We present a comprehensive geophysical methodology that combines magnetotelluric (MT), gravity and/or seismic data in a joint 3-D inversion framework to reduce interpretational uncertainty and provide a more accurate subsurface image of volcanic and geothermal systems. The methodology leverages the complementary sensitivities of each dataset—electromagnetic data for electrical conductivity, gravity for density contrasts, and seismic for velocity variations—to characterize subsurface structures more robustly than any single method alone.
As a demonstration, we apply this integrated workflow to Newberry Volcano in central Oregon, an important target for geothermal development and Enhanced Geothermal System (EGS) research. Broadband MT and gravity data were inverted jointly and integrated with existing seismic models. The integrated inversion/interpretation confirms a prominent conductive feature beneath the volcano’s southern rim and flank (SRFF), which is also marked by low density and slower seismic velocities. This feature extends from the southern caldera floor near the 1,300-year-old Big Obsidian Flow (BOF) to depths beyond 4 km, yet remains disconnected from the sub-caldera magma body.
Through this Newberry Volcano example, we illustrate how a multi-parameter approach provides improved resolution of the subsurface architecture and fluid flow pathways, highlighting the critical role of joint inversion in unraveling complex volcanic systems. The results not only shed light on Newberry’s hydrothermal alteration and fluid pathways but also underscore the broader applicability of our integrated methodology in guiding geothermal exploration and de-risking subsurface resource assessments.
How to cite: Tu, X., Schultz, A., and Di, Q.: Integrated MT, Gravity, and Seismic Inversion and Interpretation for Improved Subsurface Imaging, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2763, https://doi.org/10.5194/egusphere-egu25-2763, 2025.
Mine tailings storage is a major challenge for the mining industry due to the risks associated with contaminated mine drainage. Tailings can contain sulfides that, when exposed to atmospheric oxygen and precipitation, generate acidity that can spread downstream from tailings storage facilities. To mitigate this issue, the construction of multi-layer cover systems designed to divert infiltrating water from the tailings represents a promising solution. However, such cover systems are susceptible to deteriorate over time, and their effectiveness must therefore be regularly assessed.
Unlike traditional destructive methods, non-invasive geophysical techniques offer a rapid and cost-effective solution for analysing these cover systems. However, each geophysical technique has its own limitations when used individually. In particular, the ERT-IP (Electrical Resistivity Tomography and Induced Polarization) and MASW (Multi-channel Analysis of Surface Waves) methods can be used to characterize the volumetric properties of soils, such as variations in electrical resistivity and seismic velocities, but often lack the precision to delineate fine interfaces clearly. GPR (Ground Penetrating Radar) and seismic refraction, on the other hand, offer a better resolution for identifying the boundaries between layers but have difficulty in accurately describing the physical properties in volume.
This project aims to demonstrate the potential of a multimethod approach that combines these techniques by jointly analyzing the results to leverage their respective advantages while overcoming individual limitations and biases. Ultimately, the goal is to develop a joint inversion methodology to further refine the imaging of multi-layer cover systems, which are generally shallow and are made from a large range of materials.
This study presents the results from a field campaign conducted on a tailings storage facility where inclined multi-layer cover systems have been constructed to limit water infiltration (~1 m thick). Two longitudinal profiles were analyzed at two different scales. A high-resolution profile (32 m-long, 7% slope), with 64 collocated geophones and electrodes spaced by 50 cm intervals was used to focus on fine-scale variations in the cover layer system. Measurements were taken before, during, and after an infiltration test. A longer profile (100 m-long), with 64 collocated geophones and electrodes spaced by 1 m covered two instrumented sections (a 7% slope and a 28% slope) to provide a larger-scale view and greater depth of investigation. The ERT-IP data (collected using the Wenner protocol) and seismic data were coupled with GPR profiles conducted in continuous mode using 200 MHz and 1500 MHz antennas. All geophysical datasets were surveyed to allow comparison between techniques.
The results are interpreted jointly, in order to exploit the interface detection capabilities of GPR and refraction techniques along with the volumetric characterization provided by ERT and MASW at two different scales, which could improve the applicability of geophysical methods to assess the in situ performance of multi-layer cover systems installed on tailings storage facilities across larger scales.
How to cite: Impinna, T., Dimech, A., Fabien-Ouellet, G., Bussiere, B., Bedoui, L., and Boulanger-Martel, V.: Geophysical Multimethod Joint Analysis for Assessing Multi-Layer Covers on Mine Tailings at Two Different Scales, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20337, https://doi.org/10.5194/egusphere-egu25-20337, 2025.
