Geophysical Studies Research Articles

Evaluating the performance of various models for deriving orthometricheights using Global Navigation Satellite System (GNSS) data

Orthometric heights are vital for fields such as topographic mapping, construction, engineering, and geophysical studies. This study examines the performance of five Global Geopotential Models (GGMs) and Global Navigation Satellite System (GNSS) data in deriving orthometric heights to determine the optimum model. Data from 21 ground control points were collected using South GNSS receivers, processed for ellipsoidal height, and compared with geoid undulations from five GGMs (EGM 2008, EIGEN-6C4, GECO, SGG-UGM-2, and XGM 2019e) to determine the orthometric heights. The derived heights were validated against existing orthometric data. The geoid models showed a high correlation (0.999), with EGM 2008, GECO, SGG-UGM-2, and XGM 2019e displaying similar standard deviations (0.06-0.07 m). EIGEN-6C4, however, was an outlier, with a higher standard deviation (SD = 4.8750 m) and lower minimum value (Min = 2.467m). Root Mean Square Errors (RMSEs) ranged between 10.92 m and 11.27 m for all models. Statistical tests, including t-tests and ANOVA, showed no significant difference between most models at a 95% confidence level, though GECO and XGM 2019e had a small, statistically significant difference. XGM 2019e was identified as the most precise model, showing a near-perfect correlation with other models with the least standard deviation.

Full-parametric and joint inversion of multimode surface wave data for identifying glacial ice thickness and freezing extent in subglacial sediments via the hunger games search algorithm

Determining glacier ice thickness and the extent of freezing in subglacial sediments are crucial in glaciological studies. Noninvasive geophysical methods, such as multichannel analysis of surface waves, are typically used for these tasks. In this study, we introduce a novel metaheuristic called hunger games search (HGS), which simulates the hunger-driven instincts and behavioral decisions of animals for the full-parametric inversion of seismic surface waves. We apply HGS to determine layer thicknesses, densities, S-wave velocities, and primary wave velocities of different layers through the joint inversion of multimode Rayleigh wave dispersion curves (RWDCs). This marks the first study using HGS for the inversion of dispersion data. Sensitivity studies of model parameters prior to the inversion indicate the necessity of postinversion uncertainty evaluations to mitigate the effects of varying sensitivity levels. In addition, a parameter tuning study is carried out to maximize the performance of HGS. Compared with some swarm intelligence-based optimizers (particle swarm optimization, cuckoo search, gray wolf optimization, sparrow search optimization, and whale optimization algorithm), HGS outperforms in the inversion of synthetic multimode RWDCs with 10% uncertainties with respect to a simulated glacier structure. In real data applications, a data set acquired at Midtdalsbreen, an outlet of the Norwegian Hardangerjøkulen ice cap, is inverted using the tailored HGS metaheuristic. The results obtained are consistent with previous geophysical studies. Furthermore, our analysis reveals that the performance of HGS when dealing with real applications is not highly sensitive to the selection of layers within the range of five to eight. The accuracy of HGS is undoubtedly contaminated by a larger model space; however, additional depth information derived from colocated ground-penetrating radar data can be directly integrated into HGS to obtain satisfactory results again.

Novel age constraints on offshore islets around Taiwan with implications for the Northern Taiwan Volcanic Zone

Determining the exact age of volcanic activity in the Northern Taiwan Volcanic Zone (NTVZ) is essential for comprehending Taiwan's tectonic evolution. The timing and duration of the volcanic processes that formed the NTVZ remain uncertain despite the availability of geochronological, geochemical, and geophysical data. While extensive efforts have been directed towards investigating the age of the Tatun Volcanic Group, the primary feature of the NTVZ, many other aspects require further examination. This study concentrates on two offshore islets in the northern region of the NTVZ. We present new 40Ar/39Ar ages of 0.252 ± 0.018 Ma for a lava flow, representing an early stage of volcanic activity, and 0.118 ± 0.012 Ma for a dike, representing the latest stage of volcanic activity around Pengjia Islet. A sample collected from Mianhua Islet did not yield a reasonable age due to high uncertainty, likely attributable to young and low radiogenic argon. Field observations support the interpretation that volcanic activity on both islets is considerably younger than previously estimated. This study corroborates the hypothesis from geophysical studies that submarine NTVZ features to record a potentially active magmatic reservoir offshore of northern Taiwan. By refining our understanding of spatio-temporal patterns in volcanic activity, this study contributes to volcanic hazard assessment in Taiwan and surrounding areas.

