Gravity Anomalies Research Articles

Lithosphere density structure of southeastern South America sedimentary basins from the analysis of residual gravity anomalies

We conduct a gravity study of the lithosphere beneath three large sedimentary basins in southeastern South America: Paraná, Chaco-Paraná, and Pantanal. We compile a massive gravity database and estimate the free-air and Bouguer gravity anomalies, resulting in a novel complete Bouguer anomaly map for the study area. To discern the influence of crustal loads with known lithologies, including sediments, basalts, and topography variations of the Moho discontinuity, we calculate their gravity effects and subsequently remove them from the complete Bouguer anomaly, leading to the development of our residual Bouguer anomaly map. This map highlights unknown anomalous masses within the lithosphere. To aid in the interpretation of these residual anomalies, we perform a 2D forward modeling. Based on our results, we propose new boundaries for the Paranapanema block and the Luiz Alves craton. Additionally, we propose that the Ponta Grossa swarm dike has a more substantial impact on the crust and lithosphere than previously considered, and delimit the region of influence of this magmatism in the lithosphere. Moreover, tectonic features such as the São Francisco paleocontinent and the Rio de La Plata craton appear to be associated with negative residual Bouguer anomaly regions. Furthermore, we identify and emphasize the significance of the Western Paraná Suture, which acts as a demarcation between the Paraná Basin region and the Pantanal and Chaco-Paraná basins. Remarkably, this suture appears to play a more important role in shaping the density structure of the southwest of South America than the age and tectonic history of the sedimentary basins.

Identifying Multi-Scale Gravity and Magnetic Anomalies Using Statistical Empirical Mode Decomposition: A Case Study from the Eastern Tianshan Orogenic Belt

Identifying multi-scale anomalies that have simple forms and geological significance is critical for enhancing the interpretability of gravity and magnetic survey data. In recent years, empirical mode decomposition (EMD), which was developed as a significant data-driven approach for analyzing complex signals, has been widely used in identifying gravity and magnetic anomalies due to its advantages of adaptability to nonlinear and nonstationary data. Nevertheless, the traditional EMD method is usually sensitive to outliers and irregularly spaced data because of the interpolation process in the construction of envelopes. In this regard, an extended algorithm called statistical EMD (SEMD) has been proposed based on the smoothing technique. In this study, for validation purposes, the novel SEMD method has been employed to identify multi-scale gravity and magnetic anomalies. The sensitivities of local polynomial and cubic spline smoothing methods in SEMD to combination and arrangement patterns of field sources including the size, depth, and distance in gravity and magnetic anomaly identification were investigated and compared by forward modeling under the same conditions. The results demonstrated that the local polynomial smoothing method performed better than the cubic spline smoothing method. Thus, in the case study, the SEMD method using the local polynomial smoothing technique was employed for identifying multi-scale gravity and magnetic anomalies in the eastern Tianshan orogenic belt, northwestern China. It has illustrated that the SEMD method provides a novel and useful data-driven method for extracting gravity and magnetic anomalies.

Parallel Multiple Methods with Adaptative Decision Making for Gravity-Aided Navigation

Gravity-aided navigation is an effective navigation method for underwater vehicles. However, the distribution of the gravity field may affect the measurement errors of gravity anomalies and the precision of gravity-aided navigation. In this paper, the upper and lower thresholds of the gravity field standard deviation are computed by the statistical properties of the local gravity field to classify each grid in the gravity map into different levels. A parallel multiple methods with adaptive decision making (PMMADM) for gravity-aided navigation is proposed which incorporates the gravity anomaly measurements, particle filtering, and maximum correlation method into the observation equation of the extended Kalman filter. The algorithm autonomously selects the observation variables in the filter by combining the gravity field standard deviation at the current position of the carrier with a decision tree. This approach can combine the characteristics of different gravity matching algorithms, reduce the impact of random noise in the measurements, and improve the positioning accuracy of gravity-aided navigation. Physical simulation experiments demonstrated that the proposed gravity matching algorithm achieves the high navigation accuracy and long-term stability in different gravity fields, and the mean value of positioning error is 620.72 m.