As shallow mineral resources continue to deplete, deep mineral exploration has emerged as an essential trend in the mining industry. One of the most direct and effective methods to enhance exploration depth is by increasing the spacing of the current electrode in the array. However, this increase often results in a stronger electromagnetic (EM) coupling effect, which can significantly interfere with the induced polarization (IP) signal. To address these challenges, this paper calculates the EM coupling effects of various measuring arrays in both uniform half-space and layered media using analytical methods. Based on these calculations, we further analyze the impact of various factors on the intensity of EM-coupling interference in the layered media model, including the type of measuring array, the spacing of the current-electrodes, as well as the resistivity and frequency. Ultimately, based on the differences in the phases of the IP and the EM-coupling in the frequency domain, we derive the calculation formula of the relative phase method and analyze its decoupling effect at various application scenarios. The results indicate that an increase in the spacing of the current electrode, a decrease in ground resistivity and an increase in working frequency will significantly enhance the intensity of EM coupling interference. Under consistent conditions and detection depths, the EM coupling interference is typically greater for Schlumberger array compared to pole-dipole array. By employing the relative phase method, the biggest working frequency of the pole-dipole array can be enhanced by a factor of four, while the Schlumberger array can experience an increase of 10 to 11 times. It demonstrates that the relative phase method has a certain effect for removing the EM-coupling in large-depth IP exploration. The research provides significant guidance for the field implementation of large-depth IP exploration.
How to cite: Qin, H., Chen, R., Ji, Z., and Wang, Q.: Electromagnetic coupling analysis and removal in large-depth induced polarization method by using the relative phase, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1815, https://doi.org/10.5194/egusphere-egu25-1815, 2025.
The induced polarization (IP) parameters, such as the peak relaxation time and polarizability, have the potential to characterize pore structures of geomaterials and can be further used to distinguish lithology. However, the systematic experimental research on the IP response of carbonate rocks is scarce. To fill this gap of knowledge, we investigated the complex resistivity of 16 carbonate rocks, including dolostone and limestone, and discussed the applicability of existing induced polarization mechanisms for carbonate rocks. The relationship between IP parameters and pore structures were further analyzed by the experiment on variable confining pressure. The results indicate that the carbonate rocks with intergranular micropores or microfractures exhibit observable induced polarization response, where the amplitude and phase of complex resistivity are frequency-dependent, and still exist under high pressure conditions. Dolostone is characterized by low resistivity, high peak relaxation time, low polarizability, and the bell-shaped phase spectrum. Moreover, Stern layer polarization can explain the positive correlation relationship between peak relaxation time and pore size in samples with intercrystalline micropores. In contrast, membrane polarization provides a mechanism for the larger peak relaxation time in samples with microfractures, which is related to the low pore aspect ratio.
How to cite: Ma, M., Zhao, J., Yan, B., Zhang, Y., Sun, Y., and Ouyang, F.: Experimental Study on the Induced Polarization of Carbonate Rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8112, https://doi.org/10.5194/egusphere-egu25-8112, 2025.
Based on the mechanism of current density formation under natural electric fields and artificial stable current sources, this study proposes a multi-physics coupling theory involving seepage fields, ion diffusion fields, and stable electric fields induced by leakage. Coupling equations and boundary conditions for electric and magnetic fields were formulated based on fundamental laws of Ohm’s law and Biot–Savart law. A finite element-infinite element numerical simulation method was used to achieve three-dimensional response characteristics of coupled electric and magnetic fields in embankment leakage scenarios by incorporating conversion relationships for the water content, resistivity, and ion concentration. Based on the distribution characteristics of coupled electric and magnetic fields, a detection technique for locating leakage channels in embankment dam was proposed. This technique enhances leakage channel signals by applying an artificial stable electric field on both upstream and downstream sides of the channel. Subsequently, precise localization of leakage risks is achieved by observing two components of the coupled electric field or three components of the magnetic field on the dam surface. This new method was applied to locate the leakage channel at a pond in Hangzhou. The detection results have been validated by the drilling results, which demonstrated that this technique offers higher precision and better detection performance compared to traditional high-density resistivity methods. This work validate the effectiveness of the coupled electric and magnetic field-based detection method and provide a novel solution for embankment leakage detection.
