage of using the SQUID sensor in TDEM applications is its ability to achieve extremely high sensitivity even at very low frequencies, enabling one to investigate the conductivity of the layers buried deep below the ground surface. While the decay transients recorded with the use of SQUID magnetometer were successful in providing information pertaining to the buried conducting layer, an unexpected zero crossover was found at later decay times as seen also by a few research groups in the past. The origin of this peculiar zero crossover has not been clearly established so far, and has been speculatively attributed to several parasitic phenomena such as instrumental drift, remnant responses of the previous transmitter pulses, induced polarization effect, poor offset removal, etc., Extensive analysis of our experimental data obtained in the field has, however, shown that the genuine reasons for the observation of zero crossover effect in the data recorded in transient electromagnetic survey using SQUID are actually attributable to the flow of the reverse current and its associated magnetic field generated by the transmitter loop. In this paper, we discuss the possible reasons for the observation of this zero crossover by various research groups, and present a detailed analysis of our own experimental data. • Negative decay or sign reversal occurred in SQUID based TDEM system. • Novel explanation for the sign reversal effect in TEM measurements • Tertiary currents responsible for negative decay not IP effect. • Concrete evidence for the tertiary current flow in Tx- loop for the sign reversal effect [ABSTRACT FROM AUTHOR]

In field seismic exploration, missing seismic traces is inevitably encountered due to the constraints of the exploration environment and equipment. Thus, seismic data reconstruction is essential for seismic exploration analysis. In this paper, an attention-based U-net (AU-net) architecture is proposed by incorporating the attention mechanism into the U-net structure to address seismic data reconstruction challenges. The network incorporates both channel and spatial attention modules. Experiments comparing the reconstruction results of U-net, DnCNN, curvelet, and AU-net demonstrate the robustness of deep learning methods in handing increased missing trace percentages. The AU-net achieves superior reconstruction effect on contiguous missing regions, and exhibits better generalization through transfer learning experiments. To facilitate network training, this paper introduces a novel data-slicing technique to split and merge rectangular data for reconstructing shot records. This approach can be applied to any network and has high practical value. • A novel framework is built based on U-net for seismic data reconstruction in which attention module was added. • Transfer learning experiments proved the reliability of the network. • A novel splitting and splicing method was used to improved the quality of reconstruction. [ABSTRACT FROM AUTHOR]

Rapid and high precision detection of coal-rock interface is one of the key problems in intelligent coal mining. In this paper, an air-coupled ground penetrating radar (GPR) antenna is developed for coal-rock interface detection in fully mechanized mining face, which can realize non-contacting, high precision, high-resolution detection during the mining process. The main features of the air-coupled GPR antenna are ultra-wideband, narrow beam, and high gain. For the vertical polarization pattern at 1200 MHz, the main lobe amplitude is 6.29dBi and the main lobe width (3 dB) is 108.3°, as well as the relative bandwidth of the antenna can reach 51%. For design validations, the novel air-coupled GPR antenna developed in this paper is tested in mine, the detection error and the average error percentage are ±1.2 cm and 8.6%, respectively, which shows the superior detection ability of the novel air-coupled GPR antenna and the applicability in complex geological environment, providing technical support for the identification of coal-rock interface in intelligent coal mining. • Development of a novel air-coupled radar antenna for coal-rock interface detection. • The non-contact detection with the antenna suspended in 30 cm off the target. • Application of the coal-rock interface detection in fully mechanized mining face. • The average error of coal-rock interface detection is ±1.2 cm (8.6%). [ABSTRACT FROM AUTHOR]

Road collapses pose dangerous threats to traffic safety in urban cities. Typically, these collapses result from under-road defects such as cavities, loose soil, and voids. With the development of multi-channel 3D ground penetrating radar (GPR) systems, GPR has become a routine method for inspecting the subsurface conditions of roads. However, the reflection characteristics of hidden defects in 3D GPR results have not been well studied due to the complexity of urban road structures. Consequently, accurately detecting all subsurface defects in GPR survey areas remains challenging. In this paper, numerical models of road structures with typical types of hidden defects are constructed, and their reflection characteristics in GPR B-scan profiles and C-scan depth slices are analyzed. Then, the field results obtained using a car-mounted 3D GPR system are presented to confirm the reflection characteristics of these hidden defects. Finally, the reflections of manhole covers and underground pipelines, which are the most prevalent forms of clutter in GPR images in urban environments, are compared with those of hidden defects. The findings of this paper will facilitate the accurate interpretation of field 3D GPR data for road inspections and the mitigation of road collapse accidents. • Reflection characteristics of typical under-road defects in 3D GPR images. • Numerical models of road structures with typical types of hidden defects. • Field case studies employing a 3D GPR system to detect under-road defects. • Comparison between under-road defects and other anomalies in 3D GPR images. • Under-road defects detection for mitigating road collapse accidents. [ABSTRACT FROM AUTHOR]

To analyze the hazard-causing modes of landslides, this paper proposes a three-dimensional discrete element model reconstruction method that employs an unmanned aerial vehicle survey and multi-electrode resistivity tomography method. To convert the resistivity profile into a material profile, we adopt the peak of the probability density method for material classification and utilize the Haar wavelet transform for image denoising. Subsequently, inverse distance weighting interpolation and the curtain-point method are used to transform two-dimensional profiles into a 3D visualization model. Similarly, the triangular mesh boundary can be extracted from the 3D visualization model using the curtain-point method. A mapping function f including the macroscopic parameters, was defined to populate the particles within the boundaries. Using the iterative method and defining the loss function L for parameter calibration, the targeted 3D discrete element model was constructed after setting the velocity threshold. This method was applied to the Changhe landslide (September 14, 2019) in Gansu Province, China, which had a typical damaged soil layer due to earthquake and rainfall factors. The results indicate that the lower part first exhibits significant displacement, followed by the upper and middle parts, which is consistent with the on-site inspections and UAV findings. • Peak of probability density method for material threshold division of resistivity is proposed. • Using weak attribute inheritance method to define boundary particle attributes. • Given a complete modeling process for discrete elements. • Apply the method to practical applications and verify the results. [ABSTRACT FROM AUTHOR]

