Gravity Data Research Articles

Power-Type Structural Self-Constrained Inversion Methods of Gravity and Magnetic Data

The inversion of gravity and magnetic data can obtain the density and magnetic structure of underground space, which provide important information for resource exploration and geological structure division. The most commonly used inversion method is smooth inversion in which the objective function is built with L2-norm, which has good stability, but it produces non-focused results that make subsequent interpretation difficult. The power-type structural self-constrained inversion (PTSS) method with L2-norm is proposed to improve the resolution of smooth inversion. A self-constraint term based on the power gradient of the results is introduced, which takes advantage of the structural feature that the power gradient can better focus on the model boundary to improve the resolution. For the joint inversion of gravity and magnetic data, the power-type mutual-constrained term between different physical structures and the self-constrained term can be simultaneously used to obtain higher-resolution results. The modeling tests demonstrated that the PTSS method can produce converged high-resolution results with good noise immunity in both the respective inversions and the joint inversion. Then, the PTSS joint inversion was applied to the airborne gravity and magnetic data of the iron ore district in Shandong, revealing the shape and location of the mineralized rock mass, which are crucial information for subsequent detailed exploration.

Joint interpretation and modeling of potential field data for mapping groundwater potential zones around Debrecen area, Eastern Hungary

The Debrecen area, as part of the Great Hungarian Plain (GHP), is associated with a multi-aquifer system that is overly exploited to fulfill the development plans. This research aims to jointly interpret and model gravity and magnetic data to map the subsurface geology and structures that govern groundwater occurrence. Various potential field techniques, including spectral analysis, anomaly derivatives, analytical signal, and Euler deconvolution were employed to map the distribution and depth of the buried geological structures. The combination of the potential field techniques enabled the construction of a detailed lineament map, providing valuable insights into the distribution of the subsurface structural features. It was indicated that the main structural trend is NW–SE and NE–SW, that coincides with the main structural trends in Hungary. Subsequently, a lineament density map is derived, indicating that the eastern, central, and northwestern parts of the area form the most promising zones for groundwater prospection. The joint inversion of gravity and magnetic data has further enhanced the understanding of subsurface geology. The depth to the basement rock varied between 1.18 and 2.2 km. The highest depth to the basement meets with thick sedimentary sequences bounded by normal faults forming graben and horst structures. Moreover, the distribution of these sediments is investigated using lithological logs indicating the thickness of the main hydrostratigraphic units in the Debrecen area. These units include Nagyalföld Aquifer, Algyő Aquitard, Endrőd Aquitard, and Miocene Badenian Aquifer units, which mainly consist of sand, silt, marl, and gravel. The recent study demonstrated the effectiveness of the joint interpretation in enhancing the knowledge of lithology and geological structures. However, a detailed geophysical survey is recommended to characterize the hydrostratigraphic units in the Debrecen area.

Gravity Field Numerical Analysis and Depth Structure of the South-Eastren Caucasus

In this paper, the gravity anomalies of the Bouguer of the Absheron, Shamakhi-Gobustan and Pricaspian-Guba oil- and gas-bearing regions are interpreted by the 3D prism method. According to this model, a part of the earth's crust covering the crystalline basement is considered as a set of many prisms located nearby. The depth of the surface of the crystalline basement is calculated taking into account the change in density at the bottom of the low velocity zones of the upper part of the earth's crust and the dependence of the density difference on depth according to a quadratic law.
 For interpretation of the gravity anomalies in the Absheron, Shamakhy-Gobustan and Pricaspian-Guba regions, a sedimentary basin viewed as, a number of prisms placed in juxtaposition. The decrease of density contrast in sedimentary basins approximated by, a quadratic function. The contour map is sampled at 1160 equispaced points with 5 km interval. The depths to the interface separating sedimentary were calculated using a generalized computer program GR3DSTR for 3-D inversion of gravity data either for a constant density contrast or for a variable density contrast with depth.
 From 3D gravity model of the sedimentary layer, it was found that the maximum depth is in the areas of Gyuzdek and Meraza (11 km), and the minimum is in the areas of Gonakkend, Gilazi, Garabulag, Dubrar (4 km).
 The depth of the sedimentary layer around the Agzibirchala well varies within 6 km. The correlation of the distribution of the thickness of the sedimentary layer on the site with the seismic section and well sections was determined.
 KEYWORDS – gravity anomaly, sedimentary basin, oil and gas fields.