How to cite: Liu, S., Chen, H., Deng, J., He, S., Wang, S., and Chen, Y.: Research on localization technology for dam leakage channels based on coupled electric and magnetic fields, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14405, https://doi.org/10.5194/egusphere-egu25-14405, 2025.
In the past decades, electromagnetic (EM) logging while drilling (LWD) has been widely used for well landing and geosteering in high angle and horizontal wells. Recently, this technology has been extended to geo-stopping applications in vertical wells and deviated wells, leveraging its excellent look-ahead-of-bit capability, particularly in ultra-deep reservoirs. Compared to traditional look-around applications in horizontal wells, achieving look-ahead capability is significantly more challenging because the sensitive region of the tool's response is primarily concentrated in the formation between the transmitting and receiving coils. Current look-ahead methods typically use the information from the drilled formation as a constraint to invert the formation ahead of the bit. However, this approach heavily relies on the accuracy of the surrounding formation property measurements. Therefore, to enhance the look-ahead capability and accuracy, it is necessary to further improve the contribution of the formation ahead of the bit to the tool's response.
In this paper, we analyze the spatial sensitivity of the magnetic field components based on the Born geometric factor. Among these, the coaxial (Hzz) and coplanar (Hxx and Hyy) components exhibit look-ahead sensitivity and can be used for look-ahead detection. In EM LWD look-ahead measurements, it is common to combine the coaxial and coplanar components to define the look-ahead signal. We further derive the spatial sensitivity functions for phase shift and amplitude ratio, with results showing that the primary contribution to the look-ahead signal still comes from the formation between the transmitter and receiver. To address this, we propose a signal enhancement method based on Multi-TR-spacing signal superposition. By exploiting the differences in sensitivity ranges of signals from different TR spacings, the method optimizes the sensitive space through signal superposition, thereby improving the tool’s look-ahead performance. Finally, we employ numerical simulation algorithms to compare the look-ahead capability of the new method with traditional methods. Simulation results demonstrate that, the look-ahead signal obtained with the new method is significantly enhanced to 1.5 times, and the maximum distance range has been increased by 30% that enabling the detection of interfaces at greater distances. Additionally, the new method results in a stronger sensitivity to the formation boundaries ahead of the bit, suggesting an improvement in inversion accuracy. It is important to emphasize that the method proposed in this paper can also be extended to look-around detection, for further enhancing the sensitivity of a specific detection area.
How to cite: Liao, X., Wu, Z., and Yue, X.: Sensitivity Analysis and Optimization for Enhancing the Look-Ahead Capability of Electromagnetic Logging While Drilling Tools, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5673, https://doi.org/10.5194/egusphere-egu25-5673, 2025.
With the intensifying exploration and development of deep and unconventional oil and gas reservoirs, the advanced prediction of the formations during drilling plays a pivotal role in mitigating drilling risks and optimizing drilling parameters. This technique serves as a crucial foundation for enhancing drilling trajectory accuracy and reducing operational costs. Currently, ultra-long spacing and low-frequency technologies enable the look-ahead, ultra-deep electromagnetic (EM) logging-while-drilling (LWD) tool to detect the top of the target formation more than 30 meters ahead of the bit. However, the measurement signal is predominantly influenced by the stratigraphy surrounding the instrument, resulting in a very low proportion of the spatial contribution in front of the bit. Consequently, the inversion process, which is integral to look-ahead detection, poses challenges for real-time geosteering.
To tackle this challenge, this study introduces a novel multi-spacing interleaved compensating antenna design aimed at augmenting the electromagnetic scattering field signal share at the forward stratigraphic interface. The spatial distribution of the new look-ahead detection signal is characterized using geometric factor theory. Additionally, the response characteristics and look-ahead detection capability of the proposed scheme are simulated and analyzed based on a response fast forwarding algorithm. The integral geometry factor associated with the novel look-ahead measurement effectively excludes contributions from the stratigraphy in the vicinity of the instrument, thereby enhancing the proportion of the look-ahead signal. This advancement is particularly beneficial for look-ahead detection. Simulations based on a single interface model reveal that the response diminishes to zero when the instrument is positioned at a considerable distance from the interface, whereas it attains non-zero values as the tool approaches the interface. In addition, the polarity of the response depends on the difference in resistivity between the two sides of the interface, which offers a more intuitive interpretation compared to existing methodologies. Furthermore, variations in magnetic field attenuation across different spacings leveraged to optimize spacing and signal synthesis combinations, further bolstering the capability of look-ahead detection. Numerical results demonstrate that the new method significantly improves the look-ahead detection capability of phase difference measurements compared to existing methods, with a maximum look-ahead depth of detection (DOD) increased by approximately 50%. The look-ahead DOD of amplitude ratio signal is comparable to that of existing methods.