A Comparative Geophysical Study of Major Basins in the Pranhita–Godavari Rift, India and Rio Grande Rift, USA

ABSTRACT In this study, we compare and contrast two major sub-basins in the Pranhita-Godavari rift in eastern India (Chintalapudi subbasin) and the Rio Grande rift in the western United States (Albuquerque basin) using bouguer gravity data analysis and integrated profile modeling constrained with seismic, drilling, and geological data. The Chintalapudi sub-basin formed during the break-up of Gondwana around 350 Ma, while the Albuquerque basin formed much later (30–35 Ma) in the interior of North America approximately synchronous with extension in the Basin and Range province. The Chintalapudi sub-basin is narrow and deep; and associated with a −60 mGal (low) gravity anomaly that is mostly due to Gondwana fluvial sediments of late Carboniferous (~350 Ma) to early Cretaceous age (~120 Ma). The negative gravity anomaly associated with the Albuquerque basin is −55 mGals (low) and the Cenozoic sediments were deposited on Mesozoic and Palaeozoic strata with Precambrian crystalline rocks being exposed along the basin flanks. This sub-basin is wide and shallow. Major faults which bound these basins were delineated by gravity modeling that integrated all of the available constraints, and the average depth to the basement at the basin centers calculated from gravity modeling is 4–5 km. However, for Chintalapudi sub-basin, if the residual gravity anamoly is considered, it may be reduced to about 3.5 km.

Geophysical studies to delineate the subsurface structures and the sedimentary basin in the Ain Dalla area, western desert Egypt

Geophysical studies to delineate the subsurface structures and the sedimentary basin in the Ain Dalla area, western desert Egypt

Integrated remote sensing and geophysical studies of the Silet-Tin Felki area: Insights into the Pan-African tectonics and magmatic evolution of the Hoggar Shield, Southern Algeria

Integrated remote sensing and geophysical studies of the Silet-Tin Felki area: Insights into the Pan-African tectonics and magmatic evolution of the Hoggar Shield, Southern Algeria

Geotechnical and geophysical investigations for infrastructure safety zones: a case study of the supporting ring road, Cairo, Egypt

This study aims to evaluate the suitability of subsurface layers for infrastructure development using geophysical and geotechnical studies. Six seismic refraction and six 2D geoelectic profiles were conducted in the study area to analyze the geotechnical characteristics of the subsoil in order to assess its suitability for construction projects. According to the geophysical investigation, there are two main geoelectric strata, each with a different lithology and thickness. The first layer has high resistivity values of more than 200 (Ωm) and its thickness is between 3.5 and 6.3 m. The second layer's resistivity ranges from 0.3 to 200 (Ωm). The findings indicate that the near-surface area of the study site is composed of two layers in addition to the surface layer, which consists of semi-consolidated wadi fill deposits of gravel, sand, and silt with rock fragments. The first layer comprises fractured limestone with clay intercalation, followed by a second layer of marly limestone, which transitions into marl and clay. Both compressional (P) and shear (S) waves were detected and analyzed. The shallow seismic refraction technique indicates that the velocity waves (Vp) in the first and second layers range from 133 to 770 and 790 to 3100 m/s respectively. Various engineering parameters for the second layer were determined, including elastic moduli (bulk modulus, Poisson’s ratio, rigidity modulus, and Young’s modulus), competence scales (stress ratio, concentration index, material index and density gradient), and bearing capacity (ultimate and allowable). The average Poisson ratio for the first and second layers is 0.235. The ultimate bearing capacity (Qu) of the first layer ranges from 379.1 to 1031.2 gm/cm2 and between 1040.8 and 1548.5 gm/cm2 of the second layer. Allowable bearing capacity (Qall) for the first layer is between 126.4 and 343.7 gm/cm2, and for the second layer, it is between 346.9 and 516.2 gm/cm2. According to the geotechnical investigation's findings, the range of liquid limit (LL) values is between 41.20 and 86.30%, the range of plastic limit (PL) values is between 18 and 35.25%, the range of plasticity index (PI) values is between 14.17 and 51.45%, and the range of free swelling values is between 60 and 170%. However, the study identified high-risk areas in the study area. These zones are located in the first and second layers represented by strongly swelling clay layers and strongly fractured limestone, which will have a major impact on the road and buildings. Therefore, this study recommends addressing these problems before any development to protect these areas from subsidence and collapse.

