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1

L0-norm gravity inversion with new depth weighting function and bound constraints

Gebre Mesay Geletu, Lewi Elias

Acta Geophysica

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2022

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Vol. 70, no 4

1619--1634

EN

Delineating geologic features through the inversion of gravity data is an important goal in a range of geophysical investigations. However, it is a well-known fact that gravity data inversion has no inherent depth resolution. In order to overcome this limitation, different depth weighting approaches have been developed. With the purpose of finding an effective and a more convenient way to precisely estimate the depth of the anomalous body, we have tested the most popularly used depth weighting function. Our test showed that it does not properly counteract the decay of the gravity kernel and is strongly dependent on the exponent term. To resolve this, we have proposed a new depth weighting function that can easily be automated and counteracts the depth dependent natural decay of the gravity kernel more appropriately. Through this, the challenges in trial and error selection of the exponent of the old depth weighting function are avoided. The new depth weighing function was then implemented to improve a gravity inversion method, which produces compact and sharp images of the subsurface density distributions. The inversion method is obtained from the minimization of an objective function, which consists of data misfit and L0-norm stabilizing functions, by iteratively reweighted least-squares algorithm. To evaluate the practicality and resolution capability of the method, it was tested using a number of synthetic data sets from geometrically complex models and real data. The inversion results proved the effectiveness of our method in producing geologically acceptable multiple localized bodies with improved depth resolution. This in turn illustrates the applicability of the newly proposed function in the inversion of gravity data.

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Gravity inversion of basement relief using imperialist competitive algorithm with hybrid techniques

Joolaei Amir, Arab Amiri-Alireza, Nejati Ali

Acta Geophysica

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2022

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Vol. 70, no 6

2629--2646

EN

Classically, local deterministic optimization techniques have been employed to solve such nonlinear gravity inversion problem. Nevertheless, local search methods can also be easily implemented and demonstrate higher rates of convergence; but in highly nonlinear cases such as geophysical problems, they require a reliable initial model which should be adequately close to the true model. Recently, global optimization methods have shown promising results as an alternative to classical inversion methods. Each of the global optimization algorithms has unique benefits and faults; therefore, applying different combinations of them is one of the proposed solutions for overcoming their distinct limitations. In this research, the design and implementation of the hybrid method based on a combination of the imperialist competitive algorithm (ICA) and firefly algorithm (FA) as tools of two-dimensional nonlinear modeling of gravity data and as a substitute for the local optimization methods were investigated. Hybrid of ICA and FA algorithm (known as ICAFA) is a modified form of the ICA algorithm based on the firefly algorithm. This modification results in an increase in the exploratory capability of the algorithm and improvement of its convergence rate. This inversion technique was first successfully tested on a synthetic gravity anomaly originated from a simulated sedimentary basin model both with and without the presence of white Gaussian noise (WGN). At last, the method was applied to the Bouguer anomaly from a real gravity profile in Moghan sedimentary basin (Iran). The results of this modeling were compatible with previously published works which consisted of both seismic analysis and other gravity interpretations. In order to estimate the uncertainty of solutions, several inversion runs were also conducted independently and the results were in line with the final solution.

3

3D Gravity Inversion using Tikhonov Regularization

Toushmalani R., Saibi H.

Acta Geophysica

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2015

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Vol. 63, no. 4

1044--1065

EN

Subsalt exploration for oil and gas is attractive in regions where 3D seismic depth-migration to recover the geometry of a salt base is difficult. Additional information to reduce the ambiguity in seismic images would be beneficial. Gravity data often serve these purposes in the petroleum industry. In this paper, the authors present an algorithm for a gravity inversion based on Tikhonov regularization and an automatically regularized solution process. They examined the 3D Euler deconvolution to extract the best anomaly source depth as a priori information to invert the gravity data and provided a synthetic example. Finally, they applied the gravity inversion to recently obtained gravity data from the Bandar Charak (Hormozgan, Iran) to identify its subsurface density structure. Their model showed the 3D shape of salt dome in this region.