Resolving basement crustal architecture and extensional tectonics using 3D inversion modelling of airborne gravity data in the Otway Basin region, Victoria

Seismic reflection surveys are effective for imaging the crustal architecture of sedimentary basins including the top-of-basement, which is an important interface for understanding rift tectonics, structural controls imposed on basin fill, and basin system prospectivity. However, seismic data can be less effective where the basin is thick, logistics limit acquisition, or where vintage seismic are noisy. 3D inversion modelling of airborne gravity gradiometry data can be an effective complement or alternative. This study provides a logical, stepwise approach that tackles this problem by focussing on separating superimposed geophysical anomalies. We use the Otway Basin in southeast Australia as a ‘laboratory’ to demonstrate a systematic approach for understanding basin and basement geometry, using airborne gravity data in conjunction with other geoscientific datasets. The forward response of a starting model, built using only existing seismic interpretations, was a poor fit to the observed gravity data because gravity provides the net response of all rocks down into the mantle. Therefore, in areas where geology in the deep crust is complex - like the Otway Basin – the entire crust must be modelled to account for gravity signatures caused by basement geological heterogeneity, before the smaller gravity variations attributable to the sedimentary basin fill can be discriminated. This process targets anomalies in the residual gravity, speculates on their likely causes, builds a geological structure into the model to explain them, and then considers the next unexplained miss-match in the residual. Forward modelling and inversion results suggest gravity anomalies are caused not only by geological diversity in the basement, but also by Moho shape. Accounting for the gravity response of these deeper structures not only improves understanding of basement structures, but also improves the recovered geometry of the top-of-basement interface. Specifically, inversion results suggest the Portland Trough in the southwestern region is significantly deeper than previously thought.

Geophysical Anomaly Indicators for Mapping Lead-Zinc (Pb-Zn) in its Metallogenic Province, Southern Benue Trough, Nigeria

One of the major challenges facing the mineral industry in Nigeria and Africa at large is insufficient geophysical information. The cost of geophysical equipment is rising geometrically. However, most of these countries have archives of geophysical data that are underutilized. Secondary (Magnetic, gravity and radiometric) data were collected, filtered and interpreted to generate anomaly indicators for exploring Lead-Zinc ores in southern Benue Trough province. Algorithms were tested using the existing mining sites to constrain the interpretation. It can be deduced that the high response of the magnetic analytic signal, residual gravity, and potassium in the western part of the area are mineralization indicators. Therefore, the magnetic analytic method was used to extract the probable depth to the top of the minerals in the area, which ranges from 47 to 113m and corresponds with the field measurements. The mineralization potential map of the area was developed. High mineralization dominated the western part of the area where the mining sites are concentrated. Therefore, the Pb-Zn ores are delineable using aeromagnetic, gravity, and radiometric datasets.

Potential of machine learning algorithms in groundwater level prediction using temporal gravity data

Prediction of groundwater levels with precision and dependability is crucial for effective water resource development and management. This study was carried out to establish the relationship between groundwater level (GWL) and temporal gravity variation through five nonlinear machine learning (ML) models: Polynomial Regression (PR), Random Forest, XG- Boost, K-Nearest Neighbourhood (KNN), and support vector machine - radial basic function (SVM-RBF). These models were employed to predict GWL at a specific well located at the Hydrology Department, IIT Roorkee, India. The models were trained and tested using a dataset that includes gravity, time, and relevant hydro-meteorological factors like precipitation (P), temperature (T), evaporation (E), relative humidity (RH), and wind speed (WS). The study is organized into three groups of model runs: the first group considers gravity as the sole input parameter, the second group includes both gravity and time, and the third incorporates all hydro-meteorological parameters. Comparative evaluation of the models was done using four different evaluation metrics, i.e., coefficient of determination (R2), Root Mean Squared Error (RMSE), Mean Absolute Error (MAE), and Nash-Sutcliffe Efficiency (NSE). Results highlight XG-Boost as the most efficient model for predicting groundwater levels, demonstrating exceptional performance, particularly when gravity and time are the input parameters, yielding a minimum MAE of 0.11 and a maximum R2 of 0.97.

