Document Type : Original Research Paper


1 Geophysic Institute,University of Tehran, Tehran, Iran

2 Geological Survey of Iran, Tehran, Iran

3 Geophysic Institute,University of Tehran, Tehran, Iran Geological Survey of Iran, Tehran, Iran

4 Geophysic Institute,University of Tehran, Tehran, Iran Management of Oil Exploration, Tehran, Iran


Determination of the geometry of bedrock, by nonlinear inverse modeling of gravity data, is the aim of this paper. In this method, reliable geological structures can be obtained by minimum geology priori information. The usual practice of inverting gravity anomalies of two-dimensional bodies replaced by n-sides polygon for determining location of the vertical that best explain the observed anomalies. In this method, the geometry of the bedrock is replaced by a series of juxtaposing prisms. Finally the length of each prism is the depth of the bedrock at that point.
The algorithm uses a nonlinear iterative procedure for simulation of bedrock geometry. At the first step, the nonlinear problem changes to a linear problem by a proper approximation and standard method. The second step is the parameterization of the model. Finally, an initial model is suggested on the basis of geological and geophysical assumption and using the numerical analysis, Jacobean matrix is calculated. In each iteration the inversion will improve the initial model, considering the differences between observed and calculated gravity anomalies, based on Levenberg-Marquardt's method.
The practical effectiveness of this method is demonstrated by inversion of synthetic (free noise and noise contaminated data) and real examples. The real data is acquired over the Moghan area and the results compared with the geological information.


Bhattacharya, B. K. &  Navolio, M. E., 1975- Digital convolution for computing gravity and magnetic anomalies due to arbitrary bodies. Geophysics 40 (6), 981–992.    
Bott, M. H. P., 1960- The use of rapid digital computing methods for direct gravity interpretation of sedimentary basins. Geophysical Journal of the Royal Astronomical Society 3, 63–67.
Marquardt, D. W., 1963- An algorithm for least-squares estimation of non-linear parameters: Jour. Sac. Indust. Appl. Math., v. II no. 2, p. 431-441.
Morgan, N. A. & Grant, F. S., 1963- High speed calculation of gravity and magnetic profiles across two-dimensional bodies  havingan arbitrary cross-section. Geophysical Prospecting 11 (1), 10–15.
Murthy, I. V. R. &  Rao, S. J., 1989- A Fortran 77 program for inverting gravity anomalies of two-dimensional basement structures. Computers & Geosciences 15 (7), 1149–1156.
Radhakrishna Murthy, I. V. & Rama Rao, P., 1993- Inversion of gravity and magnetic anomalies of two-dimensional polygonal cross-sections. Computers & Geosciences 19 (9), 1213–1228.
Rao, B. S. R. & Murthy. I. V. R., 1978- Gravity and magnetic methods of prospecting: Arnold-Heinemann (India) Pvt. Ltd., AB,9 Safdar jang Enclave. New Delhi,390 p.
Roy, A., 1962- Ambiguity in geophysical interpretations. Geophysics 27 (1), 90–99                
Talwani, M., Worzel, J. &  Ladisman, M., 1959- Rapid gravity computations for two dimensional bodies with application  to the Mendocino submarine fracture zone. Journal of Geophysical Research 64 (1), 49–59.