Opposing coils transient electromagnetic method (OCTEM) adopts small and weak-coupling transmitting-receiving coils configuration, which helps to reduce side effect and improve the detection resolution. With such advantages, it has been widely used for shallow sub-surface target detection. However, when the method is used in urban area, measured data may be distorted by electromagnetic (EM) interference from nearby metal objects. In practical application, it is necessary to perform modelling to provide guidance for measuring data analysis. Two OCTEM application cases in detecting shallow sub-surface karst caves in urban area with metal objects nearby are presented in this paper. Corresponding modelling are carried out to study the interference effect of the nearby metal objects. The first application case is about the EM interference of a vertical steel tower, of which the influence distance reaches up to 9 m by modelling. The second application case is about the EM interference of a thin aluminum fence, of which the influence distance reaches up to 6 m by modelling. Only when the observation is outside the influence zone, the metal influence can be ignored. When the measurement is inside the influence zone, the metal influence cannot be ignored. However, as the nearby metal objects mainly affects the early data, the subsurface target may also be detected in condition that the target response is stronger than the metal interference, or the target response time window is wider than that of the metal interference. • EM interference from steel tower and metal fence to OCTEM have been simulated. • The nearby metal objects mainly affects the early OCTEM data. • OCTEM can be used in detecting shallow subsurface target. [ABSTRACT FROM AUTHOR]

At present, the detection of geological structural plane that give rise to rockburst is a complex problem. A large number of rockburst cases show that the geological structural plane influence the boundary of rockburst, especially the slip-type rockburst of structural plane. However, there is no set of comprehensive geological prediction methods at home and abroad for the detection of geological structural plane that give rise to rockburst, or low accuracy and high workload. Therefore, a method that can effectively detect geological structural plane is needed. Based on the analysis of regional engineering geological characteristics and geostress, this paper puts forward that based on the characteristics of rockburst cases in high geostress area and the rockburst prone to occur in the position with large geostress difference, the method of "combination of long and short geophysical prospecting method first, drilling and engineering geological analysis combination" is adopted to detect geological structural plane finely. The results show that: (1) Under the background of regional engineering geological survey and geostress inversion, the comprehensive geological prediction is carried out to detect the geological structural plane. The TSP has the detection accuracy of 10 m to meters, the ground penetrating radar has the detection accuracy of meters to decimeters, and the borehole imaging has the observation accuracy of centimeters. The combination of the three can multi-scale clearly reflect the distribution of geological structural plane compared with the previous single geological prediction. (2) Due to the complex distribution of surrounding rock mass interface and geological structural plane, the collapse phenomenon will also appear in the rockburst area on site, and the collapse causes a number of structural plane, which means that these structural plane becomes an important factor in slip-type rockburst of structural plane. In short, accurate detection of geological structural plane has certain reference significance for predicting the boundary of slip-type rockburst of structural plane and collapse. • The comprehensive geological prediction. • Detect the geological structural plane. • Predicting the boundary of the slip-type rockburst of structural plane and collapse. [ABSTRACT FROM AUTHOR]

Seepage hazards in dams remain a critical issue in flood control engineering. The pseudo-flow field method has shown high efficacy in detecting seepage points within dam structures. This paper delves into the core characteristics of the pseudo-flow field method, aiming to accelerate its detection speed in practical engineering contexts. By employing the Laplace equation for electric current, we established a numerical model to simulate the method's application in real-world scenarios. The simulation reveals the key characteristics of potential and current density distributions along measuring lines within the pseudo-flow field. Both horizontal and vertical measuring lines show a peak distribution of current density and potential near the seepage point, gradually diminishing towards the periphery. Conversely, vertical measuring lines further from the seepage point exhibit minimal changes, presenting a uniform distribution of current density and potential. The results confirm that the pseudo-flow field method can effectively detect seepage locations and that strategic placement of measuring lines can markedly improve detection speed. • The damage caused by leakage is extremely serious. • The accuracy of the pseudo-flow field legal leakage inlet is verified by numerical simulation. • The current density reflects more clearly on multiple leakage entrances • Perform horizontal measurement first to quickly eliminate or locate the leakage area, and then use vertical measurement to accurately locate the leakage location [ABSTRACT FROM AUTHOR]

The pressure stimulated current (PSC) signal emitted during the deformation and fracture processes of coal and rock materials holds significant importance for monitoring dynamic disasters in coal mines. However, the spatial response characteristics remain inadequately explored, posing significant challenges to the identification of risk-prone areas for underground dynamic disasters. To study the temporal and spatial response characteristics of PSC signal, the PSC response experiment in the failure process of raw coal under load was carried out, PSC signals from various spatial positions of coal were collected throughout the loading process. The results show that the sudden increase of axial PSC and the sudden decrease of transverse PSC appear with the sudden increase of acoustic emission (AE) hit rates, which is the main characteristic of the aggravation of coal internal fracture degree. The PSCs are closely related to the damage characteristics of the sample in terms of its corresponding position and drop time, which can better reflect the fracture concentration location of the coal sample. Building upon this foundation, the paper explained the internal factors contributing to variations in PSC spatial response characteristics of coal samples during load failure and emphasizes the inhibitory effect of crack development on PSC changes. • The variation trend of PSC signal corresponds well with loading process of coal. • There are obvious differences between axial and lateral PSCs. • The position of the mutation PSC corresponds to the damaged area of the coal. • The effect of coal crack on PSC variation is analyzed. [ABSTRACT FROM AUTHOR]

In the oil drilling process, drilling costs account for more than 50% of total E&P costs. High-voltage electric pulse rock breaking is an economical and effective rock-breaking method that has received widespread attention. At present, there is not much research on the influence of the shape of the electrode tip on high-voltage pulse rock breaking. This paper establishes a system of equations that control the electric breakdown field based on the changes in the electric field inside the rock. Then, using this model, we conducted simulation and laboratory experiments to understand how rocks break under different conditions, such as load voltages, electrode spacing, and electrode tip shapes. The results show that the volume of broken rock is directly related to the loading voltage. The best loading voltage range is between 200 and 220 kV. Increasing the spacing between electrodes helps break more rock, but if the electrode spacing is too large, it's hard to make a hole in the rock, and the rock won't break. An electrode spacing of around 35 mm is the best. The shape of different electrode tips directly affects the high-voltage pulse breaking effect. Hemispherical electrode tips are less favorable for rock breaking, while oval electrode tips are the best. The laboratory experiments and simulations give the same conclusions and verify the applicability and correctness of our model. This study aims to help design high-voltage electric pulse devices. • High-voltage electrical pulses effectively fracture deep hard rocks. • Multi-electrode configuration effectively enhances rock fragmentation efficiency. • Increasing voltage improves electrical rock fragmentation performance. • Greater electrode spacing results in larger volumes of fragmented rock. • The shape of electrode tips directly influences rock fragmentation efficiency. [ABSTRACT FROM AUTHOR]