Tectonic structures of SW margin of Gondwana from gravity and magnetic anomalies of the Río de la Plata area and their correlation with the Beattie magnetic Anomaly in South Africa

The Río de la Plata cratonic area and the adjacent continental platform (South America) have been subject of geophysical and tectonic studies for several decades. However, there are still many uncertainties related with its structural configuration and tectonic evolution. To deepen the knowledge of the tectono-structural characteristics of the cratonic and surrounding areas, we carried out an analysis of magnetic and gravity anomalies, which is highly effective in accurately locating the boundaries of crustal/lithospheric domains/terrains and structures. Additionally, this tectonic characterization allows us to correlate South American geophysical features with their counterparts in southern South Africa (i.e., Beattie Magnetic Anomaly).In this study, different filters and techniques were employed to analyze magnetic and gravity anomalies. The gravity anomaly was obtained from global models, whereas the magnetic anomaly was compiled from diverse sources (aerial, terrestrial, and marine data). Particularly, the first vertical derivative, total horizontal derivative, analytic signal, tilt angle and upward continuations were calculated, and 3D Euler Deconvolution was applied.Our results confirm the existence, and accurately determine the location, of Río Negro and Colorado transfer zones, Sierra de la Ventana Shear Zone, and extensional structures in the Tandilia System area, here defined as Tandil Trough. Moreover, we propose that the Sierra de la Ventana Shear Zone was shifted northwards in the offshore sector of the study area through sinistral displacement along the Punta Mogotes Shear Zone. Considering the similar rheological contrasts exhibited by the South African margin, we suggest an analogous configuration in the case of the Cape Fold Belt. Additionally, based on our interpretations, and considering previous geophysical studies, we support the proposal that the Beattie Magnetic Anomaly in South Africa and the magnetic anomaly detected beneath the Claromecó Basin would be generated by comparable sources (i.e., Sierra de la Ventana Shear Zone).

The deep electrical structure characteristics and regional seismicity of the southeastern Jiali Fault Zone

Located in the southeastern Tibetan Plateau, the Jiali fault zone (JLF) is an important strike-slip fault system, which delineates the southern boundary of the south-eastward extrusion of the Tibetan Plateau. The JLF features long-recurrent seismicity and plays an important role in balancing the local stress field. However, previous geophysical studies have mostly focused on regional studies in the northwestern segment and the southeastern end of the JLF. Few geophysical studies have been conducted on the JLF segment in the Eastern Himalayan Syntaxis region. To better understand the deep structures of the JLF and to provide geophysical constraints for the regional seismicity, we propose a crustal-scale resistivity model derived from magnetotelluric profile data across the three branches (Xixingla, Puqu, and Parlung faults) of the southeastern segment of JLF. The three-dimensional electrical structure shows that the JLF is generally characterized by a series of northeast dipping features. Unlike Parlung and Puqu branches, which are currently relatively inactive, the Xixingla fault is imaged to dip steeply in the shallow part of the crust and gradually turninto a gentle dip angle in the deeper section, before ultimately converging with a low-resistivity layer in the mid-to-lower crust. As the recent seismicity shows a combination of thrusting and strike-slip mechanisms, the primary strike-slip tectonic background for the regional seismicity may be modified by the northeastward compression from the subducting Indian Plate. Combined with other geological and geophysical evidence, we suggest that the reverse thrust and strike-slip displacement of faults may jointly contribute to the combined dynamic mechanism for seismicity in this area, due to the intrusion of the Namcha Barwa metamorphic complex beneath the Lhasa terrane.

