Residual Anomalies Research Articles

Aortic dilation in adults with repaired tetralogy of Fallot: a single-centre study.

Tetralogy of Fallot is the most prevalent cyanotic CHD. With the advent of advanced surgical methods, the majority of tetralogy of Fallot patients reach adulthood. However, many need re-intervention for the residual anomalies including residual right ventricular outflow obstruction, pulmonary regurgitation, residual ventricular septal defects, and progressive aortic dilatation. Aortic dilation could lead to aortic regurgitation or dissection requiring surgical correction. In the current study, we aimed to determine the prevalence and outcomes of aortic root dilatation in adults with repaired tetralogy of Fallot in our tertiary care centre. In this retrospective study, 730 consecutive patients with history of repaired tetralogy of Fallot were included. Aortic diameter at the level of annulus, the sinus of Valsalva, sinotubular junction, and the ascending aorta as measured by echocardiography were evaluated. Prevalence of outcomes necessitating re-intervention including aortic regurgitation and dissection were recorded. The mean size of annulus, sinus of Valsalva, sinotubular-junction, and ascending aorta in the latest available echocardiography of patients were 2.4+/-0.4 cm, 3.3+/-0.5 cm, 2.9+/-0.5cm, and 3.2+/-0.5cm, respectively. Prevalence of dilatation of sinus of Valsalva, dilation of Ascending aorta, sinotubular-junction, and aortic annulus was 28.7%, 21%, 8.3%, and 1 %, respectively. Five patients had severe aortic regurgitation (0.6%) and underwent surgical repair. One of these patients presented with acute aortic dissection. Aortic dilation is common in tetralogy of Fallot but prevalence of redo surgery for aortic dilation, regurgitation, and adverse events including acute dissection is low.

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.

Identifikasi Jenis Batuan Panas Bumi Di Desa Angseri Dan Sekitarnya Dengan Metode Gravitasi

The research has been done on 2D model of the subsurface structure of the hot springs in Angseri Village and its surroundings using the gravity method. The purposes of the research is to determine the distribution of gravity anomaly values, density values and subsurface rock structures. The results showed that the value of Bouguer anomaly was between 10-137 mGal, the regional anomaly was between 42-105 mGal, and the residual anomaly was between (-32)-(35) mGal. The modeling results showed that the subsurface structure of the study area was composed of lava rock (1.1-1.73 gr/cm3), tuff (1.61-2.52 gr/cm3), tuff breccia (2.51-2,79 gr/cm3), lava (2.8-2.89 gr/cm3) and volcanic breccia (2.9-3.2 gr/cm3), where volcanic breccia rocks as permeable rocks and tuff breccia rocks as cover rocks.

Penentuan Fasies Sentral Gunung Api Purba Menggunakan Metode Gravitasi Pada Kawasan Gunung Ijo, Pegunungan Kulonprogo

The Kulon Progo Mountains are a range of Old Volcanoes that are no longer active so that the body is difficult to identify as a volcano body. One of the old volcanoes in the Kulon Progo Mountains is Mount Ijo. The description of the subsurface through the characteristics of the existence of ancient volcanoes uses a geophysical method approach, namely the gravity method with supporting data in the form of geological studies of the Mount Ijo area. This is done to get the distribution of variations in the subsurface gravity field of Mount Ijo. The gravity data used is GGMPlus gravity satellite data with a lot area of 8.32 x 14.23 Km with a point distribution of 2368 points. In the processing process, a derivative analysis is carried out using Total Horizontal Derivative (THD) and Total Derivative (TDR). The results obtained from the ABL value of the Mount Ijo area illustrate the distribution of gravity anomaly values with high values ranging from 0.2 mGal to 3.5 mGal in the center of the map indicating the presence of the peak of Mount Ijo which is the central facies of Mount Ijo. Supported by the presence of structures in the form of faults and intrusion hills included in the proximal facies surrounding the central facies. The 2.5-dimensional model of the 2 incisions of the residual anomaly map has a depth of 800m and produced a picture of the central facies, proximal facies and a small part of the medial facies of Mount Ijo.