This paper proposes a time-depth conversion accounting for discontinuities of the investigated buried scenario, which reverse in discontinuities of the propagation velocity of the waves. The focus is on the imaging of cavities in the framework of GPR prospecting. We show that a time-depth conversion accounting for the different propagation velocity of the waves in the cavity and in the surrounding soil can significantly improve the imaging in an easy way. Both simulated and experimental results will be proposed. • A combined time depth conversion is proposed. This mitigates compression effects for cavities. It also improves the slices. • The case of the cavities is exposed showing that a combined time depth conversion mitigates the compression effect associated with a customary processing. • Further on, the slicing becomes more realistic because the spatial reciprocal positions between cavities and further buried targets are quite better imaged. [ABSTRACT FROM AUTHOR]

The fluid identification of fracture media is susceptible to factors such as observation data, fluid sensitivity parameters, and inversion algorithms. However, appropriate nonlinear algorithms can be applied to reduce errors generated during the inversion process, thus helping to improve the reliability of fluid identification. In this paper, analysis and comparison are made to various reflection coefficient approximate formulas, of which the applicability and accuracy are demonstrated in fluid-saturated poroelastic media, and the objective function is constructed further from Russell's reflection coefficient formula. In this sense, the genetic algorithm (GA) can achieve the pre-stack inversion of seismic waves. Based on the inversion results such as P-, S-wave velocity, and density, the Russell fluid indicator, Poisson's ratio, and Poisson impedance are combined to identify the water-, gas-, and oil-bearing fracture. Finally, the applicability and reliability of the method are demonstrated through numerical calculations in some regions of Marmousi2 model and the field data. The results show that the seismic data can be preliminarily analyzed by the inversion method, followed by combining the Russell fluid indicator, Poisson's ratio, and Poisson impedance, effectively reducing the multiplicity of the inversion results and improving the reliability of fluid identification in fractured media. • Proper fluid factors can effectively reduce the multiplicity of inversion results. • The objective function is formed with Russell's reflection coefficient. • Combining three parameters can improve the reliability of fluid identification in fractured media. [ABSTRACT FROM AUTHOR]

Dehdan village lies downstream of Hattar Industrial Estate (HIE) that dumps industrial effluents into the nearby stream in Haripur Basin, Pakistan. In this paper, an integrated methodology such as borehole drilling, 1D and 2D geoelectrical measurements and hydrochemical anaylysis is suggested for assessing groundwater dynamics of the Dhedan area. A total of six boreholes were drilled to analyze aquifer sediments and to establish regional water table within the study area. Geoelectrical investigation emerges as an effective complementary technique that improved the data coverage and reduces the cost of borehole drilling, especially in the developing country. The geoelectrical datasets that consist of 1D and 2D sounding sites were acquired using the composite Wenner-Schlumberger configuration across the study area. The 1D-vertical electrical sounding (VES) data is utilized to infer subsurface rocks and to estimate hydraulic conductivity (S). The 2D-electrical resistivity tomographs (ERTs) each about 300 m long were also acquired across the highly contaminated Dehdan stream. Physicochemical and heavy metal analyses of twenty-three water samples collected from the stream water and the aquifer sediments were carried out to suggest potable water-quality in the region. A good correlation between the 1D resistivity data and borehole logs is established to investigate subsurface rocks down to 175 m depth. The results show presence of a shallow aquifer unit at about 17 m thick and relatively a deep aquifer layer at about 50 m depth. The hydraulic conductivity (S) identified moderate to good protective zones for contamination. The ERTs imaged contaminated highly conductive layer overlain by relatively resistive layers. Resistivity value for the highly conductive zone, about 25 m thick, is <11 Ωm. The ERT shows a localized shallow aquifer unit that is recharged by the contaminated stream water especially during rainy seasons. The 3D model based on the ERTs demonstrates that the resistivities within the low-resistivity anomaly remain unchanged and gradually increased downward. It was considered that these spatial changes in resistivities were related to dilution of stream highly-contaminated water with shallow aquifer sediments and the contamination migration downward to next aquifer unit across the stream. The hydrochemical analysis shows that four out of six analysed samples were highly polluted and the contamination level decreased at greater depths and as distance from the highly contaminated stream increases. A semi-confined to confined aquifer unit present at about 50 m depth contains relatively good quality water. This aquifer unit is highly encouraged for groundwater exploitation for human consumption. • An integrated approach to assess groundwater contamination, attributed to effluents of the Hattar Industrial Estate. • Borehole logs and geoelectrical data delineated groundwater aquifer units. • 2D ERT tomographs imaged contaminated aquifer unit. • Physiochemical and elemental analysis of water samples suggest majority samples are highly polluted. [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]

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]

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]

Inrush hazards like water and mud inrush can cause great loss of life and property, which should be predicted in advance during tunneling. To identify types of inrush hazards, investigating water-bearing condition and filling materials inside hazardous bodies is required. Thus, after detecting hazardous bodies by using methods like resistivity method, seismic method and transient electromagnetic method, more hydrogeological information is need to conduct further investigation of filling materials inside hazardous bodies. We aim to identify the types of inrush hazards by investigating the water-bearing condition of filling materials utilizing magnetic resonance sounding (MRS). We developed a methodology, through which hazardous bodies and the inside filling materials can be characterized by electrical resistivity, water content and MRS relaxation distribution. Based on multi-exponential scheme, we made a function, describing the distribution of MRS relaxation, to characterize the scale and uniformity of pore size. By numerical modelling of hazardous bodies that can cause water inrush, mud inrush and debris inflow, MRS responses corresponding to different types of inrush hazards were simulated. The results have shown that the MRS response can be affected by variations of electric resistivity, water content and MRS relaxation distribution resulting from the water-bearing condition related to different types of inrush hazards. Besides, by considering water content inside the surrounding rock, the influence of which is illustrated to be obvious in the area near the transmitting loop. In this paper, MRS have been proven as a capable and reliable technique to identify types of inrush hazards. The characterization of water-bearing condition in front of tunnel face and the modelling of hazardous bodies can be realized by using the method presented in this paper. • Magnetic resonance sounding. • MRS responses of typical hazardous bodies resulting in inrush hazards were stimulated. • Filling materials and its water-bearing condition of different types of inrush hazards were characterized utilizing distruibution of resistivity, water contents and relaxation time. [ABSTRACT FROM AUTHOR]