Forecasting the quality of fluid seals and reservoirs for the Upper Jurassic deposits in the southeastern part of the West Siberian oil and gas province

Background. Upper Jurassic natural reservoirs are the main deposits containing 65–75% of recoverable hydrocarbon reserves in the Tomsk Region. They are overlapped by the fluid seals of the Bazhenov–Georgievsk complex, the quality of which deteriorates in the easterly direction. Therefore, to predict new promising areas, it is necessary to determine the quality and thickness of the Upper Jurassic seals and natural reservoirs. Objective. The need to forecast the quality of the Upper Jurassic fluid seals and reservoirs of the “Yu group” in the southeastern part of the West Siberian oil and gas province (Tomsk Region). Materials and methods. The paper uses regional and local studies of different years, materials and methods for interpreting geophysical well studies and seismic data from 2D reflection and core studies, databases of geological and geophysical information, methods of mathematical modeling of sedimentary basins and an original methodological approach proposed by the authors. Results. The time of the beginning of the lithification of the Bazhenov–Georgievsk rocks of the Upper Jurassic–Early Cretaceous (Aptian–Albian) was determined, and a regional model of the Georgievsk horizon distribution was constructed. The porosity of the Upper Jurassic natural reservoirs and the thickness of the Bazhenov fluid seal at the selected fields were calculated. Conclusions. The assessment of the quality of fluid seals and natural reservoirs made it possible to determine more promising areas for geological exploration using the oil and gas exploration criterion determined on the basis of the analysis of the thickness of the Georgievsk horizon (Kontorovich criterion). The efficiency of the proposed method is described using the example of the Upper Jurassic oil and gas fields in the Tomsk Region (Western Siberia).

IMPROVING THE RELIABILITY OF THE THREE-DIMENSIONAL GEOLOGICAL BASIS OF COMPLEX DEVELOPMENT TARGETS

This article proposes a new method for identifying different groups of reservoirs when constructing a three-dimensional geological and hydrodynamic model of the target. Productive formations of the Bajocian and Bathonian stages of the Jurassic system of the Kalamkas field were selected as the object of study. This field is tectonically associated with the northern part of the North Buzachinsky arch, located at the northwestern end of the Turan plate. It was noted that these productive deposits have a complex geological structure, due in lithological terms to uneven alternation of sand-siltstone and clay rocks. In addition, four different reservoir classes are identified within each tier, which are characterized by their own permeability-porosity correlation relationships. As a result, for reliable construction of the filtration field, it is necessary to determine the distribution zones of each of the identified reservoir classes within the reservoir. This is due to the fact that due to the different filtration field, the development of reserves from each group of reservoirs will occur unevenly both in area and in section. In this regard, the integrated Flow Zone Indicator (FZI) was evaluated using the results of laboratory core studies. In order to obtain a continuous FZI parameter for wells without core sampling and laboratory analysis, the results of laboratory studies were compared with the results of well geophysical studies (well logging). As a result, analytical dependence of FZI and log data was obtained. Based on this analytical dependence, new three-dimensional models were constructed and zones of distribution of different groups of reservoirs were identified. To verify the obtained results, the synthetic FZI curve calculated from the obtained analytical relationship was compared with the FZI estimate based on the results of laboratory core studies. It is concluded that the synthetic FZI curve is consistent with the FZI estimate based on the results of laboratory core studies and, therefore, the proposed approach can be used when performing work related to 3D modeling.

