Marquardt inverse modeling of gravity anomalies due to anticlinal and synclinal structures based on parabolic density contrast. (A case study: Kerend region)

In this paper, a method based on the 2D Marquardt inverse modeling of anticlinal and synclinal structures using the gravity field data is introduced and the density contrast of the difference depths of the earth is computed based on a parabolic density function (PDF). The normal and inverted isosceles triangular models are generally used to describe the geometries of these structures in analyzing gravity anomalies. In the absence of known geology, it may not be possible to isolate completely the gravity signature due to a geological structure from the regional gravity background. In this paper a computer program solves three different parameters of the structure, z1, z2 and i, in addition to estimating two coefficients of regional gravity anomaly. The modeling process begins with computing the theoretical gravity anomaly of an anticline or syncline prototype, defined by approximate shape parameters in each case that can be attained from known geology. The program reduces the error between the observed gravity anomaly and the estimated gravity anomaly by improving the initial parameters of the model during repetition until the misfit function falls below a predefined allowable error or the damping factor acquires a large value or the specified number of iterations is completed. The efficiency of the algorithm is illustrated with a set of synthetic gravity anomalies over an anticlinal and a synclinal structure both with and without regional background, further, the code is exemplified with the gravity data from Kerend region, Iran. The target of gravity survey studies is determination the limits and depth values of anticlinal structures as a probable hydrocarbon traps. The results show the top depth of the anticlinal about 2800 m, the bottom depth of the anticlinal about 4200 m and the bottom depth of the synclinal about 5600 m.