Electromagnetic induction is the most common technique used for geophysical survey of underground utilities, in planning stage, prior to construction/excavation and maintenance stage of underground's construction projects. Despite its popularity and usefulness, its reliability and accuracy are nevertheless always questionable due to coupling effects amongst the very congested underground utilities. This work studies the disturbed electromagnetic field patterns caused by the coupling effect of neighbouring cables and metallic pipes via a series of validation experiments in PolyU's indoor underground utility laboratory. The 'fingerprints' of electromagnetic fields are established corresponding to different below ground conditions. 11 setups with 260 tests were designed to study the coupling effect between a cable and a pipe. The results show that the coupling effect is significant in the active detection of the cable. The experiment also compares the accuracies of cable and pipe detection at different induction frequencies with reference to the accuracy levels in the HK EMSD requirement of competent person for power cable detection and PAS128:2014 British standard. This paper demonstrates the importance of coupling effects in the detection of underground utilities, which should be considered in future revision of standards. • Coupling effects of EM locating of underground utilities are never studied. • This paper is the first to evaluate such EM coupling effects amongst utilities. [ABSTRACT FROM AUTHOR]

In this paper, we extend the multichannel surface wave (MASW) analysis method for non-destructive testing (NDT) of medium to large diameter concrete pipe segments. In a typical MASW investigation, experimentally obtained surface wave records from an elastic medium are transformed into dispersion curves and compared with the appropriate theory to inversely determine the unknown parameters of the medium. We extend this procedure for the lengthwise and circumferential inspection of an individual concrete pipe segment by employing longitudinal and circumferential waves. These waves are generated by a point impact applied perpendicular to the pipe surface. Using finite element based simulations, it is first shown that the dispersion properties of surface waves traveling along two orthogonal cross-sections of a pipe segment, which intersect the impact point, agrees with the corresponding theoretical properties of longitudinal modes in an infinite hollow cylinder and circumferential Lamb wave modes in a circular annulus. This forms the basis for implementing the MASW method along the lengthwise and angular directions of the pipe, independently. Using the lessons learned from numerical study, an experimental demonstration of the proposed angular MASW implementation is carried out in a reinforced concrete pipe segment held under laboratory conditions. Equations for a cylindrical version of the phase-shift based wavefield transform given in [1] is presented for use in this process and its effectiveness to extract the angular phase velocity spectra from an actual record is demonstrated. Finally, it is shown that multi-modal dispersion curves can be extracted from an actual reinforced concrete pipe segment and its unknown elastic properties can be determined using the proposed method. The numerical models developed in this paper are validated by comparing its results against the measured data. • MASW analysis of elastic waves in medium to large diameter concrete pipe segments is conducted. • Dispersion curves of surface waves propagating along lengthwise and circumferential directions are extracted. • Elastic properties of a reinforced concrete pipe is determined from an experimentally obtained waveform record. • Finite element based numerical modeling is conducted and experimental validations are provided. [ABSTRACT FROM AUTHOR]

With the increasing depth of mining, the disasters of water inrush above confined aquifers tends to increase annually, which seriously threatens the safe mining of coal seam, especially the extra-thick coal seam floor in deep mining. This research is to study the characteristics of deformation and failure of extra-thick coal seam floor in deep mining, the field measurement is carried out by the distributed fiber optic sensing technology (BOTDR) and the 3D resistivity method of studying coal field in China. The axial strain curves and resistivity distribution characteristics of the mining face at different depth under the coal seam floor are obtained by extending the working face. Through the comprehensive comparison and analysis of monitoring data in the monitoring boreholes, the characteristics of deformation and failure of extra-thick coal seam floor in deep mining can be ascertained. The results indicate that the comprehensive monitoring technology can effectively distinguish the characteristics of stress excess, distortion and failure of rock during the process of the working face mining. The influence range of mining advance stress is about 36 m, the failure depth of coal seam floor is about 12 m and the depth of mining disturbance deformation is about 26 m. The formation of the deformation and failure of the coal seam floor have obvious stratification, which are mainly influenced by the formation structure and the lithology of the rock strata. The comprehensive monitoring technology can effectively capture the fine features of the deformation and failure of the coal seam floor, which is valuable for extra-thick coal seam floor in deep mining. • In this paper, the distributed fiber optic sensing technology is used for the first time to monitor the deformation and failure of the coal seam floor. • The coal seam studied in the paper is an extra-thick coal seam and the buried depth of the coal seam is large, belonging to the extra-thick coal seam in deep mining. • The high frequency of data acquisition and the long duration of acquisition, so as to realize the dynamic monitoring research on the deformation and failure of extra-thick coal seam floor in deep mining. [ABSTRACT FROM AUTHOR]

Abstract The accuracy of a numerical derivative has a significant effect on any numerical simulation. Long stencils can provide high accuracy as well as reduce the numerical anisotropy error. However, such a long stencil demands extensive computational resources and with their growing size, such derivatives may become physically non-realistic since contributions from very far offset whereas the derivative is local in nature. Further, the application of such long stencils at boundary points may introduce errors. In this paper, we present a very efficient, accurate and compact size numerical scheme for acoustic wave propagation using implicit finite difference operator, which utilizes a lesser number of points to estimate derivatives in comparison to the conventional central difference derivative operator. The implicit derivative operator, despite its several advantages, is generally avoided due to its high computational cost. Therefore in this paper, we discuss a method which can dramatically reduce the computational cost of this scheme to almost half. This strategy is useful particularly for 2D and 3D case. Spectral characteristics of the derivative operator and the numerical scheme are compared with several other central difference schemes. We have also demonstrated an application of this scheme for seismic wave propagation in 2D and 3D acoustic media. Highlights • Highly efficient 2D/3D implicit finite difference scheme of 10th order is presented. • The modified implicit scheme becomes almost twice efficient. • A comparison of explicit and implicit FD operator and resulting schemes is provided. • Application on a realistic model has been demonstrated. [ABSTRACT FROM AUTHOR]

Abstract This work proposes a new regularization strategy for the Full Waveform Inversion (FWI), a promising technique to generate images of the subsurface from seismic data. This problem is ill-posed and depends on the application of regularization strategies to minimize noise fitting. The most often used strategies are Total Variation and Tikhonov regularization, assuming that the solution has a certain degree of smoothing. The main objective of this paper is to propose the use of the Geological Incoherence Index - GII as a constraint for the inverse problem. The GII assumes that the values of velocities increase with depth, perpendicularly to the interfaces between layers. The main advantage of the GII regularization is that it does not change the search direction of the FWI without regularization. In the present work, the forward problem is modeled by the Helmholtz equation, and solved by the Finite Difference Method. The inverse problem is solved by a multi-scale strategy using the L-BFGS method. Computational experiments presented in this paper show that the use of GII leads the solution to a more geologically likely solution, providing more realistic images of the subsurface compared to the classic FWI, since it carries information of the sedimentary bedding. Highlights • New regularization strategy for inverse problems in geophysics. • The strategy called Geological Incoherence Index encompass geological features. • The proposed strategy gives better results than traditional approaches. [ABSTRACT FROM AUTHOR]