In summary, the proposed method provides a more intuitive response to resistivity anomalies ahead of the bit, reducing the update time for forward geostructural information and enabling improved look-ahead detection. This innovation will provide a more cost-effective drilling solution for proactive risk avoidance in straight or low-angle wells and optimize casing shoe placement and coring operations.
How to cite: Wang, Y., Wang, L., Fan, Y., Ge, X., Yue, X., and Liu, T.: A New Compensated Design of Deep-reading Look-ahead Method in Electromagnetic Logging-while-drilling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14438, https://doi.org/10.5194/egusphere-egu25-14438, 2025.
The semi-airborne transient electromagnetic (SATEM) method has attracted increasing attention for its efficiency in various exploration scenarios. A recent geophysical survey in northern Gansu, China, employed the SATEM system to investigate the potential distribution of Volcanogenic Massive Sulfide (VMS) deposits. Several observed data profiles showcase significant late-time negative values, which were attributed to induced polarization (IP) effects associated with VMS minerals, as prior time-domain IP (TDIP) measurements revealed their high polarizability characteristic in such regions. More recently, interest in interpreting TEM data with IP effects has notably increased in the geophysical community as these effects can significantly disturb the data, leading to misinterpretation using the conventional resistivity-only (RO) inversion approach. Guided by the Cole-Cole model, which quantitatively describes the IP effect of materials using DC resistivity and other three IP parameters, numerous previous inversion studies have been successfully conducted to extract multiparametric information.
In this work, one field data profile is demonstrated in Figure. 1a and was inverted using a quasi-2D hybrid constrained inversion algorithm including three terms: (1). The classical data misfit functional; (2). Laterally smoothing regularization; (3). Fuzzy c-means (FCM) clustering regularization, which can facilitate the integration of the prior geophysical information. Local geological investigations suggest that VMS targets are primarily deposited in intact fracture spaces, which offer favorable conditions for mineralization and storage. The inversion results, shown in Figure. 1b, display clearly high-to-moderate resistivity interfaces surrounded by distinct IP value distributions. Moreover, the extending high IP distribution toward the deep is supposed to result from mineral dissemination, resulting in high resistive polarization anomalies and deeper conductive polarization anomalies caused by mineral enrichment. The above characteristics are considered the indicators of VMS minerals in such area.
To sum up, the IP-incorporated inversion facilitates the interpretation of TEM data collected over high polarization areas. However, the serious ill-pondness issue of multiparametric inversion brings a great challenge to result reliability, which largely depends on the selection of the starting model and inversion scheme. Integrating the geological and geophysical information in the inversion offers a promising way to avoid misinterpretation
How to cite: Lu, J., Wang, X., Guo, M., and Xue, S.: Application of the semi-airborne transient electromagnetic method over the VMS deposit and data interpretation incorporating induced polarization effects, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7917, https://doi.org/10.5194/egusphere-egu25-7917, 2025.
Geophysical techniques are an efficient method for identifying hidden hazards in embankment dams due to the presence of significant physical differences in dam hazards. However, there is still a lack of sufficient understanding of the coupling relationship between different geophysical fields of different hazards, which hinders the detection accuracy of geophysical methods. By combining the theories of seepage field, stable electric field, electromagnetic wave field, and elastic wave field, a multi-physics coupling equation and boundary conditions for the hidden hazard model of embankment dams are established. Based on different geophysical methods, the geophysical responses of dam models with different water levels, hazard types, and sizes were modeled and used as the library of training samples. These samples were thoroughly trained using the YOLO convolutional network model, and training metrics like recall, accuracy, and loss curve were used to assess the quality. The results indicate that the GPR and seismic images are more accurate in identifying the hazard of the cavity, ant nest, and fracture, whereas the ERT is more successful in identifying the leakage risks. In addition, the location of the submerged surface can be accurately determined by the ERT, which is more sensitive to the water level.
This work was funded by the Science and Technology Project of Jiangxi Province (2022SKLS04, 2023KSG01008) and the National Natural Science Foundation of China (42374097)
How to cite: Yu, H., Hu, S., He, S., Chen, H., Deng, J., and Wang, S.: 3-D modeling of coupled geophysical fields for hidden hazards in the embankment dam using YOLO convolutional network model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14126, https://doi.org/10.5194/egusphere-egu25-14126, 2025.