New subsurface structural insights of Northeast Vietnam: Advanced implications from high-resolution magnetic data

Northeast Vietnam is covered by sedimentary rocks, and its subsurface structures can be determined by geophysical studies. However, the structural patterns in Northeast Vietnam have so far been poorly studied and there is a lack of addressing the complex geological features of this area. Outlining such geological features is commonly achieved by applying various edge detection methods to magnetic fields. In this research, we applied nine enhancement techniques to magnetic data of Northeast Vietnam to identify geological features in this area. The methods are tested on synthetic data before applying to RTP (reduction to pole) magnetic data that are obtained from the multiple stage RTP technique. Four semiautomated depth estimation methods are also used to obtain the depth of magnetic structures in Northeast Vietnam. The results indicate that the normalized total gradient and power transform of the tilt angle of the total horizontal gradient can produce geological features more clearly than others. The findings show that the study area is dominated by NE-SW and ENE-WSW trending lineaments, and most of magnetic sources are around 1–2.5 km deep in the area. The NE-SW and ENE-WSW trending structures are possibly related to the left-lateral motion along the Ailaoshan–Red River shear zone. Our findings also show that Northeast Vietnam may be considered as a southwestern continuation of the South China Block. Our results provide a better picture of the structural features of Northeast Vietnam and overcome the gap in understanding the tectonic and geological framework of this important area.

Seismic Microzonation and Geotechnical Modeling Studies Considering Local Site Effects for İnegöl Plain (Bursa‐Turkey)

AbstractLocal site effects play a vital role in determining the level of structural damage to the structures built on soil. Therefore, correctly determining the underground layer structure and its physical characteristics in the lateral and vertical directions is essential for the geotechnical model. More information and more accurate results will be obtained if the geotechnical model is evaluated multidisciplinary together with geophysical studies, not only based on drilling results. For this purpose, vertical electric sounding, seismic refraction, microtremor, and mechanical drilling techniques were applied within the scope of geotechnical studies in the İnegöl district of Bursa. The methods were evaluated together, and the geotechnical cross‐sections of the underground were interpreted. In addition, microzonation maps determined from Geophysical parameters were created in the study area. These maps, geotechnical cross‐sections, and microtremor data evaluation results predicted how the study area's buildings and soils would behave under dynamic forces such as earthquakes. As a result, the soils in the study area were mainly saturated with water and had weak strength. Existing or newly constructed engineering structures on such soils are predicted from microzonation maps that will damage both the soils and the buildings in a seven‐magnitude earthquake.

Geological and mining mapping approach by coupling geological and geophysical field data: application to the Central Domain of the Mbere division (Adamawa-Cameroon)

This study is based on the coupling of geological field data with geophysical studies in the geological mapping of the Central Domain of the Mbere Division (Adamawa-Cameroon). The first step was to calculate the residual grid associated with the geophysical data that will be used for the mapping of the basement. The second step before mapping consisted in calculating the analytical signal associated with the residual grid, used to interpret the geological formations under cover or in intrusion. Subsequently, a geological mapping approach based on the categorisation of geophysical signatures into ranges using the Encom Discover program was adopted. This approach is based on the analysis of the relief of geophysical anomalies. The process of categorisation which is done iteratively, takes into consideration in the same georeferenced space, the resolution of the input data, the variation of the field considered and the structural model previously interpreted. The result of the categorisation is then compared to the spatial distribution of outcrop data to build the geological model. The application of this approach to the Central Domain of the Mbere Division led to the production of a synthetic geological map at a scale of 1/75,000. The superposition of this map to the topographic model allows to observe a concordance between the Cretaceous basins represented by their edge faults and the topographic depression zones. The various mineral indicators (primary and secondary) collected during the fieldwork, combined with the geological model (1:75,000 scale) as well as the Cretaceous deposits and vein intrusion models were used to create the mineral indicators and targets map for this sector. All these models can thus be used to underpin mineral exploration projects in the study area.

Geoelectric heterogeneities of the Pre-Dobrudga Trough a zone of hydrocarbon manifestations