Abstract This paper utilizes the 3-array variation of the compressed sparse row (CSR) format to store upper triangular elements of coefficient matrix, and applies the Intel MKL PARDISO solver to solve large sparse linear systems of equations, when calculating the 3-D magnetotelluric (MT) fields using edge-based finite element (FE). By default, Intel MKL PARDISO stores matrices in RAM, namely in-core (IC) mode, however, it is quite memory consumption. One can specify that Intel MKL PARDISO stores matrices on disk, it is referred to as out-of-core (OOC) mode. But the OOC mode consumes longer time than the IC mode. We compare both time and memory consumption of IC and OOC mode via COMMEMI 3D-1A and 3D-2A models. As shown in the examples, the OOC mode can solve very large problems since the amount of main memory required is significantly reduced, in the acceptable computing time, which makes frequency loop parallelization of 3-D MT modeling possible on a small memory PC. Highlights • This paper developed an edge-based FE method for 3D MT modeling. • We introduced the out-of-core of PARDISO to enable the computation of 3D MT modeling in the small memory PC. • We used the 3-array CSR format to store the upper triangular non-zero elements of the large, sparse, symmetrical matrix. [ABSTRACT FROM AUTHOR]

Abstract For controlled source audio frequency magnetotellurics (CSAMT) which supported by traditional dipole hypothesis theory, the observations point should be located in far source zone. However, during field measurements, due to limited transmitter power, the distance between transmitter and receiver is usually not too large. Sometimes, field measurements are carried out in the near source zone, and the traditional dipole hypothesis will produce large errors under such condition. So, the errors between the approximate solution of traditional dipole approximation and the exact solution of the long grounded-wire source are firstly studied in this paper. Moreover, relative error distribution between exact solution of the long grounded-wire source and electric dipole source variations with different frequencies has been analyzed. It finds that the traditional dipole hypothesis bring large errors in the near source zone and no longer be satisfied to such condition. As a further study, a new 'harmonic point charge' solution for CSAMT, instead of the traditional dipole hypothesis, is proposed in this paper, which lay a foundation to realize near source prospecting and obtain more accurate near source responses in frequency domain electromagnetic. [ABSTRACT FROM AUTHOR]

Abstract Hydraulic fracturing plays a crucial role for economic production from unconventional resources. Especially development of shale gas resources is highly dependent on this evolving technology. Meanwhile, advanced logging tools, microseismic mapping and well testing analysis revealed the presence of abundant natural fractures and the complex induced fracture network in their presence. Natural fractures may open during fracturing treatments and change the direction of fracture growth. Despite the significance of natural fractures in formation evaluation, reservoir modeling, fracturing design and notable advances in numerical modeling of fractured reservoirs, these modeling require a description of natural fractures, which is often impossible to obtain from seismic. This paper proposes an innovative optimization technique to estimate the geometry of natural fractures based on geophysical data. A constrained mixed-integer nonlinear programming (MINLP) model is developed to compute and define possible optimal realizations of natural fractures from selected double-couple microseismic events, which will provide both geologist and reservoir engineers a robust tool for evaluating and modeling naturally fractured reservoirs. The objective of the MINLP problem was to minimize the total least squared errors of distance between microseismic events under different geodesic and technical design constraints. The performance and efficiency of the MINLP problem is tested through several instances. Computational results confirm to the expected numerical results obtained manually. An real example with field data is presented to show the model's computational capability. Highlights • Natural fractures may open during fracturing treatments and change the direction of fracture growth. • Despite significance of natural fractures, there is no available tool for description of natural fractures using microseismic. • This paper proposes an innovative optimization technique to estimate the geometry of natural fractures using microseismic data. • A constrained mixed-integer nonlinear programming is developed to compute possible optimal realizations of natural fractures. [ABSTRACT FROM AUTHOR]

Abstract In gravity surveys, many unwanted effects are produced by geological or non-geological sources. These calculable effects have to be removed through the data reduction procedure. Common corrections in gravity measurements are those for the instrument drift, the tide, the Free Air, the Bouguer and the terrain effect. However, when we deal with gravity campaigns carried out in cities, we also have to take into consideration the so-called Building Correction. This concerns the correction of the gravitational effect caused by the existence of buildings and anthropogenic constructions (stadiums, bridges etc.) close to a gravity measurement. This process can become quite demanding sometimes. Because of that, in this paper we discuss a calculation method for the Building Correction of the gravity measurements. Two types of data are crucial in that procedure. The first one is the mean building density and the other one is the volume of the existing buildings, which is related to the spatial distribution and the buildings height. The mean building density has been calculated in this paper, based on percentage contribution of the building materials (concrete, bricks etc.) of the whole building volume. The calculated mean building density was equal to 0.44 g/cm3. A Building Height Map has been produced, based on the Digital Elevation Model and the Digital Surface Model. Taking into account the building volume and their density, a simulation of the terrain correction procedure has been carried out, for the Building Correction calculation. The calculated Building Correction values range from almost zero (in the suburbs) to 0.25 mGal. A comparison for the Residual Anomaly values (affected by the Building Correction) has also been made. Differences up to 0.19 mGal revealed are considered to be quite significant for the credibility of the final data. Highlights • Building Correction: Calculation and application on gravity measurements. • Calculation of Building density. • Building Height Map (Building coverage & volume) • The importance of Building Correction for urban gravity survey. • Residual Anomaly differences before and after the application of the Building Correction. [ABSTRACT FROM AUTHOR]