Thrust fault zones around the Tibetan Plateau (TP) record the tectonic evolution between the Plateau and its surrounding terranes, which is helpful for understanding the uplift mechanism and deformational processes of the TP. The Longmenshan fault (LMSF) is the tectonic boundary (TB) between the Yangtze terrane (YT) and Songpan-Garze terrane (SGT), while the TB of its western segment, either the Lijiang-Xiaojinhe fault (LXF) or Jinhe-Qinghe fault (JQF), is controversial. Therefore, we conducted magnetotelluric (MT) imaging, surface structure surveys, and petrologic analysis to further determine the deep–shallow structural relationship of the western LMSF segment. Resistors R1 and R2 revealed by MT imaging may have originated from different magmatism. Among them, R2 may have originated from plume underplating, which is consistent with previous studies, while R1 may have originated from the residue of episodic mafic magma intrusion along the JQF over a broader period. Based on regional geophysics, surface structural patterns and petrologic mineralogy, it is suggested that the JQF may have deformed deep into the lower crust or upper mantle, accommodating the southeast expansion of the TP by thrusting and acting as the TB between the YT and SGT before ~15 Ma. After ~15 Ma, due to the activation of the large-scale strike-slip faults, the LXF gradually replaced the JQF to dominate the structural deformation of the western LMSF segment. Our results indicate that the above tectonic transition might be associated with the geodynamic process from centralized deformation to diffuse deformation within the southeast TP during the late Cenozoic.
How to cite: Qiao, W., Jian, Y., Shibin, X., and Guozhong, L.: Cenozoic tectonic transition within the western segment of theLongmenshan fault, southeast margin of the Tibetan Plateau: Insights fromgeological and geophysical data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3388, https://doi.org/10.5194/egusphere-egu25-3388, 2025.
In the realm of railway infrastructure, the safety of railway road base structures is of paramount importance. A conventional railway raod base is composed of three distinct layers: square cement sleepers positioned at the top, ballast situated in the middle, and undisturbed bedrock or soil at the base. Railway roadbase are prone to a variety of structural challenges that can manifest differently based on their geographical context. In excavated railway sections, particularly those located in limestone regions, the occurrence of karst cracks and cave formations is a significant concern. Such geological phenomena may lead to the ballast stones falling into underlying cavities, thereby diminishing the thickness of the ballast layer. This reduction can adversely affect the bearing capacity of the railway sleepers, thereby compromising safety during train operations. Additionally, during the summer months, ballast may become saturated with rainwater, resulting in the formation of mud and mud overflow to the ground surface; conversely, in winter, the volume of ballast may increase due to ice heaving, leading to deformation of the railway track and square cement sleepers. Both scenarios pose safety risks for train operations and necessitate a thorough investigation of the ballast structure with ground penetrating radar.
To assess the condition of the raiway ballast structure, a Ground Penetrating Radar (GPR) system, along with three sets of air coupled antennas operating at a center frequency of 1.0 GHz, was employed. The antennas were strategically positioned at the front of the train, elevated 45 cm above the square cement sleepers, and arranged on the left, center, and right sides of the railway track. The GPR system successfully detected the railway cement sleepers and ballast structures, producing a two dimensional longitudinal profile for each antenna. The hyperbolic reflections generated by the cement sleepers were pronounced, which interfered with the emitted signals from the ballast, obscuring the ballast interface. Data processing was performed using a specialized local removal curve algorithm, which utilized a raw profile to subtract the local curve profile of the square cement sleepers, thereby eliminating the influence of the square cement sleepers. This data processing procedure resulted in a continuous reflection signal from the ballast layers, allowing for the identification of water distribution in water-bearing areas, variations in ballast thickness, and the structural characteristics of the railway subgrade and ballast layers in limestone regions. The Ground Penetrating Radar equipped with a horn antenna was utilized for scanning the railway ballast, yielding ballast clear reflection signals when combined with the specialized local removal curve method, thereby enhancing railway safety.
How to cite: Deng, X.: The method to get clear image for the railway ballast structure with the Ground Penetrating Radar Horn Antenna, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1404, https://doi.org/10.5194/egusphere-egu25-1404, 2025.