For the first time, a geological and geoelectrical interpretation of the three-dimensional model of the Earth’s crust and upper mantle was carried out for the Pre-Dobrudga Trough and adjacent areas. It was based on observations of the Earth’s low-frequency electromagnetic field conducted in 2009―2012 by the National Academy of Sciences of Ukraine. The material confidently indicates that hydrocarbon occurrences are confined to the detected anomalies of high electrical conductivity. These are characterized by subvertical channels (from the surface to 10 km deep) galvanically connected with sediments or sub-vertical contact zones of different resistivity observed not only in the Earth’s crust (10―40 km) but also at crust-mantle depths (40―60 km) and in the upper mantle (110―160 km).The channels may determine the flow of ultra-deep fluids. The geoelectric criteria included maximum thickness of the sedimentary stratum, subvertical rise of electrical conductivity anomalies from the crust-mantle depths or column to the entire thickness of the Earth’s crust, subvertical boundaries of heterogeneities (contacts of different resistivity) in the consolidated Earth’s crust and upper mantle,presence of a highly conductive asthenospheric layer. We identified a significant number of local areas that can be considered promising for hydrocarbon occurrence. The majority of them spatially coincided with the already well-known oil and gas fields ― Skhidnosaratske and Zhovtoyarske, with the explored oil and gas prospective areas (Izmailska, Kyslytska, Prymorska, Shyrokivska), and with those that correspond to the areas of special permits for industrial exploration. However, the newly discovered areas that meet most of the geoelectric criteria, but for which no no information on oil and gas content is publicly available, clearly require additional geological and geophysical studies. It has been shown that zones of high electrical conductivity caused by the presence of deep fluids should be considered as deep centers of hydrocarbon generation and ways of their migration to the upper horizons of the Earth’s crust.

Long‐term monitoring of water table and saltwater intrusion dynamics through time‐lapse transient electromagnetic

AbstractUnderstanding hydrogeological processes often requires continuous measurements, which in many cases are not cost‐efficient. Time‐lapse geophysical studies are invaluable for investigating dynamic subsurface processes. They offer several advantages over traditional borehole‐based monitoring methods, such as being cost‐efficient and non‐intrusive. However, to be effective as an early warning tool, these studies must provide real‐time information on the processes. This is often not feasible with traditional geophysical methods, which typically do not offer real‐time monitoring. In this study, we present a windowed inversion approach for time‐lapse transient electromagnetic (TEM) monitoring. The advantages of this approach include: (i) immediate and continuous results as each time‐step dataset is acquired; (ii) no limitations on the size of the monitoring period or dataset; and (iii) the use of model information from previous inversion results for robust and continuous outcomes. The results from a synthetic study are followed by two field case studies, demonstrating the advantages of the windowed inversion compared to the inversion of the full dataset. We monitored the water table dynamics of a shallow unconfined aquifer over 8 months and the saltwater intrusion in a confined aquifer over 10 months using a monitoring TEM (mTEM) system while collecting nearly continuous daily measurements. With the windowed approach, the water table dynamics was recovered with an accuracy of 10 cm, and the changes in salinity were tracked with results comparable to those of an EC data logger.

Tectonic reevaluation of West Cameroon domain: Insights from high-resolution gravity models and advanced edge detection methods

The West Cameroon region, characterized by a diverse geomorphology of highlands and plains resulting from tectonic processes across different geological ages, has been extensively explored for natural resources. Recognizing the significance of its tectonic and magmatic features associated with seismic and volcanic activity, this study focuses on geodynamic investigations of the Cameroon Volcanic Line (CVL). Despite previous efforts, detailed structural geophysical studies of the West Cameroon domain have proven inconclusive, prompting a comprehensive structural reinterpretation. Utilizing the high-resolution SGG-UGM-2 satellite gravity model and innovative processing techniques, including the horizontal gradient of a modified tilt (HGSTDR), the balanced horizontal gradient (BHG), the tilt of the horizontal gradient (TAHG), the improvised horizontal gradient tilt angle (impTAHG), and the Tilt Depth method, our research aims to enhance the interpretational quality of tectonic lineaments. By separating regional and residual anomalies in the Bouguer gravity map and applying a combination of filters to delineate geological units, the BHG filter emerges as a robust tool that highlights subsurface edges without generating false features. This approach unveils previously undetected NNW-SSE-oriented lineaments, confirming the presence of deep fractures and faults in Bafoussam, Nkongsamba, and along the Benue Trough, corroborated by newly discovered NNW-SSW trending lineaments. The study suggests that the region’s topography is overcompensated by deep mountain roots and compressive tectonism. Digitizing the BHG filter produces a structural map, revealing predominant NE trends in identified geological margins, including NNE-SSW, N-S, NW-SE, E-W, and NE-SW directions. Geological contacts between granite and high-grade gneiss are indicated by NNW-SSE and NNE-SSW trending lineaments along the Benue Trough. These results contribute significantly to the understanding of the tectonic setting of the West Cameroon Domain.