Delineation of the boundaries of San Blas basin, Mexico, merging gravity, magnetic, and seismic data

The San Blas Basin (SBB) is located within what is referred to as the Mazatlán Basin, in the offshore west of Mexico. The SBB is positioned in the southern part of the Mazatlán Basin, within a region that remains poorly understood. Specifically, details about its shape and size are currently unknown, and only a few studies have provided some understanding of its limits. To ascertain the extent of the SBB and define its boundaries, we employed satellite-derived gravity and magnetic models, along with analyses linked to these fields. We established structural continuity through spectral analyses of gravimetric and magnetic data and the interpretation of various published seismic profiles in the near area. We also applied various filtering techniques, including the removal of regional trends and the regional Gaussian filter. Some anomalies of the potential fields are repeatedly reproduced in the different processed maps. These features allow for a comprehensive geophysical interpretation of the area under consideration, which leads to the proposal of the boundaries of the SBB. Additionally, 3D inversions of gravimetric and magnetic data were carried out in the study area. From these data, a more detailed response was observed in the 3D gravimetry than in the 3D magnetometry. In the former, it was possible to characterize a series of high-density and low-density bodies that were arranged in defined orientations, which were associated with the migration processes of Baja California from its position 30 Ma to its current position. A pattern of progressive evolution of the basin is given, from 30 Ma to the Present.

Studying the theoretical basis and advantages and disadvantages of Logistic methods of the total horizontal Gradient

Edge detection is one of the most important steps in interpretation of magnetic and gravity data. In magnetic and gravity maps, it is difficult to distinguish adjacent sources due to their field superposition. Many different techniques have been used to determine the edges of sources. These techniques are based on vertical or horizontal gradients of magnetic and gravity data or combinations of them, and the edges of the geological structures are determined by maximum, minimum, or zero values in the output maps. One of the most popular techniques is the total horizontal gradient which is based on horizontal gradients of magnetic and gravity data. The capability of the total horizontal gradient technique in mapping the boundaries of deep bodies is very limited when competing with large-amplitude shallow bodies. Some enhanced modifications of the total horizontal gradient technique have been introduced to improve the boundary estimation results. These techniques are based on logistic functions and derivatives of the total horizontal gradient. In this study, we aim to estimate the effectiveness of the logistic filters of the total horizontal gradient. To obtain optimum results, these filters were tested on synthetic gravity and magnetic data and real magnetic data from the Zhurihe region (China). The findings show that the logistic filters can provide more accurate and sharper boundaries without false source edges than the total horizontal gradient. These techniques can determine the edges of shallow and deep structures at the same time. These results demonstrate that the logistic filters are useful tools for the qualitative interpretation of potential field data.

A Seismic Tomography, Gravity, and Flexure Study of the Crust and Upper Mantle Structure Across the Hawaiian Ridge: 2. Ka'ena

AbstractThe Hawaiian Ridge, a classic intraplate volcanic chain in the Central Pacific Ocean, has long attracted researchers due to its origin, eruption patterns, and impact on lithospheric deformation. Thought to arise from pressure‐release melting within a mantle plume, its mass‐induced deformation of Earth's surface depends on load distribution and lithospheric properties, including elastic thickness (Te). To investigate these features, a marine geophysical campaign was carried out across the Hawaiian Ridge in 2018. Westward of the island of O'ahu, a seismic tomographic image, validated by gravity data, reveals a large mass of volcanic material emplaced on the oceanic crust, flanked by an apron of volcaniclastic material filling the moat created by plate flexure. The ridge adds ∼7 km of material to pre‐existing ∼6‐km‐thick oceanic crust. A high‐velocity and high‐density core resides within the volcanic edifice, draped by alternating lava flows and mass wasting material. Beneath the edifice, upper mantle velocities are slightly higher than that of the surrounding mantle, and there is no evidence of extensive magmatic underplating of the crust. There is ∼3.5 km of downward deflection of the sediment‐crust and crust‐mantle boundaries due to flexure in response to the volcanic load. At Ka'ena Ridge, the volcanic edifice's height and cross‐sectional area are no more than half as large as those determined at Hawai'i Island. Together, these studies confirm that volcanic loads to the west of Hawai'i are largely compensated by flexure. Comparisons to the Emperor Seamount Chain confirm the Hawaiian Ridge's relatively stronger lithospheric rigidity.