The definition of apparent resistivity is a critical aspect of in electromagnetic methods, particularly in the context of the electrical source transient electromagnetic method (ESTEM), which has not been well resolved. This study presents a novel concept termed pulse impedance for ESTEM, which is defined as the ratio of the first-order time derivative (pulse response) of the horizontal electric field to the vertical magnetic field. This innovative definition facilitates the derivation of a clear and explicit expression for apparent resistivity that maintains accuracy across the entire range of periods. The pulse impedance approach notably eliminates the source term from the calculations, resulting in an apparent resistivity that is independent of source parameters, thus enhancing the robustness and reliability of the resistivity estimations. The efficacy of this approach was corroborated through the analysis of data obtained from both numerical simulations and field measurements.
How to cite: Chen, W. and Zhu, Y.: Pulse Impedance: A New Approach to Defining Apparent Resistivity of Electrical Source Transient Electromagnetic Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1844, https://doi.org/10.5194/egusphere-egu25-1844, 2025.
Lithology identification is crucial in mineral and energy resource exploration as it determines geological composition and guides exploration activities, improving resource location and evaluation efficiency. The advancement of artificial intelligence technology has promoted the application of machine learning-based multi-source geophysical data fusion methods in lithology identification. However, due to the differences in geophysical exploration techniques and data types across mining areas, single machine learning methods often struggle to adapt to diverse geological environments, lacking necessary universality and robustness, which severely restricts the practical application of intelligent identification technology in actual exploration. To address these limitations, this study introduces a Multi-mode Adaptive Prediction System (MAPS) for lithology identification. MAPS innovatively integrates three learning models (supervised, semi-supervised, and unsupervised learning), and can automatically select the most suitable learning mode based on prior information such as the quantity and quality of existing labeled samples and the completeness of geological background information, achieving rapid and accurate lithology identification. We verified MAPS's performance advantages through extensive comparative experiments: in supervised learning mode, compared to Support Vector Machine (SVM) and Naive Bayes classifier, accuracy improved by 0.7% and 3.5% respectively, with F1 scores increasing by 3.4% and 4.5%; in semi-supervised learning mode, compared to semi-supervised fuzzy C-means algorithm and self-learning algorithm, accuracy and F1 scores improved by a minimum of 33.67% and 0.15 respectively; in unsupervised mode, compared to traditional fuzzy C-means and Gaussian mixture models, MAPS demonstrated superior ability to mine and construct internal data structures, showing stronger feature learning capabilities. Furthermore, MAPS has shown excellent performance in the practical application of coal seam location prediction. The coal seam locations predicted by the system are highly consistent with actual drilling results, further validating MAPS's significant application potential in practical engineering. In conclusion, MAPS significantly improves the efficiency and accuracy of lithology identification, providing reliable technical support for mineral and energy resource exploration with broad application prospects.
How to cite: Lv, P., Xue, G., and Chen, W.: Lithology identification method based on Multi-mode adaptive prediction system: Algorithms and Applications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1868, https://doi.org/10.5194/egusphere-egu25-1868, 2025.
The study and characterization of caves is a complex problem because not all underground cavities are accessible and therefore cannot be characterized by direct methods, such as topographical or geomatic methods. Therefore, geophysical surveys play a key role, as they can provide information on the size and shape of underground cavities from surface measurements.
In this work, two underground cavities characterized by different geological contexts and located in eastern Sicily (Italy) were studied: i) the “Micio Conti Lava tube”, a lava cave located in the municipality of San Gregorio di Catania and ii) the “Chiusazza Cave”, a complex karst cave located in the area of Syracuse. The two caves were investigated using both DC resistivity surveys and direct methods for 3D reconstruction (terrestrial laser scanner (TLS) and photogrammetry by unmanned aerial vehicle (UAV)).
In the “Micio Conti Lava tube”, N. 11 ERT (electrical resistivity tomography) profiles and N. 18 TLS stations were performed, while in the “Chiusazza cave”, N. 11 ERT profiles and N. 23 TLS stations were implemented.
In both cases, aerophotogrammetry was used to generate the 3D models of the epigeal environments. Geoelectrical surveys were performed using the dipole-dipole quadripolar configuration and a cluster analysis (K-means) was performed on the 3D resistivity models of both caves. This analysis revealed for each site two groups of clusters, highlighting areas with different resistivity values. A comparison between the resistivity models and the clusters showed a good overlap between the clusters identified in the central portion of the two models and the areas characterized by the highest resistivity values. This approach allowed the identification of isosurfaces for both areas that enclose the areas associated with the shape, position and size of the investigated cavities. In the "Micio Conti Lava Tube" area, the cavity is characterized by resistivity values higher than 17000 Ω-m while, in the Chiusazza cave area, the cavity is identified by resistivity values higher than 4000 Ω-m.