Electromagnetic wave logging at the measurement frequency of megahertz provides two kinds of information namely conductivity and permittivity, which is helpful to solve the problem of identifying water flooding situation of oil layers after long-term water displacement development. The electromagnetic wave combination logging tool in Daqing Oilfield measures two phase difference curves at frequencies of 60 MHz and 2 MHz. At present, there is still a lack of permittivity and conductivity inversion methods for this tool that are suitable for the interpretation of water flooding situation. Based on the magnetic dipole theory of uniform medium, the study found that for the combination logging tool, the 60 MHz phase difference is affected by both the permittivity and conductivity of the formation, while the 2 MHz phase difference is mainly affected by the conductivity. The reasonable and conveniently procedure for calculating the permittivity and conductivity from the inversion of the phase difference curves is constructed. Firstly, the shale content and porosity parameters of the layers are calculated from the curves of natural gamma and acoustic time difference, while the permittivity is calculated by a formula linearly constrained by shale content based on the permittivity of mudstone and oil-bearing clean sandstone. Secondly, for 2 MHz phase difference curve, a formula for calculating conductivity with known permittivity is established. Thirdly, set the calculated permittivity as the known parameter, a formula for inversion of the 2 MHz phase difference curve to calculate the conductivity is derived. Fourthly, using the inversion calculation of the conductivity as a known input, establish a formula for inversion of the 60 MHz phase difference curve to calculate the permittivity. In the process, the permittivity calculated by the shale content constraint method is used as the initial value of the iteration, which weakens the influence of mudstone on the permittivity and ensures the accuracy of the iteration. Finally, the permittivity and conductivity calculated by inverse calculation for two sealed coring wells can reflect the flooding situation of layers. The identification standard of flooding levels was established by using the conductivity and permittivity of inversion calculation, and the coincidence rate reached 90.7%, which is suitable for the effective identification of remaining oil in the long-term fresh water displacement layers. At the same time, based on the simplified theoretical model, the inversion of 3 combination of (2 MHz, 20 MHz), (60 MHz, 20 MHz), (2 MHz, 100 MHz) is carried out respectively, and the calculated values of remaining oil saturation are consistent with the injected water sweeping area, so the universality of the research method is verified. • Paper proposes the algorithm for calculating the permittivity and resistivity parameters. • Paper proposes the processing flow for well data, which has good operability and practicability. • The calculated permittivity and resistivity can well reflect the remaining oil situation. • Process can realize the rapid judgment of the remaining oil saturation and water flooding levels. [ABSTRACT FROM AUTHOR]

In order to obtain high-quality electrical resistivity imaging (ERI) inversion results, this paper proposes a wavelet-based neural network inversion method. In addition, it is applied to 2D electrical resistivity tomography imaging. Firstly, a sample set suitable for wavelet neural network training is designed to optimize neural network parameters and improve the accuracy of electrical resistivity inversion. Secondly, a hybrid multi-layer wavelet neural network is designed, which uses Mexican-hat and Morlet wavelets as activation functions for different hidden layers, to improve the generalization ability and stability of the network. Finally, the superiority of the WNN is verified through two experiments and applied for inversion in field examples. The inversion results of the synthetic and field examples show that the introduced method is superior to other algorithms in terms of prediction accuracy and computational efficiency, which contribute to better inversion results. • In applying resistivity inversion, WNN can describe the outline of the abnormal body, and the inversion time is short. • This paper designs a sample set suitable for wavelet neural network training. • Two cases are used to verify the accuracy and superiority of WNN in resistivity inversion. • WNN is applied to practical engineering, and its accuracy is verified by core drilling sampling. [ABSTRACT FROM AUTHOR]

Surface depressions and subsurface defects have been a trendy topic in ground shaking problems. In the case of canyon tunnels and canyon pipeline projects, surface movement and cavity edge stress concentrations have been a concern in the design, and the effects of cracks need to be considered if the underground structure contains cracks. In this paper, the wave scattering problem in an elastic half-space medium containing semicircular depression(canyon), cylindrical cavity and crack is investigated by using theoretical methods, the wave function expansion method, the complex function method and the mirror image method to solve the control equation in the form of Helmholtz equation satisfying the zero-stress boundary condition, and the corresponding displacement function is solved. The Green function method and the crack "cutting" technique are used to construct cracks. The unknown coefficients in the system of equations to be determined are solved by free boundary conditions combined with Fourier expansion. The displacement field is a superposition of appropriate wave fields. Finally, the effects of the relevant parameters on ground motion | w | (w), dynamic stress intensity factor (DSIF) of the tip of crack and the dynamic stress concentration factor (DSCF)of the cylindrical cavity were investigated by frequency and time domain analysis. This study not only provides a theoretical basis for practical unlined tunnels or pipeline projects, but also provides a basis for the seismic design of underground structures. • The model in this paper is closer to the actual situation of canyon underground engineering, and the study of this situation is helpful to save resources and guarantee life safety. • The time-domain results of each point can be used to analyze the transient response of underground structures or surface structures, providing theoretical support for structural strength design. • The research on the existence of underground cracks provides a certain theoretical reference for reducing hidden safety problems in the implementation of practical projects. [ABSTRACT FROM AUTHOR]

Porosity estimation is one of the essential issues in oil and natural gas industries to evaluate the reservoir characteristics properly. Therefore, it is imperative to predict porosity with the optimum way to reduce logging tests. In this paper, fuzzy logic (FL) and neural networks (NNs) are considered effective approaches to predict the Lower Goru sand reservoir's porosity curve. The input dataset for the study contained four known logs, gamma ray (GR), neutron porosity (NPHI), density (RHOB), and sonic (DT) of five wells drilled. For the fuzzy logic model, ten bins were used. The closeness of fit (Cfit) curves were computed using the most likely and second most likely curves. The weighted average final probability Pi, or the most likely solution, was also calculated. The curve histogram distribution and set of curve bin distribution cross plots were built using a fuzzy model. In the fuzzy logic model, the Gaussian membership function provided the optimum match for the examined geophysical log data. Fuzzy logic models indicate Cfit values ranging from 94 to 100% for Sawan-01, Sawan-02, Sawan-03, Sawan-07, and Sawan-08, with standard deviations of 1.248, 1.241, 1.254, 1.336, and 1.374, respectively. The neural networks model was trained using the backpropagation (BP) algorithm. The neural networks model has a Cfit_nn of 88%–100% across five wells with standard deviations of 0.016, 0.014, 0.015, 0.017, and 0.018. The results show that the predicted modeling evaluations using fuzzy logic and neural networks techniques fit the geophysical log data quite well. The multiple linear regression (MLR) assessments were conducted using the same geophysical log datasets of five studied boreholes for comparison. The coefficients of determination (R2) for the fuzzy logic (PHIT_ml) and neural networks (PHIT_nn) models were 0.960127, and 0.973039, respectively, whereas the values of the PHIT curve for multiple linear regression (PHIT_mlr) 0.926329. The high R2 values show that fuzzy logic and neural networks are more effective methods for PHIT curve prediction than the multiple linear regression approach. The relevant correlation was derived by comparing synthetic log values to actual log values. The evaluations between recorded and predicted values applying the two distinct approaches fuzzy logic and neural networks revealed that both are effective at synthesizing PHIT logs. The confirmation of this efficiency was further verified by the low values obtained in the root mean square error (RMSE) analysis. The study conducted on the Sawan Gas Field wells revealed that both fuzzy logic and neural networks are reliable approaches for predicting the PHIT curve. By using a composite of GR, RHOB, NPHI, and DT logs, these techniques can provide a realistic fit for both actual and synthesized PHIT curves. The findings of this study suggest that the implementation of these methods can contribute to the improvement of hydrocarbon exploration and production in the region by reducing uncertainty in predicting the PHIT curve. Moreover, the methods used in this study have the potential for wider application beyond the Sawan Gas Field. These methods can be applied globally to predict the PHIT curve and evaluate the reservoir prospects. The successful application of fuzzy logic and neural networks in this paper provides a solid foundation for future research on using machine learning techniques in reservoir characterization and modeling. • FL and NNs showed potential in assessing complex conditions for porosity prediction in the Lower Goru sand reservoir. • FL and NNs provide better results than MLR approach. • In the FL model, the Gaussian membership function provided the optimum match for the examined geophysical log data. • FL and NNs effectively synthesize PHIT logs based on evaluations of real and predicted values. [ABSTRACT FROM AUTHOR]