Steep subduction of the Indian continental mantle lithosphere beneath the eastern Himalaya revealed by gravity anomalies

Steep subduction of the Indian continental mantle lithosphere beneath the eastern Himalaya revealed by gravity anomalies

Influence of the asthenosphere on earth dynamics and evolution

The existence of a thin, weak asthenospheric layer beneath Earth’s lithospheric plates is consistent with existing geological and geophysical constraints, including Pleistocene glacio-isostatic adjustment, modeling of gravity anomalies, studies of seismic anisotropy, and post-seismic rebound. Mantle convection models suggest that a pronounced weak zone beneath the upper thermal boundary layer (lithosphere) may be essential to the plate tectonic style of convection found on Earth. The asthenosphere is likely related to partial melting and the presence of water in the sub-lithospheric mantle, further implying that the long-term evolution of the Earth may be controlled by thermal regulation and volatile recycling that maintain a geotherm that approaches the wet mantle solidus at asthenospheric depths.

Landslide susceptibility mapping of Penang Island, Malaysia, using remote sensing and multi-geophysical methods

Malaysia is one of the countries in the world experiencing landslides yearly due to natural events and human activities. Penang Island is Malaysia’s second most developed state and the largest by population. It is prone to landslides with devastating environmental impacts. Hence, the need to characterize its near-surface soil-rock conditions. This study uses remotely sensed data via frequency ratio (FR) techniques to identify landslide-prone areas based on different categories of landslide causative factors. To further understand the conditions and hydrodynamics of the soil-rock profiles causing landslides, electrical resistivity tomography and seismic refraction tomography were carried out at a landslide-suspected section in the study area. Also, the satellite-derived Bouguer gravity anomaly modeling was performed to map the varied gravity anomalies associated with landslide-triggering factors in lithologic units. The multi-geophysical models offer strongly correlated results with the causative remote sensed maps and the landslide susceptibility index (LSI) map. The likelihood of landslides occurring in the area, as suggested by the area under curve modeling of LSI data, yielded a high predicted success rate of 83.47%. Hence, prospective landslides were identified at the hilly and elevated sections, while the less susceptible sections were identified on flat reliefs. Landslides may also be triggered, for instance, at steep sections with varied contractive soil bodies and shallow structures. Most importantly, leveraging the LSI map would help the necessary agencies to forestall and mitigate future landslide occurrences in the area.

Seafloor and Ocean Crust Structure of the Kerguelen Plateau from Marine Geophysical and Satellite Altimetry Datasets

The volcanic Kerguelen Islands are formed on one of the world’s largest submarine plateaus. Located in the remote segment of the southern Indian Ocean close to Antarctica, the Kerguelen Plateau is notable for a complex tectonic origin and geologic formation related to the Cretaceous history of the continents. This is reflected in the varying age of the oceanic crust adjacent to the plateau and the highly heterogeneous bathymetry of the Kerguelen Plateau, with seafloor structure differing for the southern and northern segments. Remote sensing data derived from marine gravity and satellite radar altimetry surveys serve as an important source of information for mapping complex seafloor features. This study incorporates geospatial information from NOAA, EMAG2, WDMAM, ETOPO1, and EGM96 datasets to refine the extent and distribution of the extracted seafloor features. The cartographic joint analysis of topography, magnetic anomalies, tectonic and gravity grids is based on the integrated mapping performed using the Generic Mapping Tools (GMT) programming suite. Mapping of the submerged features (Broken Ridge, Crozet Islands, seafloor fabric, orientation, and frequency of magnetic anomalies) enables analysis of their correspondence with free-air gravity and magnetic anomalies, geodynamic setting, and seabed structure in the southwest Indian Ocean. The results show that integrating the datasets using advanced cartographic scripting language improves identification and visualization of the seabed objects. The results include 11 new maps of the region covering the Kerguelen Plateau and southwest Indian Ocean. This study contributes to increasing the knowledge of the seafloor structure in the French Southern and Antarctic Lands.

