Abstract The spectra of gravity and magnetic anomalies due to a prismatic body can be expressed as sums of exponentials. The complex exponents of these exponentials are functions of frequency and locations of the corners of the body. An exponential approximation method is used for the analysis of the radial spectra of an anomaly and its first order moments for obtaining accurate estimates of the depths to the top and bottom of the body. A method has also been developed for determining approximately the location of the centroid of the body. When the location of the centroid and the depths to the top and bottom are known for the causative body, it is possible to calculate the horizontal dimensions with the help of the spectrum of the anomaly.

Abstract The analytic solution of the gravity anomaly caused by a 2D irregular mass body with the density contrast varying as a polynomial function in the horizontal and vertical directions is extrapolated from a historical version in which the analytic solution for the gravity anomaly was given only at the origin of the coordinate system to any point for the density function in terms of variables relative to that origin. To calculate the gravity anomaly at stations that are not at origins, a coordinate transformation is performed, in which case the polynomial density contrast function must also be expressed in the transformed coordinates, or a transformed solution must be obtained. These analytic solutions can be obtained at any station using (1) a solution transformation method, in which the density function and boundary of a mass body are kept intact, or (2) a coordinate transformation method, in which polynomial coefficient and boundary of a mass body are transformed accordingly. The issue of singularity and instability of the analytic methods has been related to case studies. Caution should be exercised in modeling or interpreting the gravity survey data using the analytic methods for large target-distance-to-target-size ratios outside the range of numerical stability. Compared with other published methods, the analytic solution results agree very well with other numerical or seminumerical methods, indicating the solution is correct and can be applied for any gravity anomaly calculation caused by an irregular 2D mass body with the density-contrast approximated as a polynomial function of horizontal position and/or vertical position when the observation is within the range of numerical stability.

The gravity maps display, in Bipindi zone, local oval culminations of low anomalies indicative of a presence of intrusive light body in a subsurface but the nature, the form and the position of this body are still unknown. The analyses of established gravimetric anomaly maps, the multi-scale evaluation of maxima of gradients and the quantitative interpretation of residual anomalies by 3D modelling permit characterizing the intrusive light body situated at Bipindi. The multi-scale evaluation of maxima of gradients shows that the modelling of the intrusive light body of Bipindi can be done without the problem of interference of anomalies from different sources. The 3D model of Bipindi zone shows two dissymmetrical blocks of the same type of rock with a density contrast of -0.095 g·cm-3 in comparison with the density of the surrounding metamorphic rocks. The two blocks are at a distance about 3 km from one to another. The upper surfaces of these blocks lie at a depth between 1 and 2 km. Their lower surfaces have two landings; one lies at a depth of about 8 km and another at a depth about 14 km. A consideration of the density of the modelled body, of the ranges of densities of specific rocks present in the general region indicates that the body may be composed of nepheline syenites. The intrusive body of Bipindi is situated in a senestral shear zone. The area situated between the two blocks of this intrusive body may be indicated for a detail study in the domain of mineral research.

The Complete Bouguer Anomaly (CBA) map from 1997 gravity survey at Karaha-Telaga Bodas, West Java, Indonesia is used to make a model of the subsurface geothermal system. A two-dimensional cross-section of the system is produced using a 2.5-D forward modeling. Initially, the print CBA maps of the Karaha-Telaga Bodas geothermal system is digitized. Next, the digital map is separated by using the moving average and spectral filtering methods, so a regional and residual anomaly maps are obtained. The subsurface modelling is made based on geological information of the area to produce a model that can represents the real condition as similar as possible. The line chosen for modelling has a North - South orientation, passing through Karaha and Telaga Bodas to foresee both of the geothermal system in one cross-section. Subsurface model interpretation shows that there are two separate granodiorite intrusion body with density contrast of 0.5 g/cc below Karaha - Telaga Bodas. This conclusion coincides with the intrusion body found during drilling operation. The intrusion body is possibly the heat source of the system. The reservoir of this system is interpreted as volcanic breccia with thickness of two kilometres in Telaga Bodas and keeps thinning towards Karaha. The fluids of the Karaha-Telaga Bodas Geothermal System are estimated to come from acid sulphate water and meteoric water entering from Telaga Bodas, as well as meteoric water entering from Karaha. There is an upflow in the South, Telaga Bodas.

Abstract We have studied the mathematical basis for the generation of gravity anomalies (Chapter 3), gravity instrumentation that enables gravity surveys and generally available surveying methods for obtaining them (Chapter 4), density variations and methods for determining rock density (Chapter 5), and the reduction of gravity data in static and dynamic settings (Chapter 6), which is intended to eliminate often very substantial measured effects that are unrelated to the gravitational sources we wish to analyze. Both relative-and absolute-gravity measurements are available in gravity exploration. Six generalized purposes of gravity surveys can incorporate one or both methods of measurement: 1)determination of the earth’s shape2)determination of missile trajectories, a military application now seldom used3)tidal and earth elasticity studies4)other time-dependent applications (such as the monitoring of reservoirs)5)determination of physical constants6)determination of the subsurface geology or other characteristics of the earth’s structure The last of these, the study of the subsurface, requires identification of the anomalies associated with the geologic sources of interest (anomaly separation) and an explanation of those anomalies in terms of the geology that is the purpose of the investigation. We will now turn to those activities. In this chapter, we examine the guidelines and limitations of anomaly interpretation. In Chapter 8, we examine inversion, a special case of inter

In urban areas with complex geological formations, such as Petaling Jaya in western Peninsular Malaysia, assessing subsurface conditions is crucial for the safe and efficient design of infrastructure foundations. Traditional methods often fail to address the variability and heterogeneity of soil-rock profiles, which are key to predicting load-bearing capacity and preventing structural failures. This study introduces a novel microgravity-geotechnical approach, integrating Bouguer and residual with enhanced gravity-derivative and gravity anomaly depth-structure modeling as well as borehole data (SPT-N and RQD) to examine subsurface features and structural instabilities. The gravity models highlight significant low-density anomalies corresponding to weathered silty sands, sandy silts, and fractured limestone, while derivative and tilt angle maps reveal curvilinear structures, suggesting tectonic or karstic dissolution processes. These features, along with observed weak zones, exacerbate the risk of uneven settlement, subsidence, and structural damage, which are already evident in the area's infrastructure. Borehole and depth-structure gravity models confirm variability in subsurface materials, with competent layers extending between 18 and 85 m in depth, underscoring the importance of precise foundation siting. Areas with low-density or fractured materials are evidently unsuitable for shallow foundations and require reinforcement, including deep foundation anchoring and specialized piling. The findings of this research provide critical insights for infrastructure design in regions with complex geological features, offering guidance on reliable siting and remediation of failing infrastructure. The approach established in this study can be applied to other terrains facing similar subsurface challenges, promoting safer and more resilient infrastructure development.