Geothermal potential analysis using 3d modeling of subsurface structures based on the Gravity Anomaly in the Mount Lawu area, Central Java

Over time, energy needs will continue to increase. Dependence on the use of fossil energy results in the availability of such energy will run out at any time, so it is necessary to develop research on geothermal energy that is environmentally friendly and renewable. One of the Geothermal Work areas is on Mount Lawu, located at coordinates between 111°15' east longitude and 7°30' south latitude in several districts Central Java Province and East Java Province. The purpose of this study is to provide information related to geothermal potential using the gravity method by knowing the temperature of the area and the 3D modeling of subsurface structures. Based on the results of the Second Vertical Derivative (SVD) analysis, three normal faults were found in geothermal sources. The modeling results show that the residual anomaly map depicts a distribution of high anomalies ranging between 2 mGal up to 6.5 mGal scattered from North to South and East to West, suspected to be caused by lava rock intrusion. The results of the 3D inversion model show there are three layers, namely clay rock, which is suspected to be cap rock at a depth of 500 - 2500 m, pyroclastic lava rock, which is suspected to be as a reservoir at a depth of 3000 - 4500 m, and lava, which is suspected to be as a reservoir heat source at a depth of 5000 - 8000 m. Based on the map in Land Surface Temperature (LST) obtained the temperature value of Mount Lawu ranging from 3.14 °C - to 23.25 °C.

Delineation of geological structures of Arta geothermal prospect in Djibouti based on the gravity data analysis and interpretation

The Arta geothermal prospect is located in the southern part of the Gulf of Tadjoura, 45 km west of Djibouti city. This study uses 398 gravity data stations collected by the Djiboutian Office for Geothermal Energy Development (ODDEG) from February to May 2018. The geothermal activity of the Arta area is revealed by surface thermal manifestations, such as near-boiling fumaroles (98 °C). This study aims to delineate the subsurface geological structures responsible for surface geothermal manifestations and define the depth and geometry of the geothermal reservoir in the study area. A Complete Bouguer anomaly was obtained using a Bouguer density of 2.55 g/cm3, derived as an average density from the F-H, G-H and CVUR methods. A regional and residual anomaly trend separation method was applied to focus on the structures of interest in the study area, and a residual Bouguer anomaly map was obtained. Edge detection filters, including Horizontal Derivatives (HD) and an Improved Normalized Horizontal tilt angle (INH), were used to examine the gravity data for edge identification. The density was then modelled in three-dimensional (3-D), utilizing the VOXI Earth Modeling Tool performed in Geosoft Oasis Montaj. The model was constrained using estimated lower (-0.35 g/cm3) and upper (0.65 g/cm3) bound density values from the expected density values of the local geology. The Bouguer and residual anomaly maps show a high-density body in the central part, surrounded by low-anomaly structures. The high-density body is interpreted as an intrusive body covering the basement of the study area. The anomalies imaged from HD and INH indicate a significant number of high gradient anomalies trending N-S, NE-SW, and NW-SE, corresponding to the trend of the geological structures of the Arta geothermal prospect. These high-gradient anomalies can be interpreted as faults, contact zones, or geological boundaries. The 3-D model imaged a high-density anomaly trending N-S in the central part at 2 and 3 km below sea level with a volume of about 126 km3 and an average block density of 2.66 g/cm3, interpreted as magma intrusion or intrusive volcanic rocks. The 3-D vertical cross-sections revealed that the intrusion is visible at depth and that some intrusions could be seen at the surface and near surface. The findings of this gravity study will contribute to the overall and future geothermal exploration and development of the Arta geothermal prospect.

Derivation of geomagnetic field to determine geothermal flow at Terak, Bangka Belitung

The Geothermal system on Bangka Belitung islands are characterised to a radiogenic type of non-volcanic geothermal energy. The presence of geothermal energy in this region can be attributed to the geological characteristics of granite rocks, which undergo processes such as fracturing, folding, or faulting. The primary objective of this study is to figure out the subsurface heat flow patterns within the geothermal region of Terak. The process of collecting data was conducted via a Proton Precession Magnetometer (PPM) instrument, which consisted of a track of 2.5 kilometres in length. The determination of subsurface heat flow patterns in total magnetic anomaly, regional anomaly, and residual anomaly was achieved through the application of the First Horizontal Derivative (FHD) and Second Vertical Derivative (SVD) algorithms. The findings indicate the presence of a subsurface heat flow pattern in the eastern region, which spreads towards the southeast and further extends to the southwest. Notably, this pattern is characterised by abnormal depths ranging from about 20 to 130 metres beneath the surface. The observed phenomenon was in line with the consistent occurrence of geothermal manifestations in the region.