Evaluation of the precision of some new global Earth Gravitational Models in the East Vietnam Sea

This study is to evaluate the precision of some new global Earth Gravitational Models in the East Vietnam Sea, selecting the best model. The method and the program for calculating Free air gravity anomaly from the global earth gravitational model have been researched and developed. Evaluation of the precision of the models is done by comparing the models with ship-derived gravity anomalies. Data with anomalous signs are detected and removed when the deviation exceeds three times the root mean square deviation. The six global earth gravitational models were evaluated in the experimental section: EGM2008, EIGEN6-C4, GECO, SGG-UGM-1, XGM2019E, and SGG-UGM-2. The evaluation results show that: in the East Vietnam Sea, when compared with 35855 points of shipborne data, the above models respectively have standard deviations of: ±6.046 mGal, ±7.559 mGal, ±5.781 mGal, ±5.832 mGal, ±5.448 mGal, and ±5.236 mGal; all models have mean deviations from shipborne gravity anomalies of about +5 mGal; The correlation between the models and the shipborne data is quite good; The model SGG-UGM-2 has the highest precision. The Free air gravity anomalies from this model have also been calculated over the territorial waters of Vietnam in the form of a grid with a mesh size of 1' × 1'.

Tectonics and gravity field structure of Central Kazakhstan

Purpose. Identification of the nature of the manifestation of tectonic elements of different ages in Central Kazakhstan in gravitational fields based on the results of the calculation of regional, intra-crustal and local transformants. Methodology. Synthesis and analysis of the data on integrated interpretation and modeling of gravitational, geomagnetic, geothermal fields, the latest movements of the Earth’s crust and parameters of the seismic regime, tectonics and stratigraphy of rocks. Findings. Regional, intra-crustal and local heterogeneities in the lithosphere manifest themselves differently in blocks of Precambrian rocks, Early and Late Caledonides, Early and Late Hercynides. They may be associated with the processes of Paleozoic intracontinental rifting, with the rise of mantle matter and its emplacement into the Earth’s crust, followed by the manifestation of Late Paleozoic orogenesis, doubling of the thickness of the Earth’s crust, outpourings of magmatic formations. Originality. It is established that large gravitational minima are distinguished in areas with Hercynian folding, characterized by abnormally high amplitudes in the movement of the Earth’s crust. In the regions of the Caledonian folding, the values of gravity field anomalies of intermediate intensity and increased amplitudes of the latest movements of the Earth’s crust are manifested. Areas with Pre-Paleozoic folding have relative maxima of gravitational anomalies and minimum values of the latest movements of the Earth’s crust. Earthquake sources are concentrated in the consolidated crust at the junction of areas with different ages of basement consolidation, in gradient zones of geothermal, geomagnetic and gravitational anomalies. According to the variations of the intra-crustal transformant, it was found that a wide range of changes in the values of the gravitational field corresponds to areas with minimal temperature values, whereas in areas with increased temperature values, the range of changes in the values of gravity anomalies is reduced. The distribution of the local transformant of the gravitational field indicates the existence of highly variable anomalies, which reflects the high-frequency gravitational effect of near-surface objects of the Earth’s crust. Practical value. The distribution of inhomogeneities in the lithosphere with various density, geomagnetic and geothermal anomalies of geophysical fields, the nature of the seismic regime and the latest movements of the Earth’s crust predetermined the formation of geostructures with different types of mineralization, each of which is recommended to be searched and explored by a specific rational set of geophysical methods.

Influence of Lateral Plume Channel on the Evolution of Rift Arms of the Afar Triple Junction: Constraints From 3‐D Gravity Interpretation

AbstractThe Afar region presents a unique example of a juvenile R‐R‐R triple junction with the arms evolved to various stages of maturity. The lithosphere in this area has been modified heterogeneously by the nearby Afar mantle plume. To gain a comprehensive and consistent understanding of the link between crustal geometry and geodynamics of the region and facilitate comparisons across different tectonic elements, we developed a high‐resolution crustal thickness map of the region that resolves major tectonic features. The calculation involved a well‐constrained 3‐D inversion of upper mantle‐corrected crustal Bouguer gravity anomalies computed with the help of tomography‐derived densities. Our results match earlier localized crustal thickness estimates, illustrating the method's efficacy. A thinner crust (∼20–26 km) is revealed in the Afar compared to adjacent continental regions. The Main Ethiopian Rift has the thickest crust in the central part of the rift (∼38–40 km) and thinner to the north (∼30 km) and south (∼35 km). The crustal thickness along the Gulf of Aden changes from east (∼5 km) to west (∼17 km) in the west, consistent with a westward transition from seafloor spreading to continental rifting. The southern Red Sea is characterized by asymmetric crustal thickness, with a thicker crust (∼17 km) on the eastern flank compared to the western flank (∼11 km), which we attribute to the influence of a sub‐lithospheric channel from the Afar mantle plume. We propose a model describing the channel leading to asymmetric features of the southern Red Sea, such as crustal accretion, marginal topography, and volcanism.