Ultrasonic compressional (P -wave) and shear (S -wave) velocity data, obtained from a set of 35 dry and water-saturated (carbonate) core samples, were presented as a first part to this study, in a separate paper by Bakhorji and Schmitt (2022). These carbonate samples were obtained from a prominent reservoir in Saudi Arabia. In this follow-up paper, the velocity measurements, obtained from these 35 core samples, were utilized to, firstly, predict and validate four appropriate rock physics models and to, secondly, derive empirical relationships relating the P - and S -wave velocities to the porosity and calcite content of the samples (over the effective pressure range from 5 MPa to 25 MPa). The derived empirical relationships were validated against the wireline P - and S -wave velocities assuming insitu reservoir pressure conditions. The empirical models predicted the P - and S -wave velocities accurately over the reservoir interval of interest. The shear strengthening / weakening effect, or the saturation effect on the shear moduli, was also modelled and is discussed further. The comparisons of the Biot, Gassmann, Mavko-Jizba-Biot (MJ-Biot) and Mavko-Jizba-Gassmann (MJ-Gassmann) model predictions, with the measured water-saturated P - and S -wave velocities, show that the squirt mechanism was not applicable for our samples. The Gassmann model consistently over-predicts the water-saturated S -wave velocities at low pressure, but closely fits the measured velocities at high pressures, whereas Biot over-predicts the water-saturated velocities in most of the studied samples. We conclude that Biot global-flow is most likely to be the principle dispersion mechanism in these samples. • Validated the applicability of Gassmann and Biot's high-frequency models in Carbonate. • Derived empirical models relating velocities to the porosity and calcite content. • The derived empirical models accurately predicted the velocities. • Verify the flow mechanism affecting the ultrasonic measurements on the samples. • It appeared that Biot global flow was occurring in these samples. [ABSTRACT FROM AUTHOR]

The shear wave (S-wave) velocity plays a crucial role in interpreting the lithology in seismic data, identifying fluids and predicting reservoirs. However, S-wave velocity is often unavailable due to the high cost of measurement and technical constraints. Conventional methods exhibit limitations that potentially impact the accuracy or efficiency on predicting S-wave velocity. Moreover, these methods always ignore the uncertainty quantification associated with the predicted results. This paper proposes a sparse Gaussian process regression (SGPR) method to predict the S-wave velocity in tight sandstone reservoirs. SGPR is a highly efficient regression technique that is based on the Gaussian process regression (GPR) method. In the SGPR method, inducing inputs are introduced to approximate the kernel matrix to decrease the computational complexity. A sparse set of inducing inputs and kernel hyperparameters are optimized through minimizing the Kullback-Leibler (KL) divergence between the exact posterior distribution and the approximate one. In this study, we select several types of logging data, which include porosity, water saturation, shale content, lithology and P-wave velocity, as the inputs for the SGPR method to predict S-wave velocity. To validate its effectiveness, we use the SGPR method to predict S-wave velocity in tight sandstone and compare the results with those from the GPR method, the bidirectional long short-term memory (BiLSTM) method and the Xu-White model. Additionally, we conduct cross-validation to demonstrate the robustness of the SGPR method. Our findings indicate that the SGPR method presents better performance and significant advantages about the accuracy and efficiency. Moreover, the SGPR method offers uncertainty quantification for the predicted S-wave velocity. • A sparse Gaussian process regression (SGPR) method is proposed to predict the S-wave velocity in tight sandstone reservoirs. • The SGPR method presents advantages in prediction accuracy, especially in computational efficiency. • The SGPR method offers uncertainty quantification for the predicted S-wave velocity. [ABSTRACT FROM AUTHOR]

Formation overpressure seriously affects drilling and downhole operation. Accurate prediction on the formation pore pressure can not only reduce the probability of drilling accidents, but also quantitatively evaluate the original formation pressure of underground pore space, which provides an important reference for site selection of carbon sink projects using underground space resources such as CO 2 geological storage. It is therefore necessary to set up a widely applicable method that is based on rock physics theory and conforms to the characteristics of rock mechanics and fluid mechanic. This method is suitable for both logging prediction and seismic inversion of pore pressure. The traditional method of predicting pore pressure based on P-wave velocity has multiple solutions, and the prediction based on S-wave velocity which is not sensitive to fluid has new significance. Based on the Hertz-Mindlin petrophysical model that considering pressure variation and the Gassmann fluid substitution equation that addresses the change in fluid saturation, this paper firstly derived rock physical formulas for predicting pore pressure in logging, and then derived the intrinsic power function relationship between the effective pressure (P e) and S-wave velocity (V s) as well as S-wave impedance (I s). Based on this, a set of geophysical methods integrating S-wave velocity prediction, pore pressure prediction in well and seismic inversion is finally established. The efficacy of this method has been well validated, with an average error of 2.35% in S-wave velocities prediction, 4.5% in single-well pore pressure prediction. The results of seismic inversion of pore pressure are consistent with the phenomenon of overpressure development in actual working area. This method can be further extended to other areas, providing invaluable reference for underground operation such as oil and gas exploration and CO 2 geological storage. • Based on Hertz-Mindlin model and Gassmann's equation, a petrophysical method for predicting pore pressure with well data is proposed. • The petrophysical relationship between S-wave velocity (V s), S-wave impedance (I s) and pore pressure is established to avoid the uncertainty of using P-wave to predict pore pressure. • The average error of S-wave velocity and pore pressure predicted by the method is 2.35% and 4.5% respectively. • The relationship between pore pressure and V s and I s established by logging is further applied to seismic inversion to realize the prediction of seismic pore pressure. • This method can be further extended to other areas, providing invaluable reference for underground operation such as oil and gas exploration and CO 2 geological storage. [ABSTRACT FROM AUTHOR]