Identification of Geothermal System in Cisolok, West Java based on the Correlation of Gravity Method, ADMT (Active Directory Magnetotelluric), and Drill Log Data

Indonesia has 40% geothermal potential of the world’s geothermal potential. One proof of its potential is in Cisolok, West Java. The method used in this study is the gravity method from 2013 GGMPlus satellite with First Horizontal Derivative (FHD) analysis which is correlated with ADMT and drill log data. Based on overlaid between Land Surface Temperature (LST) map and residual anomaly map, Cisolok has a temperature of around 23.8 – 26.5 °C. These correlations describe the normal fault structure in the south that controls the Cisolok geothermal system. The results of the 3D inversion modeling show alternating layers of tuff, tuff breccia and silt as a cap rock with a density contrast of 0 – 0.2 gr/cc at a depth of 0 – 325 m, thick limestone layers with a density contrast of -0.1 – (-0.05) gr/cc at a depth of 325 – 700 m, and a layer of granodiorite rock as an intrusion body with a density contrast of -0.2 – (-0.15) gr/cc at a depth of 700 – 900 m. Based on the results obtained, it can be proven that the gravity method and the ADMT method have a fairly good correlation in geothermal exploration activities.

Overdeepenings in the Swiss plateau: U-shaped geometries underlain by inner gorges

We investigated the mechanisms leading to the formation of tunnel valleys in the Swiss foreland near Bern. We proceeded through producing 3D maps of the bedrock topography based on drillhole information and a new gravimetric survey combined with modelling. In this context, the combination of information about the densities of the sedimentary fill and of the bedrock, together with published borehole data and the results of gravity surveys along 11 profiles across the valleys, served as input for the application of our 3D gravity modelling software referred to as PRISMA. This ultimately allowed us to model the gravity effect of the Quaternary fill of the overdeepenings and to produce cross-sectional geometries of these troughs. The results show that 2–3 km upstream of the city of Bern, the overdeepenings are approximately 3 km wide. They are characterized by steep to oversteepened lateral flanks and a wide flat base, which we consider as a U-shaped cross-sectional geometry. There, the maximum residual gravity anomaly ranges between − 3 to − 4 mGal for the Aare valley, which is the main overdeepening of the region. Modelling shows that this corresponds to a depression, which reaches a depth of c. 300 m a.s.l. Farther downstream approaching Bern, the erosional trough narrows by c. 1 km, and the base gets shallower by c. 100 m as revealed by drillings. This is supported by the results of our gravity surveys, which disclose a lower maximum gravity effect of c. − 0.8 to − 1.3 mGal. Interestingly, in the Bern city area, these shallow troughs with maximum gravity anomalies ranging from − 1.4 to − 1.8 mGal are underlain by one or multiple inner gorges, which are at least 100 m deep (based on drilling information) and only a few tens of meters wide (disclosed by gravity modelling). At the downstream end of the Bern area, we observe that the trough widens from 2 km at the northern border of Bern to c. 4 km approximately 2 km farther downstream, while the bottom still reaches c. 300 to 200 m a.s.l. Our gravity survey implies that this change is associated with an increase in the maximum residual anomaly, reaching values of − 2.5 mGal. Interestingly, the overdeepening’s cross-sectional geometry in this area has steeply dipping flanks converging to a narrow base, which we consider as V-shaped. We attribute this shape to erosion by water either underneath or at the snout of a glacier, forming a gorge. This narrow bedrock depression was subsequently widened by glacial carving. In this context, strong glacial erosion upstream of the Bern area appears to have overprinted these traces. In contrast, beneath the city of Bern and farther downstream these V-shaped features have been preserved. Available chronological data suggest that the formation of this gorge occurred prior to MIS 8 and possibly during the aftermath of one of the largest glaciations when large fluxes of meltwater resulted in the fluvial carving into the bedrock.