Geological setting of the Phu Khanh Basin based on updated geological-geophysical data

The Phu Khanh Basin is a Tertiary sedimentary basin located in deep a water area adjacent to the continental shelf of Central Vietnam, which has been begun to form since the Eocene(?)/Oligocene to the Quaternary. This area has previously only been briefly studied based on satellite magnetic, gravity data and some 2D multichannel seismic lines. In this article, the authors present the most recently interpreted and merged gravity data to update the research results on geological structure, tectonics and the history of geological evolution of the Phu Khanh Basin, which are considered significant contributions for hydrocarbon exploration campaigns in the future. Our new results show that mechanism of the the Phu Khanh Basin formation was started by a rifting process with most of it located in the central basin, controlled by four main fault systems, including the NW - NE system, the NE - SW system, sub-meridian system and less active is the sub-latitude system. The evolution of the basin has undergone through four main phases of different tectonic deformation, which are characterized by its typical geodynamic regimes and tectonic activities. These evolutionary phases can be briefly described as follows: (i) Paleocene peneplanation phase, (ii) The active rifting phase in Eocene/Oligocene-Early Miocene, (iii) The Middle Miocene thermal subsidence phase and finally (iv) The Late Miocene-Quaternary shelf building phase. However, the issue of determining the Eocene age at the bottom of the basin has so far remained unclear and elucidated by the lack of deep wells penetrating the deepest region of the basin.

Processing and re-interpretation of gravity bouguer map of a selected area in the W-NW of Iraq

Geophysical data interpretation is crucial in characterizing the subsurface structure. The Bouguer gravity map analysis of the W-NW region of Iraq serves as the basis for the current geophysical research. The Bouguer gravity data were processed using the Power Spectrum Analysis method. Four depth slices have been acquired after the PSA process, which are: 390 m, 1300 m, 3040 m, and 12600 m depth. The gravity anomaly depth maps show that shallow-depth anomalies are mainly related to the sedimentary cover layers and structures, while the gravity anomaly of the deeper depth slice of 12600 m is more presented to the basement rocks and mantle uplift. The 2D modeling technique was used for the quantitative interpretation of a selected Gravity profile along the study area. The model section of the gravity profile illustrated the relatively high density of subsurface basement rocks and/or upward mantle process which causes the effect of positive gravity values. Furthermore, several faults are indicated in the sedimentary sections by potential gravity methods such as several grabens, half grabens, and horst structures which are identified in Bouguer depth maps by relatively high and low gravity values, these structures were also affected by the basement rock uplift and/or Mantle upwards.

Deep Structure of Siletzia in the Puget Lowland: Imaging an Obducted Plateau and Accretionary Thrust Belt With Potential Fields

AbstractDetailed understanding of crustal components and tectonic history of forearcs is important due to their geological complexity and high seismic hazard. The principal component of the Cascadia forearc is Siletzia, a composite basaltic terrane of oceanic origin. Much is known about the lithology and age of the province. However, glacial sediments blanketing the Puget Lowland obscure its lateral extent and internal structure, hindering our ability to fully understand its tectonic history and its influence on modern deformation. In this study, we apply map‐view interpretation and two‐dimensional modeling of aeromagnetic and gravity data to the magnetically stratified Siletzia terrane revealing its internal structure and characterizing its eastern boundary. These analyses suggest the contact between Siletzia (Crescent Formation) and the Eocene accretionary prism trends northward under Lake Washington. North of Seattle, this boundary dips east where it crosses the Kingston arch, whereas south of Seattle the contact dips west where it crosses the Seattle uplift (SU). This westward dip is opposite the dip of the Eocene subduction interface, implying obduction of Siletzia upper crust at this southern location. Elongate pairs of high and low magnetic anomalies over the SU suggest imbrication of steeply‐dipping, deeply rooted slices of Crescent Formation within Siletzia. We hypothesize these features result from duplication of Crescent Formation in an accretionary fold‐thrust belt during the Eocene. The active Seattle fault divides this Eocene fold‐thrust belt into two zones with different structural trends and opposite frontal ramp dips, suggesting the Seattle fault may have originated as a tear fault during accretion.