Caldera-Like Delineation and Geological Resources Identification of Majenang Area, Indonesia by Gravity and Magnetic Data Inversions

Indonesia’s archipelago formed by the tectonic evolution proceeded with subduction, which was accompanied by volcanism. The systematic subduction zones produce the magmatic arcs with different periods since the Permian up to the Tertiary. However, only the recent Quaternary volcanic arc is recognized and lacked of information about the ancient volcanic environment. Calderas are a crucial feature in any volcanic environment due to the prospect site of geological resources. The Gravity and Magnetic methods are commonly used for preliminary study in almost any cases due to their light-weight, low-cost, and ability to map a wide area rapidly. The inverse-modeling scheme was invoked to estimate the sub-surface situation during the interpretation processes. The study intended to show the ability of both gravity and magnetic method for delineating of caldera-like environment including geological resources prospective site identification. According to the research, a northwest-southeast dextral strike-slip fault found in the area and belongs to the Pamanukan-Cilacap Fault Zone (PCFZ). A circular caldera-like anomaly delineated and interpreted as the ring fault of an ancient volcanic caldera in the study area. Several high gravity anomalies found within the caldera rims are interpreted as lava domes or intrusion rocks, while the high-density found following the outer part of the ring-fault terrain is interpreted as the buried lava. The ancient eruption point inferred around Majenang city, thus the study area proposed as the Majenang Caldera. A mineralization zone identified around the study area, which is comparable with the Cihonje people’s gold mining site as the proven prospective area.

Gravity aspects for Mars

We use the recent global gravity field model of Mars (Konopliv et al., 2020) and compute the gravity aspects (descriptors). We introduce a unique method working with the gravity aspects for Mars to achieve novel information about Mars for geologists, geophysicists and others than is feasible by using traditional gravity anomalies alone. New map of gravity aspects allows a better constraining of possible northern paleo-ocean using the MOLA topography, the combed gravity strike angles and features of the fretted terrain as constraints for a “mean” paleo-seashore. The Valles Marineris would contain water that would flow into this ocean.

Continental and island arc segmentation: Implications for retro‐arc and pro‐arc foreland basin and backarc basin geometries and sediment distributions

AbstractSegmented magmatic arcs create arc‐parallel variable loads and influence associated foreland basins through flexural isostasy along strike, in addition to standard subduction‐perpendicular foredeep/forebulge/backbulge models. Segmentation occurs in both continental and island arcs (Aleutians, Calabria, Japan, Kuril/Kamchatka, Lesser Antilles, Solomon Islands and Sumatra/Java). Some segments have variable gravity anomalies and elastic thicknesses (Te). In standard theory, the load created by an orogenic belt/magmatic arc depresses the lithosphere modelled as a thin elastic plate floating on a fluid mantle substrate, leading to an arc‐perpendicular foredeep, forebulge and backbulge. Arc‐parallel topographic and gravitational features should influence loading along strike in a similar way, resulting in a checkerboard pattern of foredeeps, forebulges and backbulges in both pro‐arc and retro‐arc foreland basins. This pattern exercises profound controls on sediment and facies distribution in a here‐to‐fore un‐envisaged manner, with implications for resource exploration in foreland basins.

Local gravity and magnetic anomalies associated with the oil and gas reservoirs in the cretaceous carbonate deposits of Yevlakh-Agjabedi depression, Azerbaijan

Local gravity and magnetic anomalies associated with the oil and gas reservoirs in the cretaceous carbonate deposits of Yevlakh-Agjabedi depression, Azerbaijan

2D modelling the depth of the southeastern Thrace Basin by using Bouguer gravity anomalies

2D modelling the depth of the southeastern Thrace Basin by using Bouguer gravity anomalies

Crustal structure beneath and surrounding the Appalachian Basin region of Eastern North America imaged by joint inversion of P wave receiver functions and surface wave dispersion measurements

