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The inversion of gravity data is one of the most important topics in the quantitative interpretation of practical data, since construction of density contrast models could increase the amount of information that can be achieved from the gravity data. This study shows the gravity response to the assumed model. In this model, where tthe sub-surface ground has been partitioned into 15×10 prisms ands the dimension of each prism is 20 m × 5 m. As is shown, the 2D model includes 9 prisms whose density contrast is 1000 kg/cm3. The inverted gravity correspondings to the resulted causative body from inverting the observed gravity. This inverted model that is corresponding to the exactly similar of to the original causative body, achieved at 4th iteration, where the L2 norm as the stopping criterion attained the smallest amount. We have used the reweighting focusing inversion method for inverting the gravity horizontal gradient data. The computed density distributions are located on the vertical borders of the sub-surface mass. The gravity horizontal gradient related to the assumed model. The inversion response to the gravity horizontal gradient related to the assumed model is demonstrated, asshows the estimated densitiesy are situated on the vertical edges of the model. The L2 norm of the as shows gravity horizontal gradient is 0.0036 mGal/m. We have applied the reweighting focusing inversion algorithm to invert the 2D gravity and its horizontal gradient data related to a salt dome situated in the Aji Chay, East Azerbaijan Province, Iran.from Iran. The calculated gravity horizontal gradient has been shown, where the L2 norm is 0.0833 mGal. The real gravity is related to a salt dome, situated in the Aji Chay, East AzerbaijanProvince, Iran. Salt domes in this region in terms of potash reserves are significant in terms of potash reserves. The inverted density contrasts for the sub-surface salt dome. We have applied the reweighting focusing inversion algorithm to invert the 2D gravity and its horizontal gradient data related to a salt dome from Iran. The method has been tested for a theoretical gravity set data, with and without added random noise random. The results demonstrate the ability of the reweighting focusing inversion method in recovering subsurface density contrast distribution and detecting the vertical border. [ABSTRACT FROM AUTHOR]

The flexural strength and consequently the elastic thickness (Te) of the lithosphere are often calculated utilizing the statistical relationships between gravity anomalies and topography data. The elastic thickness of the lithosphere is one of the most important parameters in determining the geological properties and characteristics of the crust as well as its rheological behavior. This prospective study was designed to investigate the use of the gravity and topography data in order to calculate the two fundamental functions, i.e. admittance and coherence, which are the basic functions for determining the elastic thickness of the lithosphere. In this research, the theory of the two objective functions is modeled. The study offers some important insights into the involved parameter and how they affected the functions. Additionally, the results show the impact of initial assumptions of different parameters on the retrieved value of the Te parameter. Taking into account the initial assumptions about parameters such as the elastic thickness (𝑇𝑒) of the plate, the loading ratio (𝑓) and the degree of correlation (𝑟) between the surface and subsurface loading regimes applied to the plate and using spectral methods, the value of these two functions are calculated. After examining the theoretical models, the real-data analysis is conducted in order to examine the observed values and compare them with the theoretical values. Based on what was mentioned in the following, this function can be able to retrieve the elastic thickness of the lithosphere. We concluded that: One of the more significant findings to emerge from this study, by examining the theoretical models, is that the best function to determine the elastic thickness of the lithosphere is to use the Bouguer coherence function. A comparison of the results reveals that the characteristic curves of the admittance function will change drastically with the change of the involved parameters. Consequently, having complete knowledge of the structure of the region and involved parameters is essential while using free air admittance in order to determining Te. As it was illustrated in this research, the characteristic curve of the coherence function can be used to determine Te based on the roll over wavelength. For the reason that there was no significant change in the shape of characteristic curve of the functions with the initial value of the loading ratio (𝑓), this parameter had less impact no the inversion process. Having considered rare correlation between free air gravity and topography, it is reasonable to accept that the free air coherence method is less applicable in determining Te than Bouguer coherence. The findings from previous studies provide support for the key arguments. [ABSTRACT FROM AUTHOR]