3-D probability density imaging of Euler solutions using gravity data: a case study of Mount Milligan, Canada

Euler deconvolution is a widely used automatic or semi-automatic method for potential field data. However, it yields many spurious solutions that complicate interpretation and must be reduced, eliminated, recognized, or ignored during interpretation. This study proposes a post-processing algorithm that converts Euler solutions produced by tensor Euler deconvolution of gravity data with an unprescribed structural index into probability values (p values) using the B-spline series density estimation (BSS) method. The p values of the Euler solution set form a probability density distribution on the estimation grid. The BSS method relies on the fact that while spurious solutions are sparse and ubiquitous, Euler deconvolution yields many similar or duplicate solutions, which may tightly cluster near real sources. The p values of the Euler solution clusters form multi-layered isosurfaces that can be used to discriminate neighboring target sources because the p values of spurious solutions are vanishingly small, making it simple to remove their interference from the probability density distribution. In all synthetic cases, the geometric outlines of anomaly sources are estimated from probability density isosurfaces approximating synthetic model parameters. The BSS method was then applied to airborne gravity data from Mount Milligan, British Columbia, Canada. Subsequently, results from synthetic models and field data show that the proposed method can successfully localize meaningful geological targets.

Mapping of Landslide Potential in Payung, Batu City, Indonesia, Using Global Gravity Model Plus (GGMplus) Data as Landslide Mitigation

Several areas in Batu City, Indonesia, often experience landslides when entering the rainy season; landslides occur at several points, including the Payung area on Jalan Trunojoyo. This area connects several districts in East Java, such as Malang Regency, Kediri City, and Jombang Regency. If this area experiences a landslide, the access road will be closed, forcing road users to look for another route that is further away. This study aims to map areas potentially prone to landslides on the Payung tourism road in Batu City, Indonesia. Gravity anomaly measurements were carried out using gravity data from the GGMplus satellite with a distance between data points of 220 m. The processing results are then correlated with the landslide hazard map made by InaRISK BNPB. Based on the residual anomaly map, the measured values are between -13.4 to -5 mgal (low), -5 to 5 mgal (moderate), and 5 to 12 mgal (high). Where the low zone shows the area with the lowest density, the low-density zone has a large enough landslide potential. So, the Trunojoyo road in the Payung area, Batu City, is a landslide-prone zone with very low rock density. The results of this study are expected to provide recommendations for mitigating landslides to the local government.

Detection of Subsurface Density Structures of the Aristarchus Plateau by Gravity Inversion

AbstractThe Aristarchus plateau, located at the center of Oceanus Procellarum, exhibits one of the most complex volcanic features on the Moon. To understand the subsurface three‐dimensional density distribution under the Aristarchus plateau, we performed gravity inversion using high‐resolution gravity data obtained from the Gravity Recovery and Interior Laboratory mission. Our inversion results indicate the presence of a strong lateral density differentiation, with some positive and negative density anomalies possibly exhibiting a correlation with the volcanic features observed on the surface. A linear high‐density anomaly near the Cobra Head magma source and an elliptical high‐density anomaly both exactly match the surface basaltic exposures observable in the remote sensing data. We executed the density separation to extract low‐density anomalies of the whole plateau and removed most of the density artifacts. The low‐density anomalies display elevated terrain evidence of multiple “semi‐ring” structures, suggesting the location of buried remnants of crater rims. The Aristarchus crater has a central low‐density anomaly in the exact size and shape of the later‐formed impact crater. This anomaly is consistent with the high crater porosity produced by extensive impact‐generated fracturing and dilatant bulking, though the observed gravity and density anomalies are greater in magnitude than expected for this process. The remote sensing data expose high‐silica material in the crater rim, implying that the young crater excavated an underlying layer containing both plagioclase and Si‐rich materials, and indicating that the local uplift of feldspathic and/or silicic materials also contributes to the high amplitude of the low‐density anomaly in the Aristarchus crater.