Attenuation is a main factor limiting the resolution of seismic data. Earth works as a low-pass filter, which has strong attenuation of the high-frequency data. The loss of high-frequency energy can be compensated by the inverse Q filtering strategy. However, this method will also increase the energy of random noise which limits its application. The inverse Q filtering algorithm also needs the Q-factor as the input parameter, which is not easy to obtain. In this paper, we proposed a three-stage process to correct the attenuation of poststack data. In the first stage, a robust structure-oriented filtering is applied to remove random noise while protecting the structure information to avoid high-frequency noise burst. In the second stage, the local centroid frequency shift (LCFS) method is used to estimate the Q factor along the seismic trace. This method combined shaping regularization and centroid frequency shift (CFS) method to improve the robustness and accuracy of Q estimation to some extent. The final stage is to apply a stable inverse Q-filtering. Synthetic and field data examples demonstrate that time-varying Q-value can be accurately estimated by using the local centroid frequency shift (LCFS) method, and the proposed workflow can compensate the attenuation without bursting of high-frequency random noise. • A three-stage workflow is proposed focus on high SNR data to compensate attenuation avoiding random noise bursting. • A LCFS method is used to estimate time-varying Q-value. • A robust structured-oriented filtering is used to remove random noise. [ABSTRACT FROM AUTHOR]

Road underground defect detection plays a crucial role in assessing transportation infrastructure. Ground penetrating radar (GPR) serves as a widely used geophysical tool for this purpose. However, the traditional manual interpretation of GPR images heavily relies on the experience of the practitioner, leading to inefficiency and inaccuracies. To tackle these challenges, this paper proposes an automatic detection method for underground defects of roads based on an improved YOLOv5s model. First, the dense connection structure is integrated in the C3 module of the backbone to form the Dense-C3 module to enhance the capability of feature extraction. Subsequently, a convolutional block attention module (CBAM) is incorporated after each Dense-C3 module to refine features and enhance efficiency. Furthermore, the focal loss function is employed for the confidence loss to mitigate the impact of sample imbalance on detection performance. Experimental results demonstrate that the proposed model achieves a mean average precision (mAP) of 96.4% for synthetic data and 91.9% for real data, outperforming seven other models. The detection speed of the proposed model for real data reaches 51 frames per second, meeting the real-time detection requirements of road underground defects. • The Dense-C3 module is constructed to improve the feature extraction ability. • The CBAM is added after each Dense-C3 module to refine features. • The focal loss function is used to mitigate the impact of sample imbalance. [ABSTRACT FROM AUTHOR]

The oilfield's further fine development is significantly impacted by the interlayer of calcareous sandstone. Projecting the lateral distribution of subterranean calcareous sandstone is crucial for determining sequence boundary division, reservoir quality, and even CO 2 storage. Research on the sensitive characteristics of calcareous sandstone is still lacking. This study computes the percentage of lithologic difference and performs an intersection analysis of rock physical properties. It is found that Young's impedance, Poisson's ratio, and S-wave modulus have pleasurable sensitivity to distinguish calcareous sandstone. On the basis of this, a new sensitive factor for calcareous sandstone was built. The traditional approximate YPD reflection coefficient equation is only applicable to the weak contrast interface, and the accuracy is limited. This difficulty is solved in this paper by deriving a new equation for the nonlinear reflection coefficient. The equation is expressed by Young's modulus, Poisson's ratio, S-wave modulus, and density. Finally, the broadband nonlinear inversion method is adopted to provide a reasonable low-frequency model for the inversion of parameters. This allows for the realization of a stable inversion of parameters. The simultaneous broadband nonlinear inversion of Young's modulus, Poisson's ratio, and S-wave modulus provides a novel approach for calcareous sandstone prediction. We tested the accuracy and rationality of the method with both synthetic and field data examples. • Building a new sensitive factor of calcareous sandstone. • Deriving a novel nonlinear YPDS equation expressed by Young s modulus, Poisson s ratio, S-wave modulus and density. • The prediction of calcareous sandstone is realized by the broadband nonlinear inversion method. [ABSTRACT FROM AUTHOR]

The definition of lithology in oil wells by means of multiple geophysical analysis profiles an important role in the reservoir characterization process. From this one can generate lithologic models which in turn will be filled in with the petrophysical properties and can then be used in flow simulators to understand and study the behavior of an oil field. The identification of lithology can be accomplished by direct and indirect methods, but these procedures are not always feasible because of the cost or imprecision of the results generated. Consequently, there is a need to automate the process of reservoir characterization and, in this context, computational intelligence techniques appear as an alternative to lithology identification. In this paper balancing strategies are implemented in order to tackle the lack of data due to the characteristics of the distinct diagenetic processes. Six machine learning methods combined with data balancing techniques and a model selection approach to classify geologic data from the South Provence Basin. The results show the balancing strategies improve the overall performance of all classifiers and the model selection allows or obtaining the best parameters from a user-defined set. The computational tool developed in this paper arises as an alternative to assist geologists ans specialists in the task of reservoir heterogeneities identification. [ABSTRACT FROM AUTHOR]

Due to their complex structure and the difficulty of collecting data, the hydrogeology of basaltic islands remains misunderstood, and the Galapagos islands are not an exception. Geophysics allows the possibility to describe the subsurface of these islands and to quantify the hydrodynamical properties of its ground layers, which can be useful to build robust hydrogeological models. In this paper, we present seismic refraction data acquired on Santa Cruz and San Cristobal, the two main inhabited islands of Galapagos. We investigated sites with several hydrogeological contexts, located at different altitudes and at different distances to the coast. At each site, a 2D P-wave velocity profile is built, highlighting unsaturated and saturated volcanic layers. At the coastal sites, seawater intrusion is identified and basal aquifer is characterized in terms of variations in compressional sound wave velocities, according to saturation state. At highlands sites, the limits between soils and lava flows are identified. On San Cristobal Island, the 2D velocity profile obtained on a mid-slope site (altitude 150 m), indicates the presence of a near surface freshwater aquifer, which is in agreement with previous geophysical studies and the hydrogeological conceptual model developed for this island. The originality of our paper is the use of velocity data to compute field porosity based on poroelasticity theory and the Biot-Gassmann equations. Given that porosity is a key parameter in quantitative hydrogeological models, it is a step forward to a better understanding of shallow fluid flows within a complex structure, such as Galapagos volcanoes. [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]