In water resources management, correct identification of bedrock characteristics, such as type, depth and structure is useful and various geophysical methods are used for this purpose. In geophysical and subsurface investigations, solving inverse problems using physics of the problem in partial differential equation (PDE) system is very important. Inverse modeling is one of the useful solutions which creates a logical model between observed and measured values. The limitations and ambiguity of individual techniques can be significantly reduced by adopting joint inversion schemes. Using inversion approaches which combine two or more geophysical methods, allows substantial improvements in modeling processes. The joint inversion of different electromagnetic and resistivity data sets in hydrogeology, structural geology and mining has been used in some studies but the gravity method is less used in hydrogeological investigations. One example of using gravity method in previous studies is an algorithm for joint inversion of gravity and resistivity data, where the interfaces corresponding to changes in the bulk density were interpreted as interfaces of porosity and water content changes, i.e. interfaces of electrical resistivity changes. In this paper, we present a framework for joint inversion of gravity and geoelectric data solving under-determined inverse problems. It can be used in a wide range of physical systems governed by PDEs. The integrated approach is based on the connection between density and resistivity of a sedimentary sequence through the porosity. Also, we present a general adjoint state formulation which may be used in this framework. It increases the calculation speed of sensitivity matrices in a variety of commonly encountered under-determined problems. There are two steps in this research. First, 2D joint inversion of gravity and geoelectric data is run and validated in COMSOL multi-physics software using one synthetic model and synthetic data in a forward modeling process. Afterwards, using real gravity and geoelectric data surveyed along a cross-section in part of the Qotrum plain in the SE Yazd, the lateral structure of bedrock is estimated. Because Qotrum basin is already well surveyed, it offers opportunities for evaluation of accuracy and reliability in joint inversion approaches. Fifty-one gravity stations and eleven vertical electrical soundings were carried out across the central part of this basin to apply the proposed joint inversion. The results indicated that gravity-geoelectric joint inversion is more accurate than the individual interpretation of each of these methods and significantly improves the solution by decreasing the ambiguity of models. Furthermore, this method, while high in computational speed, can be used in modeling of a wide range of geophysical, hydrogeological and physical systems governed by the partial differential equation laws. [ABSTRACT FROM AUTHOR]

In this study, Simulated Annealing algorithm is applied on Rayleigh wave group velocities to image the density variations and shear and compressional wave velocities structure of the crust and upper-mantle of Makran subduction zone. Based on previous studies, surface wave dispersion measurements are primarily sensitive to seismic shear wave velocities. However, it has been proved that the sensitivity to compressional wave velocity is significantly smaller than the sensitivity to shear wave velocity. Also the sensitivity function for the density is smaller than the one for the shear wave velocity. Therefore, shear wave velocity variations are mainly the model parameters in surface wave dispersion analysis. Simulated Annealing is a probabilistic technique for finding the global optimum of a given function. It is especially useful to approximate global optimization in a large search space. The Simulated Annealing method like the Monte-Carlo method, samples the whole model space and can avoid getting stuck in local minima. To evaluate calculation efficiency and effectiveness of Simulated Annealing algorithm, two noise-free and two noisy (10% of white Gaussian noise) synthetic data sets are firstly inverted. Then, a real data from Makran region is inverted to examine the applicability and robustness of the proposed approach on real surface wave data. In next step, gravity data inversion was applied with a priori information based on surface wave analysis results to obtain Moho depth variations and crustal density structure. The reason for using gravity data set is that surface waves group velocity is sensitive to average velocity variations and has a good lateral sensitivity, whereas gravity anomaly is sensitive to depth variations of discontinuities and has a good vertical resolution. Our results show that the Moho depth across the Makran subduction zone increases from the Oman seafloor and Makran forearc setting to the volcanic arc. Generally, the crust in the western Makran is thicker than the eastern part and the maximum crustal thickness in the Makran region reaches 46 to 48 km below the Taftan-Bazman volcanos. The Moho map clearly depicts the western edge of the Makran subduction zone, where the Minab fault (representing the eastern edge of the Hormuz Straits) marks the boundary between the thick continental crust of the Arabian plate and the thin oceanic crust of the Oman Sea. Our results show clearly that the high-velocity slab of the Arabian plate subducts northwards beneath the low-velocity overriding lithosphere of Lut block in the western Makran and Helmand block in the eastern Makran. [ABSTRACT FROM AUTHOR]