Multi-Elevations Upward Continuation Method to Depth Detection of the Main Crustal Layers in Western Desert of Iraq

The upward continuation technique was applied to the gravity and RTP magnetic data to obtain the residual anomalies maps in the western part of Iraq. Twelve upward elevation residual gravity maps and another twelve upward elevation residual RTP magnetic were determined using the same twelve upward continuation elevations. The applied upward elevations range from 1000 to 55000 m. The total range of the residual anomalies maps (Color Bar range) of gravity and RTP magnetic were plotted against the upward elevations. Five segments and four intersection points were obtained for the gravity and magnetic data. The trace of these intersection points on the upward elevation axis approximately indicate the following values 4.4-5, 12.8-13.5, 27-24, and 39-39.6 km. These values may indicate the depth of the following layer boundaries, the Burj Formation ( Mid-Cambrian), basement, mid layer in the basement rocks, and the Moho depth. The authors believe it is possible to apply the upward continuation to find the main layers which show abrupt change in the physical properties

Internal structure of the southern and central Colima Volcanic Complex, western Mexico, revealed by 3D modeling of aeromagnetic data

We present the results of an aeromagnetic survey performed over the central Colima Volcanic Complex situated in the western region of Mexico. Within the interpolated residual anomaly map, four prominent anomalies appear in sight. Notably, three of these anomalies are closely linked to the major volcanoes in the area: Colima (also recognized as Fuego), Nevado, and Cántaro. Moreover, the data indicate the existence of magnetic anomalies of different amplitudes and wavelengths apparently associated with intrusive bodies. The Colima and Nevado volcanoes are characterized by large amplitude dipolar anomalies. The inversion procedure reveals 3D causative bodies that can be recognized as shallower remnants of their magmatic reservoirs. They seem to be connected to larger and deeper bodies. The inversion procedure delineates four distinct source bodies. The deeper body among these primary structures displays a volumetric extent approximating 13.6 km³, positioned at depths spanning from 4.7 to 6.0 km below the summit. Another noticeable body, associated with the Colima volcano, has a semi-triangular shape with a volume of some 8.2 km3, located between 2.6 and 3.1 km. The third body, associated with Nevado, exhibits a vertically elongated shape located from depths of the order of 1.8–2.2 km. Towards the northeastern vicinity of Nevado, a fourth distinctive body becomes evident. This body also presents an elongated form, somewhat inclined in orientation, and occupies a depth interval of 2.2–2.6 km.

Occurrence Characteristics of Lead–Zinc Mine and Low-Flying Aeromagnetic Prospecting in a Forested Region of Yichun City

Understanding the characteristics of lead–zinc mine occurrences and mastering effective investigative techniques are paramount in modern ore prospecting. This research focuses on the forested region of Yichun city in China, with a specific emphasis on the strategic mineral resource of a lead–zinc mine. The study examines the distribution patterns of this mineral and employs advanced aeromagnetic exploration methods. Firstly, we analyzed the geological structure and features of the region by leveraging the latest high-precision aeromagnetic data collected using dynamic delta wing technology. This analysis was complemented by an assessment of the geological conditions of the research area, existing lead–zinc deposits, ground magnetic surveys, and verification studies. With the goal of establishing a meaningful correlation between aeromagnetic anomalies and lead–zinc deposits, we employed various potential field conversion techniques, including the reduction to the pole, vertical derivatives, upward continuation, and residual anomaly analysis techniques. Secondly, we investigated the metallogenic sites within this region and provided a comprehensive summary of the metallogenic circumstances and characteristics related to aeromagnetic prospecting. Thirdly, we employed human–computer interaction fitting inversion techniques to predict the potential for lead–zinc mine prospecting in areas exhibiting aeromagnetic anomalies. The study underscores the significance of high-amplitude and large-scale aeromagnetic anomalies in the study area. Furthermore, we examined the interplay between intrusive rocks, strata, and structural elements within the region to identify favorable conditions for lead–zinc mineralization. As a result of our analysis and discussions, a location was predicted where a lead–zinc mine may exist. The research methodology outlined in this article provides valuable insights for future lead–zinc mine exploration efforts in areas characterized by similar geological conditions.