SUMMARY To evaluate the plate flexure model for the formation of the Appalachian Basin, we investigate the extent to which crustal structure beneath and surrounding the basin was modified by the Palaeozoic orogenic events that created the basin. We jointly invert receiver functions and surface wave dispersion measurements to obtain 1-D crustal Vs profiles for 261 seismic stations located within and around the basin. The average crustal thickness for the region is 44 km, and the crust gradually thins to the east, consistent with previous studies. Four areas of anomalous crust are identified with respect to the eastward thinning of the crust. An area of thick crust is found along the Grenville Front on the western side of the Appalachian Basin where the crust thickens by ∼5–10 km. Moho depths of up to 54 km in this region likely result from suture-thickening. The crust is thinner beneath the Neoproterozoic Scranton rift by ∼5–7 km, coincident with a ∼40 mGal Bouguer gravity high. Across the Neoproterozoic Rome Trough, the crust thins by ∼4–5 km, coincident with a ∼10 mGal Bouguer gravity high. Density models for these rifts show that the rift-related crustal thinning is sufficient to explain the gravity anomalies. The Vs models obtained for stations in the rifts indicate little, if any, mafic layering in the mid-crust and only a modest amount of mafic layering in the lower crust. In the northwestern portion of the Appalachian Basin in northeastern Ohio and northwestern Pennsylvania within the Elzevir block, another area of anomalously thick crust (50–52 km) is found. This region is not associated with any known tectonic structures or boundaries or a gravity anomaly. The lower ∼5–10 km of the crust in this region is characterized by high (>3.9 km s−1) shear wave velocities and thus appears to be mafic. The origin of anomalous crustal structure in all four areas is best attributed to Precambrian tectonic events that predate the formation of the Appalachian Basin, indicating that the crystalline crust beneath and surrounding the basin was not significantly affected by the Palaeozoic basin-forming orogenic events, a finding which supports the use of plate flexure models for understanding basin formation.

Analysis of a Relative Offset between the North American and the Global Vertical Datum in Gravity Potential Space

The accurate estimation of the zero-height geopotential level in a local vertical datum (LVD) is critical for linking traditional height reference systems to a global height system. In this paper, we investigate the theoretical and practical challenges involved in determining the offset between the North American vertical datum (NAVD) and the global vertical datum (GVD). Drawing on the classical theory of the vertical system in physical geodesy, we define the vertical datum offset and derive rigorous formulas for its calculation. We examine various factors that affect the determination of the offset, including the global gravitational models (GGMs), geodetic reference system, tide system, tilt error, and omission error. Using terrestrial gravity data and gravity anomalies from multiple GGMs in conjunction with Global Navigation Satellite System (GNSS) and orthometric heights, we estimate the vertical offset between the NAVD and GVD. Our results indicate that the geopotential difference approach and the geodetic boundary value problem (GBVP) approach yield consistent results. When the normal gravity geopotential of the geodetic reference system is selected as the gravity geopotential of the global height datum, the NAVD is approximately 0.04 m higher than the GVD relative to the GRS80 ellipsoid, and 0.97 cm higher than the GVD relative to the WGS84 ellipsoid. When the Gauss–Listing geopotential value is chosen as the gravity geopotential of the global height datum, the NAVD is roughly 1.45 m higher than the GVD relative to the GRS80 ellipsoid, and approximately 0.52 m higher than the GVD relative to the WGS84 ellipsoid.

Unravelling a midcrustal seismogenic fault structure from a seismic sequence and geophysical data: application to the 28 October 2022ML 4.1 Goesan earthquake in the central Korean Peninsula

SUMMARYEarthquakes in the Korean Peninsula often occur in subsurface hidden faults that are hardly identified before the seismic activity. We investigate a midcrustal subsurface hidden fault in a seismically quiescent region of the central Korean Peninsula that produced the 28 October 2022 ML 4.1 earthquake. A combined analysis of seismicity, geophysical properties and geological features constrain the subsurface fault geometry. The midcrustal fault may extend to the lineament on the surface that presents low gravity anomalies. The focal mechanism solutions and seismicity distribution suggest that the lineament may correspond to the surface trace of the fault. Further, the responsible fault is a left-lateral strike-slip fault with dip of 88° and bilateral rupture at depths of ∼12–14 km. The lateral extent of the fault may reach >25 km. A series of foreshocks formed the source zone to induce the main shock. The main shock nucleated at a location of lateral contrasts of heat fluxes and magnetic anomalies in the fault. The strong ground motions by the main shock are amplified by the sedimentary layers in the event site, inducing aftershocks to spread along the fault with time. The fault orientation is laid to respond to the ambient stress field. The Coulomb stress changes induced by the main shock load stress the fault, increasing the possibility of another earthquake occurrence. The study suggests that a combined analysis of seismicity, geophysical properties and geological features may provide constraints on seismogenic subsurface hidden faults.