Delineating geological structure utilizing integration of remote sensing and gravity data: a study from Halmahera, North Molucca, Indonesia

Halmahera Island is the result of the interaction between the Indo-Australian Plate, the Molucca Sea Plate, and the Philippine Plate, which gave rise to many active geological structures that are vulnerable to seismic activity around the island. The complexity of this geological structure makes Halmahera Island very interesting to study. This study aims to identify geological structures by integrating remote sensing and gravity satellite data. Surface lineament analysis using the remote sensing method was carried out based on Sentinel-1A imagery data. The gravity method uses GGMPlus satellite data to clarify the continuity of geological structures that cannot be clearly mapped on the surface. Lineament analysis on gravity data uses techniques such as fast sigmoid edge detection (FSED) and Euler deconvolution. The results of lineament interpretation based on integrating remote sensing and gravity satellite data show that the NE-SW structure controls the northern and northeastern arms of Halmahera.
 In contrast, the southern arm is dominated by the NW-SE structure. The Euler depth estimation shows that the Halmahera area contributes to having geological structures at various depths. Deep structures reach 4 km, while shallow structures are found at depths of up to 2 km. Earthquake hypocenter data strengthen the interpretation of this geological structure. This comprehensive study yields an excellent correlation between gravity and remote sensing techniques in describing the general structural framework of the area. The new finding is an NE-SW trending geological structure on the northern Halmahera arm, which may be caused by two different tectonics first, the subduction of the Molucca Sea Plate with the Halmahera Plate in the west. Second, the strike-slip movement is trending NE-SW, which cuts the northern and northeastern arms due to the rotational movement of the thrust fault with the Philippine Plate to the west.

High-Resolution Gravity Measurements on Board an Autonomous Underwater Vehicle: Data Reduction and Accuracy Assessment

Gravity on Earth is of great interest in geodesy, geophysics, and natural resource exploration. Ship-based gravimeters are a widely used instrument for the collection of surface gravity field data in marine regions. However, due to the considerable distance from the sea surface to the seafloor, the spatial resolution of surface gravity data collected from ships is often insufficient to image the detail of seafloor geological structures and to explore offshore natural minerals. Therefore, the development of a mobile underwater gravimetry system is necessary. The GraviMob gravimeter, developed for a moving underwater platform by Geo-Ocean (UMR 6538 CNRS-Ifremer-UBO-UBS), GeF (UR4630, Cnam) and MAPPEM Geophysics, has been tested over the last few years. In this study, we report on the high-resolution gravity measurements from the GraviMob system mounted on an Autonomous Underwater Vehicle, which can measure at depths of up to several kilometres. The dedicated GraviMob underwater gravity measurements were conducted in the Mediterranean Sea in March 2016, with a total of 26 underwater measurement profiles. All these measurement profiles were processed and validated. In a first step, the GraviMob gravity measurements were corrected for temperature based on a linear relationship between temperature and gravity differences. Through repeated profiles, we acquired GraviMob gravity measurements with an estimated error varying from 0.8 to 2.6 mGal with standard deviation after applying the proposed temperature correction. In a second step, the shipborne gravity data were downward continued to the measurement depth to validate the GraviMob measurements. Comparisons between the corrected GraviMob gravity anomalies and downward continued surface shipborne gravity data revealed a standard deviation varying from 0.8 to 3.2 mGal and a mean bias value varying from −0.6 to 0.6 mGal. These results highlight the great potential of the GraviMob system in measuring underwater gravity.