INSIGHTS INTO THE MOHO DEPTH VARIATIONS AND CRUSTAL CHARACTERISTICS IN THE GUELMA–CONSTANTINE BASIN, NORTHEASTERN ALGERIA: A SHORT-PERIOD SEISMIC-RECEIVER-FUNCTION PERSPECTIVE

Teleseismic receiver functions (RF) were extracted from data collected at eight short-period, three-component seismic recording stations over the Guelma–Constantine Basin, northeastern Algeria, to improve the understanding of crustal structure and geodynamic processes. The H-κ stacking method was used to determine the Moho depths and average vP/vS ratios at each station. Careful linear inversion of RF was performed to determine the most appropriate average shear-wave and P-wave velocity profiles at each site. Both methods have yielded highly congruent results, with Moho depths showing robust correlations with previous seismological and geophysical studies. The previously observed pattern of the increasing Moho depth from north to south in the Tell Atlas has been confirmed. Furthermore, the identified transitional nature of the Moho in the Constantine Basin is consistent with a recent study. In addition, we identify a low-velocity zone (LVZ) at approximately 20 km depth within the southern Guelma Basin, confirming previous results in the Constantine Basin and suggesting an eastward elongation of the LVZ, at least into the southern periphery of the Guelma Basin. Examination of data from the northern tip of the Hammam Debbagh–Roknia NW–SE fault, the western boundary of the Guelma pull-apart basin, revealed a shallow Moho depth (22 km), less than the basin average depth of 25 km. The LVZ observed in the lower crust (12 km) suggests the presence of partial melts, consistent with gravimetric and chemical analyses of hydrothermal sources in the area. The extensional tectonic activity along this boundary, coupled with the low-viscosity zone and low average vP/vS ratio, is potentially associated with delamination processes. The effectiveness of our approach underscores its potential as a viable alternative or complementary method for investigating variations in the Moho depth.

Hydrogeological Characteristics and Geophysical Study of Base Aquifers in the Island of Grande Comore: Implications for Water Resources and Saline Intrusion

Hydrogeological Characteristics and Geophysical Study of Base Aquifers in the Island of Grande Comore: Implications for Water Resources and Saline Intrusion

Giant landslide, hidden caldera structure, magnetic anomalies and tectonics in southern Tyrrhenian Sea (Italy)

Phlegraean Fields and Ischia Island are large, densely populated, active volcanic structures located in the Campanian Tyrrhenian margin between the onshore and offshore sectors. While the emerged landforms provide significant insights into a series of intense volcano-tectonic events of the last 60 ka, our understanding of the sub-marine portion of these volcanoes remains limited due to its inaccessibility to direct exploration. In the last decades, the use of magnetic methods has proven to be useful in volcanic context, given the presence of large magnetization contrasts, whereas the implementation of a high-resolution Digital Elevation Model (DEM) has allowed the integration of detailed morphological analyses into the geophysical studies. In this work, we present two new high-resolution airborne and shipborne magnetic surveys, carried out by the National Institute of Geophysics and Volcanology (INGV) in the marine sector of the Phlegraean Fields caldera (Pozzuoli Bay) and surrounding sea sectors. Moreover, the new datasets have been integrated with older marine surveys carried out by the National Research Council (CNR) to extend the resulting magnetic anomaly map embracing the whole Campanian offshore volcanic structures, excluding Ischia Island. As a result, we present here three new magnetic anomaly maps used for an integrated interpretation of magnetic, morphological, and tectonic features. The study results provide valuable insights into the relationship between volcanic, magmatic, and tectonic activity, which may be useful for further investigations. Among the most notable findings are: the identification of the magnetic signatures of regional faults, previously unknown caldera structures, and a massive rock avalanche. Consequently, our research provides a significant contribution to seabed exploration aimed at identifying potential hazard factors in the study area.