Magnetic anomaly interpretation for a 2D fault-like geologic structures utilizing the global particle swarm method

We establish a method to interpret the magnetic anomaly due to 2D fault structures, with an evaluation of first moving average residual anomalies utilizing filters of increasing window lengths. After that, the buried fault parameters are estimated using the global particle swarm method. The goodness of fit among the observed and the calculated models is expressed as the root mean squared (RMS) error. The importance of studying and delineating the fault parameters, which include the amplitude factor, the depth to the upper edge, the depth to the lower edge, the fault dip angle, and the position of the origin of the fault, is: (i) solving many problem-related engineering and environmental applications, (ii) describing the accompanying mineralized zones with faults, (iii) describing geological deformation events, (iv) monitoring the subsurface shear zones, (v) defining the environmental effects of the faults before organizing any investments, and (vi) imaging subsurface faults for different scientific studies.Finally, we show the method applied to two theoretical models including the influence of the regional background and the multi-fault effect and to real field examples from Australia and Turkey. Available geologic and geophysical information corroborates our interpretations.

Comparison between Upward Continuation and Gaussian Techniques, and their Relation to the Source Depth, Case Study in Eastern Central Iraq

The IGMAS+ forward program is used to compare upward continuation and Gaussian wavelength techniques in separating residual from regional anomalies of gravity data of a synthetic model and case study area, in eastern central Iraq. The comparison indicate a certain relation between the upward continuation and the Gaussian wavelength cutoff, so it is possible to produce the same regional and residual anomaly maps using each one of them. For the study area, the Gaussian cutoff 115000 maps coincide with the upward 12km regional and residuals maps, also the Gaussian cutoff 455000 maps coincide the upward 54km.The relation between the parameters of the two techniques, in case of produce coincide maps, it may be used to obtain the depth of gravity anomaly causative sources. It is found that ratio of Gaussian wavelength cutoff parameter to the upward parameter multiplied by 1.25 equal to the average level depth below the deeper source causing the residual anomalies. The average depth of residual anomalies in the case study area found equal to 10.5 km. The basement depth in the study area were coincide with the depth values from previous studies and geologically is very acceptabile.

Analysis of Formation Ronggojalu Spring and Probolinggo Active Fault Continuity with Satellite Data Gravity Method

The Ronggojalu spring, with a discharge intensity of more than 3,000L/second, makes it one of the spring with the most significant discharge in Indonesia and is the main supplier of clean water for the City of Probolinggo. From the observation of topographic maps, the existence of this spring forms a lineament with Paras Spring and Sumber Kramat with a direction of Northeast to Southwest. The presence of this lineament can indicate the existence of geological structures that play a role in the formation of spring. In addition, this lineament is in the same direction as the active Probolinggo fault identified by PUSGEN (Pusat Studi Gempa Nasional). This study aims to identify the presence of geological structures in the lineament using satellite gravity data GGMplus (Global Gravity Model) and Remote Sensing. This data is quite efficient and effective in identifying subsurface geological structures. With the SVD (Second Vertical Derivative) analysis, the residual anomaly results from the second derivative value of the Bouger anomaly so that it can show the density contrast value as an indication of the geological structure. From the results of the interpolation of satellite gravity data in the study area, the CBA (Complete Bouguer Anomaly) value range is -16.8 – 4.8 mGal. The analysis of SVD and FHD shows a significant contrast different values along the fault line that passes through the spring. The lineament density processing also shows a weak zone around the fault zone, indicating the continuity in that zone. The existence of a fault under this spring indicates the influence of the fault on the formation of Ronggojalu Spring, Paras Spring, and Keramat Spring. In addition, it is estimated that this fault is a continuation of the active Probolinggo fault.

CONTRIBUTION OF AEROGRAVITY DATA INTERPRETATION TO THE STUDY OF THE DEEP STRUCTURE OF AGADEM PETROLEUM BLOCK (NIGER)

The main information provided by gravity maps is the geographical distribution of density heterogeneities in the subsurface. It is an important tool widely used for the mapping of geological structures, especially in the oil industry. Thus, this study based on the interpretation of aerogravity data has for objective, the qualitative description of the characteristics of the gravity anomalies of the study area, interpretation and mapping of the gravity lineaments as well as their depths, knowing that the lineaments constitute potential structural traps favorable to the accumulation of the hydrocarbons. Methods such as horizontal derivative, upward continuation and Euler deconvolution are used to give a geological signifiance to the different anomalies and to highlight deep structures. Thus, the analysis of the residual anomaly map revealed elongated negative and positive anomaly zones, oriented globally NW-SE, considered respectively as horst and graben zones. Gravity lineaments, considered as normal faults, are mapped using the horizontal gradient method. Finally, the depths of the density contrasts are estimated by the Euler deconvolution calculation using the value “1” as structural index. The depths thus determined are highly variable. The shallowest depths vary between 3000 m and 6000 m, while the deepest depths reach 18000 m.