Crustal density structure investigation of the East China Sea and adjacent regions using wavenumber domain 3D density imaging method

The East China Sea, situated at the intersection of the Eurasian, Philippine Sea, and Pacific plates, is characterized by complex geology influenced by tectonic phenomena such as plate movements, volcanism, faults, and uplifts. Crustal density structure inversion provides a thorough understanding of the region's geological history as well as Earth's dynamical evolution, providing critical insights into seismic disaster mitigation, resource exploration, marine environmental protection, and maritime safety. The inversion process, on the other hand, presents challenges in data quality, quantity, model complexity, uncertainty, and computational resources. With the advancement of next-generation satellite gravity measurements and developing inversion techniques, the inversion of marine crustal density structures promises to be more precise and comprehensive. We explored the density distribution in the East China Sea and surrounding areas using an innovative wavenumber domain three-dimensional density imaging method along with high-precision global satellite gravity data. By overcoming data quality and computing resource constraints, wavenumber domain three-dimensional density imaging has transformed the discipline of marine geophysics, successfully delivering accurate density distributions in the study area. We were able to get a more precise and comprehensive characterization of the crustal density structure by combining high-precision satellite gravity data and cutting-edge imaging methods. Our investigation has unveiled previously unknown details about density distribution in the East China Sea and its environs. The East China Sea shelf displays smooth low-density perturbations at 18 km depth, whereas the trench–arc–basin region exhibits increasing density perturbations. Notably, the Okinawa Trough, which is surrounded by the Tokara Volcanic Ridge and the Ryukyu Trench, displays strong positive anomalies with a north–northeastern to northeastern orientation. In contrast, the Ryukyu Ridge and the Philippine Sea Basin exhibit smaller negative values and substantial northwestward positive density trends, respectively. These findings indicate diverse material distribution, which provides important insights into the area’s geological evolution and tectonic processes. This study adds new insights into density distribution in the East China Sea and adjacent regions, offering information on the geological complexity of the region. The research lays the groundwork for future research on crustal dynamics and enhances the field of marine geophysics and related disciplines.Graphical abstract

Formation of the Lawn Hill Impact Structure

The Ordovician-aged Lawn Hill Impact Structure is perhaps unique among documented craters, in that it is largely filled with slumped, allochthonous Cambrian carbonates partly fluidised by the impact shock. It is a complex geological feature, with a thin horizon of suevite beneath carbonate sheets. The bulk of the impact ejecta material was either deposited on top of the mobilised carbonates, and not preserved owing to erosion, or is present beneath the base of current drilling. The geometry of the crater in its final form has been modelled in three dimensions using gravity data and dipole–dipole-induced polarisation geophysics, with control from an extensive drill-hole library. Post-impact modification, including terrace formation and carbonate fill, has resulted in an asymmetric ring syncline, which extends to depths >600 m. In the data-rich area of the Century zinc–lead–silver deposit, on the southwest margin of the crater, both intact and remnants of the crater rim and impact ejecta blanket were preserved above the deposit. The Proterozoic ore deposit is located on a detached terrace, which slumped into the crater and was buried by allochthonous carbonates from the Georgina basin. The sequence of events can be shown to comprise: impact with crater formation and injection of carbonate dykes and inter-thrust wedges in the crater walls with concurrent suevite deposits inside and surge deposits outside the crater; this was rapidly followed by slumping of carbonate mega-blocks transported by a fluidised carbonate slurry into the crater, concomitant with collapse of Proterozoic terraces; finally, collapse of the central crater uplift generated imbricate slices of Cambrian carbonate among mainly Proterozoic rocks inside the ring syncline.

Modernization of the basic gravimetric control network Polish Geological Institute – implementing a modern international gravimetric system and relationship with the historical Potsdam system

Abstract The project of the gravimetric database reambulation from the collections of the Central Geological Archives set itself the goal of ending the era of gravimetric bases dualism and transferring both databases: gravimetric base and archival gravimetric semi-detailed measurements to the modern frame of gravity reference, consistent with ITGRS/F definitions and realizations. This will strengthen the interpretational potential of gravimetric data and will open the possibility of fully integrating Polish gravity data with international databases of this type, and will also allow for the performance of modern works in relation to the modern gravimetric control network, i.e., in relation to the highest possible precision of the reference definition of gravimetric measurements in the country. Whenever the article refers to the units in which the gravity vector is determined, milliGal [mGal] is used, and the relation to the SI system is as follows: 1mGal = 10–5ms–2 or microGal [µGal] where 1µGal = 10–8ms–2.