Correlations between the Topography-Induced Gravity, Terrain Structure and the Seismicity in the Gulf of Panama

This study presents new maps of the topographic and geophysical setting and seismicity in the region of the Gulf of Panama. The spatial analysis is based on the comparative analysis of the datasets on geoid, free-air gravity anomaly, topography and earthquakes. The cartographic framework is developed using the Generic Mapping Tools (GMT) scripting toolset. Seismic activity in the Central America is high due to the complex geologic setting, tectonic activity and lithosphere plate subduction. The data include the Earth Gravitational Model (EGM2008), the General Bathymetric Chart of the Oceans (GEBCO) and gravity grids. The seismicity data were collected from the Incorporated Research Institutions for Seismology (IRIS) catalogue on 1970–2021. The variations in data were compared to analyse correlations between the geophysical, seismic and topographic parameters. Free-air gravity, geoid and topographic data derived from the high-resolution datasets were used to investigate their effects on the main seismic sources in the region. The comparison of the maps showed that the distribution of the shallow earthquakes in the Pacific segment of Panama coincides with negative free-air anomalies and lower geoid values. The results revealed high values of geoid in the high mountainous regions of Panama (Cordilliera de Talamanca, southern coast of Peninsula de Azuero and eastern Panama, 77.5–78.5°W), which correspond to the topographic roughness in the highlands. Negative values of geoid are found over the Caribbean Sea basin (−4 to 0 m). The analyses of seismicity showed 1740 earthquake events varying by magnitudes from 2.9 to 7.8 at the depths up to 225 m (near the west coast of Colombia). A high concentration of the earthquakes is in the western region of the Panama’s shelf waters (~82–83.5°W), and on the border with Colombia (~77–78.5°W). High gravity anomalies (over 220 mGal) are found in the mountainous regions which match the geodynamic processes associated with the Earth structure and geodetic and geophysical effects. The regions of the high seismicity were defined in the Gulf of Chiriqui and eastern part of the Gulf of Panama.

Geophysical investigation of the Mado Megamullion oceanic core complex: implications for the end of back-arc spreading

Detachment faulting is one of the main styles of seafloor spreading at slow to intermediate mid-ocean ridges. However, we have limited insight into its role in back-arc basin formation. We surveyed a remnant back-arc spreading center in the Philippine Sea and determined the detailed features and formation processes of the Mado Megamullion (Mado MM) oceanic core complex (OCC). This was undertaken in the context of back-arc evolution, based on the shipborne bathymetry, magnetics, and gravity with radiometric age dating of the rock samples collected. The Mado MM OCC has a typical OCC morphology with prominent corrugations on the domed surface and positive gravity anomalies, suggesting that there has been an exposure of the lower crust and mantle materials by a detachment fault. The downdip side of the detachment continues to the relict axial rift valley, which has indicated that the Mado MM OCC was formed at the end of the back-arc basin opening. The spreading rate of the basin decreased once when the spreading direction changed after six million years of stable trench perpendicular spreading. The rate then further decreased immediately prior to the end of the spreading when the Mado MM OCC was formed. The existence of other OCC-like structures in the neighboring segment and the previously reported OCCs along the Parece Vela Rift have indicated that the melt-poor, tectonic-dominant spreading is a widespread phenomenon at the terminal phase of back-arc spreading. The decrease in spreading rate in the later stage is consistent with the previous numerical modeling because of the decrease in trench retreat. In the Izu–Bonin–Mariana arc trench system, the rotation of the spreading axis and the resultant axis segmentation have enhanced the lithosphere cooling and constrained mantle upwelling, which caused the tectonic-dominant spreading at the final phase of the basin evolution.