Crustal structure across the Central part of Narmada-Son Lineament, India based on the interpretation of aeromagnetic and gravity data: Geological implications

Narmada-Son Lineament (NSL) is a prominent geo-tectonic feature located in central India, characterised by complex geological structures and evolution history. In this study, we present a detailed joint interpretation of the aeromagnetic and gravity anomaly maps to delineate the crustal structure in order to address the thermo-tectonic activity below the NSL region. The NW-SE linear trend observed in the aeromagnetic anomaly map correlates well with the major tectonic elements of the NSL and the Vindhyan basin. The low-pass filtered regional gravity anomaly map and corresponding residual anomaly map revealed several crustal-scale structural features in the study area. The Curie depth map of the region prepared from the magnetic anomaly map shows the variation between 24-48 km. The corresponding heat flow map correlates well with the trends in surface heat flow data. The gravity-derived Moho depth map reveals that the values vary between 30-40 km in the NSL region with deeper Moho below the Vindhyan basin. Further, the crustal models obtained from the constrained potential field modelling for two long transects across the NSL in the present study area revealed i) the absence of crustal underplating in the eastern part of NSL below Hirapur-Mandla region, ii) the presence of mid-crustal horst like structure below NSL in both the transects, iii) undulating Moho with higher density crustal rocks within the NSL compared to the surrounding areas. The modelled crustal structure and the analysis of Curie depth as well as heat flow maps of the study area, reveal that the NSL region was affected by repeated tectonic activities since the Proterozoic times, and the present-day tectonics of this belt is greatly influenced by the reactivation of pre-existing faults along the NSL.

3D Visualization of Geothermal System Structure Based on Inversion Model of Gravity Data. Case Study: Mt. Salak Region, West Java

The geothermal power plant located in Gunung Salak plays a crucial role in increasing the electricity supply transmitted to the Java-Bali region, as the energy demand continues to rise. The objective of this research is to determine the 3D subsurface structure of Gunung Salak, specifically the distribution of the reservoir as the target for geothermal energy using the Gravity method. Gravity data, including gravity disturbance (gd), geoid, and Digital Elevation Model (DEM), were obtained from the ICGEM website with a total of 48740 data each. Based on the results of the residual anomaly map, the low anomalies beneath Gunung Salak have values from -5.15 to -1.88 mGal, which are suspected to be associated with the magma chamber. The high anomalies beneath the manifestations have values from 0.92 to 5.01 mGal, indicating andesitic basalt intrusive rocks believed to be the reservoir rock. Through the 3D inversion modeling of the subsurface structure of the Gunung Salak geothermal system, a clay cap with a density from 2.47 to 2.5 g/cc at depths of 0 to 700 m and andesitic basalt rock as the reservoir with a density from 2.74 to 2.91 g/cc at depths of 700 to 3000 m have been identified.

Semarang Subsurface Model Using Airborne Gravity Data

The city of Semarang faults became active again in the Quaternary era. The gravity method has been widely used to identify subsurface conditions in Semarang City and its surroundings, especially the satellite gravity method and land gravity methods. Meanwhile, Semarang City and its surroundings have never used the airborne gravity method. Therefore, this study aims to identify subsurface conditions, especially faults, using airborne gravity data in Semarang and its surroundings. The airborne gravity value is the gravity value at a certain height. Therefore, in this study, the downward continuation process using Molodensky methods on airborne gravity data is useful for obtaining gravity values at topographical heights. Based on the residual anomaly map, there is a low gravity anomaly with a value range of -6.6 – (-0.5) mGal, located between high gravity anomalies, which have a value range of 1.7-7.4 mGal, which is suspected to be associated with a shallow structure in the form of a fault in the research area. Based on the residual anomaly map, the subsurface 2D model uses a forward model in areas identified as faults on the geological map. The model results have an error value of 0.221, representing a fit model that shows a picture of subsurface conditions close to the actual situation with fault structures on the D-D' Line. Keywords: Airborne gravity, fault, downward continuation, Molodensky method

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.