Comparing the results obtained by resistivity and 3D TLS models, an excellent correspondence can be observed for the "Micio Conti lava tube". Instead, for the "Chiusazza Cave", the models do not seem to fit perfectly in the central portion, probably due to the limited coverage of geoelectrical surveys in this area due to the prohibitive logistic conditions of the site.
This study confirms that DC resistivity methods are suitable for identifying and characterizing underground cavities in different geological contexts. Cluster analysis allowed to identify the isosurface value to be assigned as the boundary of the area of the studied cavities. The results of this study clearly show that by integrating geophysical and 3D survey techniques, it is possible to increase the mapping and understanding capabilities of these geological structures, even if they are inaccessible from the surface.
How to cite: Morreale, G., Grassi, S., Messina, D., Monforte, P., Giudice, G., Quattrocchi, G., and Imposa, S.: DC resistivity surveys compared to direct 3D surveys methods to characterize underground cavities in eastern Sicily (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8531, https://doi.org/10.5194/egusphere-egu25-8531, 2025.
In ocean-continent transition zones at rifted continental margins, distinguishing between crustal rocks, hydrated mantle rocks, and the boundary between continental and oceanic mantle is crucial. These materials exhibit distinct resistivity characteristics, making them identifiable through geophysical techniques. Marine Controlled-Source Electromagnetic (CSEM) surveys are particularly effective in mapping subsurface structures both onshore and offshore due to their sensitivity to conductivity contrasts.
Our study focuses on using multiple geophysical techniques to investigate crustal and mantle rocks at magma-poor rifted margins. We focus on the continent-ocean transition at the Goban Spur, located southwest of the UK. Here, previous seismic work suggested the presence of a broad zone of exhumed serpentinised mantle, in between continental crust confirmed by drilling and oceanic crust represented by the prominent linear seafloor spreading magnetic anomaly 34. We deployed 49 seafloor instruments on a c. 200 km transect spanning these three basement types, coincident with a pre-existing high-quality seismic reflection profile, to collect seismic, magnetotelluric (MT), and controlled-source electromagnetic data.
For navigation, the CSEM system integrated USBL positioning, CTD measurements, and an altimeter. The transmitter utilized a compact waveform with a fundamental frequency of 0.25 Hz, enhanced by maximizing the amplitude of the 3rd and 7th harmonics. The transmitter dipole moment was 30,000 A·m, powered by a current of 100 A.
For data analysis, the compact waveform was processed in short 4-second time windows. We do stack the 4-second FFT up to 60 seconds or longer. This approach retained essential information while enhancing the signal-to-noise ratio, enabling robust time-series analysis.
CSEM and MT methods have shown promise in resolving debates about lithospheric structure. While these techniques have previously imaged fluid-rich zones in subduction settings, this study is the first to apply them to continent-ocean transitions in rifted margins. We present results from preliminary analysis of both CSEM and MT datasets, focusing on lateral changes in resistivity at the seaward limit of continental crust.
How to cite: Li, Y., Ivey, K., Constable, S., Minshull, T., and Bayrakci, G.: An electromagnetic investigation of the continent-ocean transition southwest of the UK., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8667, https://doi.org/10.5194/egusphere-egu25-8667, 2025.
The rapid growth of the oil and gas industry, driven by the increasing demand for fossil fuels, has led to significant environmental challenges. Among these, hydrocarbon pollution around refineries has emerged as a critical issue that was largely overlooked until recent decades. Romania, a prominent player in the petroleum sector, continues to rely on substantial reserves for fuel production. However, the environmental consequences of refining and transporting petroleum products were historically ignored, leading to widespread soil and groundwater contamination.This study focuses on the Petromidia Navodari Refinery, one of Romania’s most important refineries, and investigates the extent and impact of underground hydrocarbon pollution. To achieve this, geophysical methods such as electrometry and Ground Penetrating Radar (GPR) were employed alongside soil drilling for sample analysis. The investigation covered several zones, each spanning 400 to 600 square meters, and extended over several kilometers surrounding the refinery. Measurements reached depths of up to four meters, encompassing the water table—a critical layer for environmental and public health.
Electrometric data revealed high resistivity values at depths of 0.5 to 3 meters, indicating the presence of hydrocarbons, which impede electrical conductivity. These findings align with the depth of the groundwater table, highlighting the risk of pollutant transport through underground water systems to populated areas. GPR surveys identified anomalies at depths of 1 to 2.5 meters, corresponding to zones affected by hydrocarbon infiltration. The integration of GPR and electrometric data with soil sample analyses confirmed hydrocarbon contamination in these layers.
Using these datasets, a detailed map was created to illustrate the spread of underground pollution, revealing both the affected area and the dynamic movement of contaminants. Additional mapping of groundwater flow patterns allowed for the estimation of the speed and direction of hydrocarbon migration, enabling predictions of the contamination’s future expansion.
This research underscores the significant environmental impact of petroleum processing and transport, particularly the contamination of soil and aquifers. Such pollution poses severe risks to public health, agriculture, and ecosystems. By identifying the affected zones and quantifying the extent of contamination, this study provides valuable insights for mitigation strategies.
The findings emphasize the urgent need for stricter environmental policies and remediation measures around refineries. These should include monitoring systems, improved waste management practices, and technologies for reducing hydrocarbon emissions into the environment. The integration of geophysical techniques such as electrometry and GPR proves to be an effective approach for assessing and managing underground pollution.
In conclusion, the study highlights the critical importance of addressing refinery-related pollution through comprehensive assessments and informed interventions. By providing a scientific basis for action, this research supports efforts to mitigate the environmental and public health impacts of the oil and gas industry.
How to cite: Dragos, A. G., Anghel, S., Iordache, G., Baraitareanu, B., and Dudu, A.-C.: Geophysical Studies of Electrometry and GPR for Mapping Underground Pollution Spread Around the Petromidia Navodari Refinery, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19846, https://doi.org/10.5194/egusphere-egu25-19846, 2025.
Post-mining can raise environmental issues, including water contamination in tailings storage facilities. Contaminated mine drainage can occur in these facilities when oxygen and water come into contact with tailings containing sulfides. In the past 20 years, various reclamation methods have proven to be effective in preventing potential contamination, such as the use of multi-layer cover systems. These engineered covers consist of successive layers with different hydrogeological properties to prevent water from reaching tailings. One way of assessing the effectiveness of these covers on the field is to monitor the flow of water within the cover over time, using time lapse electrical resistivity tomography (TL-ERT) in conjunction with hydrogeological instruments. This method allows to recover the spatio-temporal distribution of the soil electrical conductivity, and thus providing an image of the water flow in the near subsurface.
The objective of this project is to monitor water flow within a mine cover system which acts as a barrier to water infiltration into tailings using TL-ERT. This approach involves the use of numerical models, combined with field and laboratory data processing.
This study presents preliminary results from the two-weeks field campaign that was conducted in Fall 2024 at a tailing storage facility in Quebec where a multi-layer cover system is installed on a 7% slope. The cover configuration consists of four layers: 30 cm of silt, 20 cm of gravel, 30 cm of moisture-retaining silt, and 20 cm of gravel as a capillary break (from top to bottom). A 32 m-long ERT profile was installed along the slope of this cover with 64 electrodes and a spacing of 0.5 m. A 20 cm-high, 30 cm-wide and 2.75 m-long trench was excavated perpendicularly to the ERT profile, one-third along the profile. An infiltration test was performed, during which a total of 2000 L of a 1000 μS/cm saline tracer was injected into the trench over a period of 4 hours. TL-ERT monitoring consisted of acquiring a dataset of 65 ERT images using the Wenner configuration, every hour during the infiltration test, and every 6 hours thereafter for a week.
Preliminary results from field data inversion showed a spatio-temporal variation in resistivity associated with the start of the infiltration test. Near the trench, the inverted conductivity increased by a factor of two soon after the start of the injection, and a slightly conductive bulb appeared along the slope in the hours following the test. In addition, over the course of the two-week recording period, the surface of the cover became increasingly resistive, which can be associated to a significant drop in temperature between the beginning and end of the monitoring period (no rain was monitored during the monitoring period). The future steps of the processing will include a temperature correction to ensure that resistivity variations are only attributed to water inflow. Finally, thermo-hydrogeological modeling of the multilayer cover system during the infiltration test will allow to compare the geophysical results with modeled water dynamics.
How to cite: Bedoui, L., Dimech, A., Boulanger-Martel, V., Bussière, B., Sylvain, K., Impinna, T., and Plante, B.: Field study on the application of time-lapse electrical resistivity tomography to assess the performance of an inclined multi-layer cover system reducing water infiltration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14411, https://doi.org/10.5194/egusphere-egu25-14411, 2025.
